WO2009103124A1 - Semiconductor device including nanocrystals and methods of manufacturing the same - Google Patents
Semiconductor device including nanocrystals and methods of manufacturing the same Download PDFInfo
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- WO2009103124A1 WO2009103124A1 PCT/AU2009/000197 AU2009000197W WO2009103124A1 WO 2009103124 A1 WO2009103124 A1 WO 2009103124A1 AU 2009000197 W AU2009000197 W AU 2009000197W WO 2009103124 A1 WO2009103124 A1 WO 2009103124A1
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- WIPO (PCT)
- Prior art keywords
- inorganic
- etl
- htl
- layer
- wet
- Prior art date
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- 238000000034 method Methods 0.000 title claims abstract description 69
- 239000002159 nanocrystal Substances 0.000 title claims abstract description 69
- 239000004065 semiconductor Substances 0.000 title claims abstract description 60
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 28
- 239000004054 semiconductor nanocrystal Substances 0.000 claims description 60
- 239000002243 precursor Substances 0.000 claims description 55
- 238000005234 chemical deposition Methods 0.000 claims description 50
- 238000000151 deposition Methods 0.000 claims description 30
- 238000010438 heat treatment Methods 0.000 claims description 23
- 230000005525 hole transport Effects 0.000 claims description 20
- 229910052751 metal Inorganic materials 0.000 claims description 19
- 239000002184 metal Substances 0.000 claims description 19
- 239000000758 substrate Substances 0.000 claims description 17
- 239000006193 liquid solution Substances 0.000 claims description 14
- 150000003839 salts Chemical class 0.000 claims description 14
- 230000008021 deposition Effects 0.000 claims description 13
- 238000004528 spin coating Methods 0.000 claims description 13
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- 238000009833 condensation Methods 0.000 claims description 2
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- 239000002096 quantum dot Substances 0.000 abstract description 16
- 238000012545 processing Methods 0.000 abstract description 5
- -1 for instance Substances 0.000 abstract description 3
- 239000010410 layer Substances 0.000 description 133
- 239000000243 solution Substances 0.000 description 41
- 239000000463 material Substances 0.000 description 24
- 239000002245 particle Substances 0.000 description 24
- XLOMVQKBTHCTTD-UHFFFAOYSA-N zinc oxide Inorganic materials [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 21
- 239000011787 zinc oxide Substances 0.000 description 21
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 14
- 239000010408 film Substances 0.000 description 14
- 239000000126 substance Substances 0.000 description 14
- 239000010409 thin film Substances 0.000 description 14
- UHYPYGJEEGLRJD-UHFFFAOYSA-N cadmium(2+);selenium(2-) Chemical compound [Se-2].[Cd+2] UHYPYGJEEGLRJD-UHFFFAOYSA-N 0.000 description 13
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 12
- 239000002904 solvent Substances 0.000 description 11
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 9
- 239000011159 matrix material Substances 0.000 description 8
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 8
- 239000012703 sol-gel precursor Substances 0.000 description 8
- 238000000137 annealing Methods 0.000 description 7
- 239000011521 glass Substances 0.000 description 7
- 229910010272 inorganic material Inorganic materials 0.000 description 7
- 239000011147 inorganic material Substances 0.000 description 7
- 229910052757 nitrogen Inorganic materials 0.000 description 7
- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 description 6
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- 229910004613 CdTe Inorganic materials 0.000 description 5
- 229910052738 indium Inorganic materials 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- SBIBMFFZSBJNJF-UHFFFAOYSA-N selenium;zinc Chemical compound [Se]=[Zn] SBIBMFFZSBJNJF-UHFFFAOYSA-N 0.000 description 5
- 229910052709 silver Inorganic materials 0.000 description 5
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 4
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- 238000001704 evaporation Methods 0.000 description 4
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Natural products NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 3
- MQRWBMAEBQOWAF-UHFFFAOYSA-N acetic acid;nickel Chemical compound [Ni].CC(O)=O.CC(O)=O MQRWBMAEBQOWAF-UHFFFAOYSA-N 0.000 description 3
- 238000006555 catalytic reaction Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- ZBCBWPMODOFKDW-UHFFFAOYSA-N diethanolamine Chemical compound OCCNCCO ZBCBWPMODOFKDW-UHFFFAOYSA-N 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- 238000001493 electron microscopy Methods 0.000 description 3
- 238000002347 injection Methods 0.000 description 3
- 239000007924 injection Substances 0.000 description 3
- 229910044991 metal oxide Inorganic materials 0.000 description 3
- 150000004706 metal oxides Chemical class 0.000 description 3
- 229940078494 nickel acetate Drugs 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 229910052710 silicon Inorganic materials 0.000 description 3
- 239000004332 silver Substances 0.000 description 3
- 238000003980 solgel method Methods 0.000 description 3
- 239000011701 zinc Substances 0.000 description 3
- LQGKDMHENBFVRC-UHFFFAOYSA-N 5-aminopentan-1-ol Chemical compound NCCCCCO LQGKDMHENBFVRC-UHFFFAOYSA-N 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- ZOIORXHNWRGPMV-UHFFFAOYSA-N acetic acid;zinc Chemical compound [Zn].CC(O)=O.CC(O)=O ZOIORXHNWRGPMV-UHFFFAOYSA-N 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 230000001476 alcoholic effect Effects 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000000231 atomic layer deposition Methods 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 239000002800 charge carrier Substances 0.000 description 2
- 239000000084 colloidal system Substances 0.000 description 2
- 239000011258 core-shell material Substances 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 239000002019 doping agent Substances 0.000 description 2
- 238000005401 electroluminescence Methods 0.000 description 2
- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 229910052744 lithium Inorganic materials 0.000 description 2
- 239000002070 nanowire Substances 0.000 description 2
- ZKATWMILCYLAPD-UHFFFAOYSA-N niobium pentoxide Chemical compound O=[Nb](=O)O[Nb](=O)=O ZKATWMILCYLAPD-UHFFFAOYSA-N 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 238000005424 photoluminescence Methods 0.000 description 2
- 238000006068 polycondensation reaction Methods 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 229910052594 sapphire Inorganic materials 0.000 description 2
- 239000010980 sapphire Substances 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- 238000001771 vacuum deposition Methods 0.000 description 2
- 238000007704 wet chemistry method Methods 0.000 description 2
- 239000004246 zinc acetate Substances 0.000 description 2
- YBNMDCCMCLUHBL-UHFFFAOYSA-N (2,5-dioxopyrrolidin-1-yl) 4-pyren-1-ylbutanoate Chemical compound C=1C=C(C2=C34)C=CC3=CC=CC4=CC=C2C=1CCCC(=O)ON1C(=O)CCC1=O YBNMDCCMCLUHBL-UHFFFAOYSA-N 0.000 description 1
- 229910002601 GaN Inorganic materials 0.000 description 1
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- 229910004262 HgTe Inorganic materials 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 229910013504 M-O-M Inorganic materials 0.000 description 1
- 229910002665 PbTe Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 241001455273 Tetrapoda Species 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 150000004703 alkoxides Chemical class 0.000 description 1
- 159000000013 aluminium salts Chemical class 0.000 description 1
- 229910000329 aluminium sulfate Inorganic materials 0.000 description 1
- 230000001680 brushing effect Effects 0.000 description 1
- 229910052792 caesium Inorganic materials 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000001311 chemical methods and process Methods 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000001010 compromised effect Effects 0.000 description 1
- BERDEBHAJNAUOM-UHFFFAOYSA-N copper(I) oxide Inorganic materials [Cu]O[Cu] BERDEBHAJNAUOM-UHFFFAOYSA-N 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- KRFJLUBVMFXRPN-UHFFFAOYSA-N cuprous oxide Chemical compound [O-2].[Cu+].[Cu+] KRFJLUBVMFXRPN-UHFFFAOYSA-N 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000002939 deleterious effect Effects 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
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- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005670 electromagnetic radiation Effects 0.000 description 1
- 238000006056 electrooxidation reaction Methods 0.000 description 1
- 238000000295 emission spectrum Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007717 exclusion Effects 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 229910000078 germane Inorganic materials 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- PJXISJQVUVHSOJ-UHFFFAOYSA-N indium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[In+3].[In+3] PJXISJQVUVHSOJ-UHFFFAOYSA-N 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 238000003913 materials processing Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910001510 metal chloride Inorganic materials 0.000 description 1
- 229910000000 metal hydroxide Inorganic materials 0.000 description 1
- 229910021518 metal oxyhydroxide Inorganic materials 0.000 description 1
- 229910052976 metal sulfide Inorganic materials 0.000 description 1
- 238000002488 metal-organic chemical vapour deposition Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000001451 molecular beam epitaxy Methods 0.000 description 1
- 239000002073 nanorod Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 238000000103 photoluminescence spectrum Methods 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000007650 screen-printing Methods 0.000 description 1
- 150000003346 selenoethers Chemical class 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 230000011664 signaling Effects 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 229910052950 sphalerite Inorganic materials 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- PBCFLUZVCVVTBY-UHFFFAOYSA-N tantalum pentoxide Inorganic materials O=[Ta](=O)O[Ta](=O)=O PBCFLUZVCVVTBY-UHFFFAOYSA-N 0.000 description 1
- OCGWQDWYSQAFTO-UHFFFAOYSA-N tellanylidenelead Chemical compound [Pb]=[Te] OCGWQDWYSQAFTO-UHFFFAOYSA-N 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000007669 thermal treatment Methods 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
- ZNOKGRXACCSDPY-UHFFFAOYSA-N tungsten(VI) oxide Inorganic materials O=[W](=O)=O ZNOKGRXACCSDPY-UHFFFAOYSA-N 0.000 description 1
- YVTHLONGBIQYBO-UHFFFAOYSA-N zinc indium(3+) oxygen(2-) Chemical compound [O--].[Zn++].[In+3] YVTHLONGBIQYBO-UHFFFAOYSA-N 0.000 description 1
- 229910052984 zinc sulfide Inorganic materials 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B33/00—Electroluminescent light sources
- H05B33/10—Apparatus or processes specially adapted to the manufacture of electroluminescent light sources
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/16—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
- H01L33/18—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous within the light emitting region
Definitions
- the present invention relates generally to methods of manufacturing semiconductor devices with p-n junctions including nanocrystals, for instance, quantum-dot light emitting devices ('QD-LEDs').
- the present invention also provides semiconductor devices such as, for instance, QD-LEDs which have been manufactured in an economic fashion in respect of time, cost and processing complexity while affording to the device high efficiency.
- Electronic or “charge carrying” devices formed using semi-conductor materials and including p-n junctions, are commonly used in photovoltaics, diodes, resistors, capacitors, printable electronics and light-emitting devices (LEDs). While such semiconductor devices have been used for some time many devices suffer in terms of sustained operational effectiveness as well as manufacturing simplicity, particularly electronic devices comprising nano-sized crystals or 'dots' (i.e. nanocrystal activated devices). Take for instance quantum-dot based semiconductor devices such as quantum-dot light emitting devices (QD-LEDs) and in particular organic QD-LEDs. Over time the emission quality and lifetime of organic QD-LEDs tend to deteriorate.
- QD-LEDs quantum-dot light emitting devices
- organic QD-LEDs organic QD-LEDs
- nanocrystal - comprising semiconductor devices formed of inorganic materials have been postulated.
- QD-LEDs composed entirely of inorganic materials i.e., inorganic QD-LEDs
- US 6,797,412 and US 2007/0170446 are disclosed in US 6,797,412 and US 2007/0170446.
- US 2007/0170446 is generally directed to inorganic QD-LEDs which comprise an inorganic HTL layer and an inorganic ETL.
- the inorganic HTL layer is deposited on either a (i) sapphire substrate by metal-organic chemical vapour deposition (MOCVD) or (ii) an indium tin oxide substrate (ITO) by vacuum deposition.
- MOCVD metal-organic chemical vapour deposition
- ITO indium tin oxide substrate
- the inorganic ETL layers in examples 1 and 3 were formed using e-beam evaporation (Example 1 , TiO 2 ) and vacuum deposition (Example 3, CdTe).
- inorganic semiconductor devices e.g. QD-LEDs
- a vacuum chamber is necessary for each of the following processes commonly used in the semiconductor industry: chemical vapor deposition, sputtering, e-beam evaporation, molecular-beam epitaxy and atomic layer deposition (ALD);
- chemical vapor deposition, sputtering, e-beam evaporation, molecular-beam epitaxy and atomic layer deposition (ALD) atomic layer deposition
- the present invention provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising the steps of forming the inorganic electron transport layer, inorganic semiconductor nanocrystal layer and inorganic hole transport layer by wet- chemical deposition processes.
- ETL electron transport layer
- HTL inorganic hole transport layer
- the invention provides an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), wherein all three layers are prepared by wet-chemical deposition processes.
- ETL electron transport layer
- HTL inorganic hole transport layer
- the invention is partly based on the discovery that the three main component layers of inorganic semiconductor devices including nanocrystals can all be efficiently and more simply made by inorganic, wet-chemical deposition processes.
- Figure 1 Schematic view of a QD-LED device according to the invention.
- Figure 2 Schematic view of an NiO based QD-LED device according to one embodiment of the invention.
- Figure 3 Schematic view of an NiO based QD-LED device according to another embodiment of the invention.
- Figure 4 Schematic view of an NiO based QD-LED device according to yet another embodiment of the invention.
- Figure 5 Schematic view of an NiO based QD-LED device according to yet another embodiment of the invention.
- Figure 6 Graph showing absorption profile of a NiO based thin film prepared in accordance with an embodiment of the invention.
- Figure 7 Graph showing the current- voltage behaviour of a device according to Example 1.
- Figure 8 Graph showing the spectrum of the electroluminescence measured from the device according to Example 1.
- Figure 9 Graph showing the spectrum of the photo luminescence measured from the device according to Example 1.
- a semiconductor nanocrystal is used in the semiconductor device according to the present invention.
- semiconductor nanocrystal semiconductor nanoparticle
- quantum dot may be used herein interchangeably to refer to any small crystal or particle of a semiconducting material with a diameter less than lOOnm, and preferably less than 20nm. In any case, the particle, diameter is such that the emission properties are functions of the particle's size and shape.
- the size of the crystals or particles used in the semiconductor nanocrystal layer according to the present invention is a feature of this invention and is distinguished from known devices involving phosphor particles and other emissive layers made of substantially larger particles, whose emission properties are not strongly affected by the phosphor particle size.
- nanocrystals One of the unique properties of semiconductor nanocrystals is that the emission from the crystals can be adjusted by variations in the size of the manufactured particles. In some cases further enhancements are possible by preparing the nanoparticles or nanocrystals in the form of rods or wires, by coating them with a second layer or by a combination of the above. Such modified or enhanced nanocrystals are also encompassed by the present invention. This is irrespective of the nomenclature assigned to these materials. For example, quantum rods and quantum wires denote the same type of materials as nanorods and nanowires respectively.
- semiconductor nanocrystals can be grown which exhibit tetrapodal or other complex geometries.
- Such nanowires, nanopods or other designated nanocrystals are considered germane and are envisaged in this invention, provided that one or more dimensions of said nanoparticles or nanocrystals is less than lOOnm, and preferably less than 20nm.
- sol-gel process means a process, which utilises wet- chemical techniques starting from a chemical solution that produces colloidal particles (or sols).
- the sol-gel processes according to the present invention utilise metal alkoxides or metal chlorides, which undergo hydrolysis and polycondensation reactions to form a colloid (i.e., a system composed of solid particles dispersed in a solvent).
- the sol continues on to form an inorganic network containing a liquid phase and gel wherein metal-oxo (M-O-M) or metal-hydroxy (M-OH-M) polymers are formed in solution (referred to herein as 'the precursor sol').
- a drying process serves to remove the liquid phase from the gel thus forming a porous material.
- a thermal treatment (annealing) is often conducted in order to favour further polycondensation and enhance mechanical, optical or electrical properties.
- colloidal nanocrystal film means a material which is also deposited from colloidal particles suspended in a solution, but which is distinct from a sol- gel material in that the particles do not form a gel network during the drying process.
- the particles form a porous solid but retain many of their individual characteristics, as required for example, for retaining the desired emission properties of the quantum dot (QD) layer.
- QD quantum dot
- Deposition of the precursor sol may occur on a substrate to form a layered film by any of the following techniques familiar to those in the field: dip-coating, spin-coating, screen printing, blade coating, brushing, rotational coating, spraying, drop casting or printing.
- the preferred method of film deposition depends on the size and type of the substrate being used and also on the properties of the particular sol being deposited.
- the drying and annealing processes to form the film as described above are thus typically carried out once deposition is completed.
- each layer of the present invention are optimised to maximise conduction of charge through the device and at the same time preserve the emissive properties of the active semiconductor layer. Accordingly, the deposition and annealing of all layers subsequent to deposition of the active layer must be performed at processing temperatures that do not degrade the underlying emissive colloidal nanocrystal film.
- the HTL is deposited via wet-chemical deposition which includes one or more heating stages.
- the precursor sol for the HTL material is formed by dissolving one or more metal salts into a liquid solution to a concentration of between 0.01 and 1.0 M concentration, preferably, 0.1-0.8M, and more preferably 0.3-0.6M.
- Various other chemical additives may be used to enhance stability of the solution or to improve the quality of the film during deposition.
- the film is heated at temperatures high enough to promote formation of a p-type material with high carrier concentration.
- the required temperature for this annealing is in the range of 300 - 1000° C, preferably 300-600 0 C and even more preferably 400-500 0 C.
- the preferred HTL is one which exhibits high transparency (greater than 70%) over the visible wavelength region and which exhibits an electrical resistivity of less than 100 ⁇ cm.
- the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL) 5 said method comprising:
- (i) forming the HTL by wet-chemical deposition including the steps of: (a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
- the semiconductor active layer is also deposited via wet-chemical deposition, which includes a heating stage at a temperature that allows evaporation of the solvent but which is insufficient to physically or chemically degrade the semiconductor nanocrystal components.
- the preferred temperature for this heating is in the range of 50 - 250 0 C, even more preferably 50 - 150 0 C and still even more preferably 50 - 100 0 C.
- the ETL is also deposited via wet-chemical deposition, following which there is included one or more heating stages.
- the precursor sol for the ETL material is formed by dissolving one or more metal salts into a liquid solution to a concentration of between 0.01 and 1.0 M concentration, preferably, 0.1-0.8M, and more preferably 0.3-0.6M.
- Various other chemical additives may be used to enhance stability of the solution or to improve the quality of the film during deposition.
- the precursor sol consists of nanoparticles (formed of the intended ETL material) dispersed in solution.
- the film is heated to promote evaporation of the solvent and optionally cause aggregation of the deposited colloidal material.
- the preferred temperature for this heating is in the range of 50 - 250° C, even more preferably 50 - 150 0 C and still even more preferably 50 - 100 0 C.
- the heating times are from 2-10 minutes.
- the preferred ETL is one which exhibits an electrical resistivity of less than 100 ⁇ cm.
- the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
- the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
- (iii) forming the inorganic ETL by wet-chemical deposition including the steps: (a) preparing a precursor sol by dispersing one or more nanoparticles in a solution; (b) depositing the precursor sol onto a surface; and
- the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
- (i) forming the HTL by wet-chemical deposition including the steps of: (a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
- the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
- the method according to the present invention includes forming the semiconductor nanocrystal layer on the HTL and subsequently forming the ETL on the semiconductor nanocrystal layer.
- the method may also involve first forming the semiconductor nanocrystal layer on the ETL and subsequently forming the HTL on the semiconductor nanocrystal layer.
- reference to a "surface" includes a preformed layer of the device or some other substrate surface.
- the material which may be used in the HTL is composed of an inorganic material capable of transporting holes even in an amorphous state, and is in particular selected from the group comprising NiO, Cu 2 O, SrCu 2 O, and p-ZnO or any combination of these including variations with chemical doping.
- NiO is a particularly preferred inorganic material for forming the HTL layer in respect of the methods of the present invention which utilise wet-chemical processes.
- the present invention also provides an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and a NiO based hole transport layer (HTL), wherein each layer has been prepared by a wet-chemical deposition process.
- ETL electron transport layer
- HTL NiO based hole transport layer
- the HTL layer may consist essentially of NiO or comprise NiO and at least one other inorganic material capable of transporting holes as referred to above, or comprise NiO which has been doped. Suitable dopants include lithium (typically around 1% of atomic composition). NiO is especially preferred for use in the HTL because of the suitability of its valence band energy level, electrical conductivity and the high degree of optical transparency exhibited across the visible region.
- the material which may be used in the inorganic ETL is composed of an inorganic material capable of transporting electrons even in an amorphous state, and in particular an inorganic metal oxide, sulphide or selenide selected from the following n-type semiconductor materials: ZnO, TiO 2 , ZnS, ZnSe, ZrO 2 , SiO 2 , SnO 2 , Ta 2 O 5 , In 2 O 3 , WO 3 ,
- Nb 2 O 5 or any combination of these including variations with chemical doping.
- other metal oxides, oxyhydroxides and hydroxides or mixtures thereof may also be suitable.
- the inorganic material used in the inorganic ETL is ZnO, which includes combinations of ZnO with one or more other suitable n-type semiconductor materials as disclosed above, or ZnO which has been doped. Suitable dopants include Al, Ga and In. ZnO is especially preferred for use in the ETL because of the suitability of its conduction band energy level, electrical conductivity and the low temperature at which a conductive, colloidal nanocrystal film may be formed.
- the present invention provides an inorganic semiconductor device including nanocrystals which comprises a ZnO based inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and a NiO based hole transport layer (HTL), wherein each layer has been prepared by a wet-chemical deposition process.
- ETL inorganic electron transport layer
- HTL NiO based hole transport layer
- the ETL and HTL are deposited from a solution wherein some condensation has already taken place.
- the metal oxide is already in a polymeric, oligomeric or colloidal state prior to deposition.
- the sol precursor solution is heated prior to deposition to ensure the formation of said colloidal particles, whereby the colloid particles in the precursor solution that comprise the ETL or HTL are crystalline prior to deposition.
- the dispersion of the emissive nanocrystals in a sol-gel layer enables other charge carrying devices to be prepared by wet-chemical deposition technologies.
- a further embodiment of this invention is a cell capable of separating charge carriers created by solar insolation or other electromagnetic radiation absorbed by the cell.
- photovoltaic devices are conceived which are prepared by sol-gel methods and comprising nanocrystals embedded in a wide band gap semiconductor matrix.
- the emission from this wet-chemical deposited LED may consist of light emitted by just one nanocrystal.
- the light emitted from a single photon source has distinctive features. It is a property of the present invention that such a single photon source may be realized through a wet-chemically processed device incorporating semiconductor nanocrystals.
- the light emitted by the single nanocrystal can be regulated or modulated by the electrical voltage applied to the device. This feature is fully recognized within this invention. It is a further embodiment that this light emitting structure may be part of a larger functional structure such as a circuit.
- the semiconductor device embodied in this invention may be printed or produced on a continuous basis as part of a larger structure or device.
- an inorganic QD-LED device as prepared by the methods of the present invention may be printed using a roll-to-roll process, enabling large scale production of said LEDs.
- each layer forming the device is characterised by low levels of residual water and/or solvent and more preferably each layer is prepared substantially free of residual water and/or solvent.
- each layer forming the device is characterised by low levels of residual water and/or solvent and more preferably each layer is prepared substantially free of residual water and/or solvent.
- This feature has clear drawbacks in that it is difficult to control the aggregated state of the particles in terms of separation and packing density. It is not possible to prevent pinholes forming, and there are inevitably regions of different particle film thickness. Furthermore such an aggregated state does not permit a well defined resistance to the passage of charge carriers necessary for the efficient operation of the device.
- the method of the present invention may include the step or steps of embedding the particles in a precursor solution and depositing the solution containing the particles by any of the methods previously described, such that the particles are dispersed homogeneously in a matrix of a semiconducting matrix.
- This methodology is illustrated by the following prophetic examples:
- Example A The nanocrystals are dispersed in an ethanolic solution containing ZnO nanocrystals or Zn acetate. The solution is spin coated and dried then annealed. The nanocrystals are dispersed in a thin film of ZnO.
- Example B The nanocrystals are dispersed in an ethanolic solution containing ZnS nanocrystals or Zn acetate and thiourea. The solution is spin coated and dried then annealed. The QDs are dispersed in a thin film of ZnS.
- the conductivity of the matrix can be modified during the creation of the active layer.
- the nanocrystals are dispersed in an ethanolic solution containing ZnO nanocrystals doped with In or Al or the solution contains Zn acetate and an indium or aluminium salt. The solution is spin coated and dried then annealed. The nanocrystals are dispersed in a thin film of In or Al doped ZnO.
- the present invention provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
- step (i) forming the inorganic ETL by a wet-chemical deposition process; (ii) forming the inorganic semiconductor nanocrystal layer by a wet-chemical deposition process which includes the steps: (a) embedding nanoparticles in a precursor solution comprising a semiconducting material; and (b) depositing the precursor solution from step (a) onto a surface such that the nanoparticles are dispersed homogenously in a matrix of the semiconducting material; and (iii) forming the inorganic HTL by a wet-chemical deposition process.
- FIG l is a schematic view showing a preferred embodiment of semiconductor device of the present invention in the form of an inorganic QD-LED.
- an inorganic QD- LED according to the present invention may have a structure including a first electrode 1 as an anode which is formed on a substrate 6, an inorganic HTL 3, a semiconductor nanocrystal layer 2, an inorganic ETL 4 and a second electrode 5.
- a voltage is applied to the first and second metal electrodes 1 and 5
- holes are injected into the HTL 3 from the first electrode, while electrons are injected into the ETL 4 from the second electrode 5.
- the holes and electrons When the holes and electrons are brought into contact with each other in the semiconductor nanocrystals of the semiconductor nanocrystal layer 2, they bind to form excitons, which then recombine, and emit light.
- the light may be in the visible, UV or near IR region. It will be appreciated that the wavelength of the emitted light may be tunable depending on the size of the quantum dots and the nature or make-up of the semiconductor nanocrystal layer.
- the semiconductor nanocrystals used in the semiconductor nanocrystal layer may be selected from any known quantum dot material which has a quantum confinement effect due to size.
- Suitable semiconductor nanocrystals may be made from ZnS, CdS, CdSe, CdTe, ZnSe, ZnTe 5 HgS, HgSe, HgTe, GaN, GaP, GuAs, InP, InAs 5 PbS, PbSe, PbTe and nanocrystals including Si and Ge.
- Other suitable nanocrystals include mixtures of nanocrystals.
- Other suitable nanocrystals include nanocrystals which emit light and which have different shapes, such as rods or tetrapods.
- the nanocrystals include alloys of two or more types of material. Examples include but are not limited to: CdS/CdSe, ZnS/ZnSe, CdS/ZnS, and CdSe/CdTe. It is also possible to tune the emission of a nanocrystal by doping. Examples include the addition of Te to CdSe and Mn ions to CdS or CdSe. Such modified nanocrystals are also considered suitable in the present invention.
- the nanocrystals may be presented in the semiconductor nanocrystal layer in advantageous forms and arrangements.
- the nanocrystals may be presented in the semiconductor nanocrystal layer in the form of core/shell structures such as: CdSe/ZnS, CdSe/ZnSe, CdTe/ZnS, CdTe/ZnSe, CdSe/CdS, CdS/ZnS, CdS/ZeSe, InP/ZnS and PdSe/ZnS, wherein the shell is formed of a semiconductor material having a wider band gap.
- Figure 2 shows an embodiment where the inorganic QD-LED comprises a semiconductor nanocrystal layer 7 where the nanocrystals are of the shell/core type which have been deposited (via a wet-chemical deposition process) onto 3 to form a luminescent thin film.
- Figure 3 shows an embodiment where the inorganic QD-LED comprises a semiconductor nanocrystal layer 8 where the nanocrystals are of the shell/core type which are embedded into a transparent nanocrystal matrix which has been deposited (via a wet-chemical deposition process) onto 3 to form a luminescent thin film.
- Figure 4 shows an embodiment where the inorganic QD-LED comprises a semiconductor nanocrystal layer 10 where the nanocrystals are of the shell/core type and are arranged between and in physical contact with two layers 9 and 11 of semiconductor material having a wider band gap. The layers 9 - 11 are all deposited via a wet-chemical deposition process.
- Figure 5 shows an embodiment wherein the inorganic QD-LED comprises a semiconductor nanocrystal layer 12 wherein the nanocrystals are dispersed in a wide band gap semiconductor material to form a homogeneous distribution of the nanocrystals within the wide band gap semiconductor matrix. This homogeneous layer is also deposited via a wet-chemical deposition process.
- the inorganic QD-LEDs of the present invention may comprise additional functional features including electrodes, transparent substrates, and conductive protective layers.
- 5 represents a metal electrode (cathode) which may be selected from a selection of low- work function metals, including Al, In Mg, Ag, Ca, Li, Cs or alloys thereof.
- 1 also represents a metal electrode (anode) which may be selected from ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), Ni, Pt, Au, Ag, Ir, Pd and oxides thereof.
- the HTL 3 is to be deposited (using a wet-chemical deposition process) on a substrate 1.
- the substrate may be selected from glass, quartz, silicon, GaN, GaAs, sapphire, or other smooth material.
- Example 1 Fabrication of Electroluminescent Diode containing a wet-chemical deposited ETL, OD layer and a wet-chemical deposited HTL
- the QD-LED according to this example is represented by Figure 2 wherein 1 is an ITO layer, 3 is a NiO based HTL layer, 7 is the luminescent QD layer of CdSe/ZnS (core/shell type), 4 is a ZnO ETL layer, 5 is metallic Ag, and 6 is a glass substrate. Fabrication Process:
- a NiO sol-gel precursor solution is made by dissolving Nickel Acetate in propanol to a concentration of 0.4 M, along with an equimolar amount of diethanolamine.
- the sol- gel precursor is deposited onto an ITO coated glass substrate via spin-coating at 3000 rpm for 10 sees.
- the device is then subjected to annealing in air at a temperature of 425° C, forming a transparent HTL layer with a thickness of 50 nm.
- a solution consisting of colloidal CdSe/ZnS core-shell nanocrystals capped with 5- aminopentanol (to render them soluble in alcoholic solvents) dispersed in propanol is prepared. This solution is then deposited on the NiO layer via spin-coating at 3000 rpm for 10 sees. The device is then heated at 100° C for 5 minutes under nitrogen to evaporate the solvent, forming a luminescent thin film with a thickness of 35 nm.
- the nanocrystals were washed twice via repeated precipitation in hexane before being redispersed in fresh ethanol.
- the particle diameter as measured by electron microscopy was between 3-8 nm.
- the solution was deposited on the luminescent QD layer via spin-coating at 3000 rpm for 10 sees. The device is then heated at 100° C for 5 minutes under nitrogen, forming an ETL with a thickness of 40 nm.
- Example 2 Fabrication of Electroluminescent Diode containing a wet-chemical deposited ETL, QD-embedded wet-chemical deposited layer and a wet-chemical deposited HTL
- the QD-LED according to this example is represented by Figure 3 wherein 1 is an ITO layer, 3 is a NiO based HTL layer, 8 is the luminescent QD layer of CdSe/ZnS (core/shell type), 4 is a ZnO ETL layer, 5 is metallic In, and 6 is a glass substrate.
- a NiO sol-gel precursor solution was made by dissolving Nickel Acetate in propanol to a concentration of 0.4 M, along with an equimolar amount of diethanolamine.
- the sol- gel precursor 5 was deposited onto an ITO coated glass substrate via spin-coating at 3000 rpm for 10 sees.
- the device was then subjected to annealing in air at a temperature of 425° C, forming a transparent HTL layer with a thickness of 50 nm.
- a ZnS sol-gel precursor solution was made by dissolving Zinc Acetate and thiourea in a propanol/water mixture (ratio 6:1) to a concentration of 0.1 M. To this solution, QDs dispersed in propanol are added and the combined solution was deposited on the NiO layer via spin-coating at 3000 rpm for 10 sees. The device was then heated at 100° C for 5 minutes under nitrogen to evaporate the solvent, forming a luminescent thin film with a thickness of 100 nm. The layer thus formed consists of colloidal QDs homogenously dispersed into a transparent, ZnS matrix.
- Example 3 Fabrication of Electroluminescent Diode containing a wet-chemical deposited ETL, 1 st wide-bandgap sol-gel layer, QD layer, 2 nd wide-bandgap sol-gel layer and wet-chemical deposited HTL
- the QD-LED according to this example was represented by Figure 4 wherein 1 was an ITO layer, 3 was a NiO based HTL layer, 9 represents the luminescent QD layer of CdSe/ZnS (core/shell type), 10 and 11 represent ZnS layers, 4 was a ZnO ETL layer, 5 was metallic Ag, and 6 was a glass substrate.
- a NiO sol-gel precursor solution was made by dissolving Nickel Acetate in propanol to a concentration of 0.4 M, along with an equimolar amount of diethanolamine.
- the sol- gel precursor 5 was deposited onto an ITO coated glass substrate via spin-coating at 3000 rpm for 10 sees.
- the device was then subjected to annealing in air at a temperature of 425° C, forming a transparent HTL layer with a thickness of 50 nm.
- a ZnS sol-gel precursor solution was made by dissolving Zinc Acetate and thiourea in a propanol/water mixture (ratio 6:1) to a concentration of 0.05 M.
- a layer of ZnS was deposited via spin-coating at 3000 rpm for 10 sees, forming an intermediate layer between the HTL and the luminescent layer. This layer was 10 nm in thickness.
- a solution consisting of colloidal CdSe/ZnS core-shell nanocrystals capped with 5- aminopentanol (to render them soluble in alcoholic solvents) dispersed in propanol was prepared. This solution was then deposited on the NiO layer via spin-coating at 3000 rpm for 10 sees. The device was then heated at 100° C for 5 minutes under nitrogen to evaporate the solvent, forming a luminescent thin film with a thickness of 35 ran.
- a second layer of ZnS was deposited via spin- coating at 3000 rpm for 10 sees, forming an intermediate layer between the luminescent layer and the ETL. This layer was 10 nm in thickness.
- the graph in Figure 6 showing an absorption profile of the NiO thin film material prepared using the methods described above.
- the material is highly transparent over the visible region and is therefore highly suitable as a HTL in a QD-LED.
- the line labeled Device B shows the current- voltage behaviour of an alternate device which is otherwise identical to Example 1 but which has the ETL omitted.
- the inclusion of the ETL clearly enhances the injection of electrons into the active layer, as evidenced by the reduced turn-on voltage and improved current flow.
- the graph in Figure 8 shows the spectrum of the photoluminescence and electroluminescence measured from the device described in Example 1.
- the dashed line represents the photoluminescence spectrum, showing contributions from both the active layer and from the ZnO contained in the ETL are visible in the emission spectrum.
- the solid line represents the electroluminsecence spectrum, showing pure emissions from the active layer.
- the graph in Figure 9 shows a plot of the luminous intensity as a function of applied voltage for the device described in Example 1. The measurements were made under ambient conditions with the light intensity measured via a calibrated silicon photodiode.
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Abstract
The present invention relates generally to methods of manufacturing semiconductor devices with p-n junctions including nanocrystals, for instance, quantum-dot light emitting devices ('QD-LEDs'). The present invention also provides semiconductor devices such as, for instance, QD-LEDs which have been manufactured in an economic fashion in respect of time, cost and processing complexity while affording to the device high efficiency.
Description
SEMICONDUCTOR DEVICE INCLUDING NANOCRYST ALS AND METHODS OF MANUFACTURING THE SAME
Field of the Invention
The present invention relates generally to methods of manufacturing semiconductor devices with p-n junctions including nanocrystals, for instance, quantum-dot light emitting devices ('QD-LEDs'). The present invention also provides semiconductor devices such as, for instance, QD-LEDs which have been manufactured in an economic fashion in respect of time, cost and processing complexity while affording to the device high efficiency.
Background of the Invention
Electronic or "charge carrying" devices, formed using semi-conductor materials and including p-n junctions, are commonly used in photovoltaics, diodes, resistors, capacitors, printable electronics and light-emitting devices (LEDs). While such semiconductor devices have been used for some time many devices suffer in terms of sustained operational effectiveness as well as manufacturing simplicity, particularly electronic devices comprising nano-sized crystals or 'dots' (i.e. nanocrystal activated devices). Take for instance quantum-dot based semiconductor devices such as quantum-dot light emitting devices (QD-LEDs) and in particular organic QD-LEDs. Over time the emission quality and lifetime of organic QD-LEDs tend to deteriorate. This is typically attributed to the degradation of the organic based luminescent materials used. For instance, US 2004/0023010 discloses organic QD-LEDs where the electron transport layer (ETL) (also known as the electron-injection layer) and the hole transport layer (HTL) (also known as the hole-injection layer) are presented in the form of organic based thin films. The active luminescent layer in these QD-LEDs is inorganic in nature. In these layers organic/inorganic interfacial defects arise over time because the organic based thin films are in physical contact with the luminescent layer. Ensuring the stability of such devices is additionally compromised over time because the organic film layers tend to degrade upon exposure to atmospheric air and/or moisture. To overcome such degradation the organic
components of these QD-LEDs are often encapsulated. Also, during the fabrication of these organic QD-LEDs great expense and care is usually taken to ensure the manufacturing process is conducted in an oxygen and nitrogen free environment.
In an attempt to address the above problems nanocrystal - comprising semiconductor devices formed of inorganic materials have been postulated. For example, QD-LEDs composed entirely of inorganic materials (i.e., inorganic QD-LEDs) are disclosed in US 6,797,412 and US 2007/0170446.
US 2007/0170446 is generally directed to inorganic QD-LEDs which comprise an inorganic HTL layer and an inorganic ETL. In the examples, the inorganic HTL layer is deposited on either a (i) sapphire substrate by metal-organic chemical vapour deposition (MOCVD) or (ii) an indium tin oxide substrate (ITO) by vacuum deposition. The inorganic ETL layers in examples 1 and 3 were formed using e-beam evaporation (Example 1 , TiO2) and vacuum deposition (Example 3, CdTe).
For the economical fabrication of inorganic semiconductor devices (e.g. QD-LEDs), it is desirable to avoid the use of techniques involving a vacuum chamber. The use of a vacuum chamber is necessary for each of the following processes commonly used in the semiconductor industry: chemical vapor deposition, sputtering, e-beam evaporation, molecular-beam epitaxy and atomic layer deposition (ALD); The slow and cumbersome nature of materials-processing within a vacuum chamber increases the cost of manufacturing and also places practical limits on both the physical dimensions and the types of devices that can be made.
Accordingly, there is a need for semiconductor devices which can offer tunable emission wavelengths which can be fabricated using efficient process methodology wherein said devices are comprised of photostable and chemically robust materials.
Summary of Invention
The present invention provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising the steps of forming the inorganic electron transport layer, inorganic semiconductor nanocrystal layer and inorganic hole transport layer by wet- chemical deposition processes.
In a further aspect the invention provides an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), wherein all three layers are prepared by wet-chemical deposition processes.
The invention is partly based on the discovery that the three main component layers of inorganic semiconductor devices including nanocrystals can all be efficiently and more simply made by inorganic, wet-chemical deposition processes.
Brief Description of the Drawings
Figure 1 : Schematic view of a QD-LED device according to the invention.
Figure 2: Schematic view of an NiO based QD-LED device according to one embodiment of the invention.
Figure 3: Schematic view of an NiO based QD-LED device according to another embodiment of the invention.
Figure 4: Schematic view of an NiO based QD-LED device according to yet another embodiment of the invention.
Figure 5: Schematic view of an NiO based QD-LED device according to yet another embodiment of the invention.
Figure 6: Graph showing absorption profile of a NiO based thin film prepared in accordance with an embodiment of the invention.
Figure 7: Graph showing the current- voltage behaviour of a device according to Example 1.
Figure 8: Graph showing the spectrum of the electroluminescence measured from the device according to Example 1.
Figure 9: Graph showing the spectrum of the photo luminescence measured from the device according to Example 1.
Detailed Description of the Invention
A semiconductor nanocrystal is used in the semiconductor device according to the present invention. The terms "semiconductor nanocrystal", "semiconductor nanoparticle" and "quantum dot" may be used herein interchangeably to refer to any small crystal or particle of a semiconducting material with a diameter less than lOOnm, and preferably less than 20nm. In any case, the particle, diameter is such that the emission properties are functions of the particle's size and shape. The size of the crystals or particles used in the semiconductor nanocrystal layer according to the present invention is a feature of this invention and is distinguished from known devices involving phosphor particles and other emissive layers made of substantially larger particles, whose emission properties are not strongly affected by the phosphor particle size.
One of the unique properties of semiconductor nanocrystals is that the emission from the crystals can be adjusted by variations in the size of the manufactured particles. In some cases further enhancements are possible by preparing the nanoparticles or nanocrystals in
the form of rods or wires, by coating them with a second layer or by a combination of the above. Such modified or enhanced nanocrystals are also encompassed by the present invention. This is irrespective of the nomenclature assigned to these materials. For example, quantum rods and quantum wires denote the same type of materials as nanorods and nanowires respectively.
It is further found that semiconductor nanocrystals can be grown which exhibit tetrapodal or other complex geometries. Such nanowires, nanopods or other designated nanocrystals are considered germane and are envisaged in this invention, provided that one or more dimensions of said nanoparticles or nanocrystals is less than lOOnm, and preferably less than 20nm.
As used herein, reference to a "sol-gel process" means a process, which utilises wet- chemical techniques starting from a chemical solution that produces colloidal particles (or sols). Preferably, the sol-gel processes according to the present invention utilise metal alkoxides or metal chlorides, which undergo hydrolysis and polycondensation reactions to form a colloid (i.e., a system composed of solid particles dispersed in a solvent). The sol continues on to form an inorganic network containing a liquid phase and gel wherein metal-oxo (M-O-M) or metal-hydroxy (M-OH-M) polymers are formed in solution (referred to herein as 'the precursor sol'). A drying process serves to remove the liquid phase from the gel thus forming a porous material. A thermal treatment (annealing) is often conducted in order to favour further polycondensation and enhance mechanical, optical or electrical properties.
As used herein reference to "colloidal nanocrystal film" means a material which is also deposited from colloidal particles suspended in a solution, but which is distinct from a sol- gel material in that the particles do not form a gel network during the drying process. The particles form a porous solid but retain many of their individual characteristics, as required for example, for retaining the desired emission properties of the quantum dot (QD) layer.
The deposition processes to form the layers of the inorganic semiconductor device of the present invention are all based on either of the two above described methodologies, which are collectively referred to herein as "wet-chemical deposition". Deposition of the precursor sol may occur on a substrate to form a layered film by any of the following techniques familiar to those in the field: dip-coating, spin-coating, screen printing, blade coating, brushing, rotational coating, spraying, drop casting or printing. The preferred method of film deposition depends on the size and type of the substrate being used and also on the properties of the particular sol being deposited. The drying and annealing processes to form the film as described above are thus typically carried out once deposition is completed.
The preferred processing parameters of each layer of the present invention are optimised to maximise conduction of charge through the device and at the same time preserve the emissive properties of the active semiconductor layer. Accordingly, the deposition and annealing of all layers subsequent to deposition of the active layer must be performed at processing temperatures that do not degrade the underlying emissive colloidal nanocrystal film.
Preferred processing ranges for each of the HTL, active semiconductor layer and ETL are as follows:
The HTL is deposited via wet-chemical deposition which includes one or more heating stages. The precursor sol for the HTL material is formed by dissolving one or more metal salts into a liquid solution to a concentration of between 0.01 and 1.0 M concentration, preferably, 0.1-0.8M, and more preferably 0.3-0.6M. Various other chemical additives may be used to enhance stability of the solution or to improve the quality of the film during deposition. After deposition, the film is heated at temperatures high enough to promote formation of a p-type material with high carrier concentration. The required temperature for this annealing is in the range of 300 - 1000° C, preferably 300-600 0C and even more preferably 400-500 0C.
The preferred HTL is one which exhibits high transparency (greater than 70%) over the visible wavelength region and which exhibits an electrical resistivity of less than 100 Ω cm.
In an embodiment the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL)5 said method comprising:
(i) forming the HTL by wet-chemical deposition including the steps of: (a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the HTL; (ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and (iii) forming the ETL by wet-chemical deposition.
The semiconductor active layer is also deposited via wet-chemical deposition, which includes a heating stage at a temperature that allows evaporation of the solvent but which is insufficient to physically or chemically degrade the semiconductor nanocrystal components. The preferred temperature for this heating is in the range of 50 - 250 0C, even more preferably 50 - 150 0C and still even more preferably 50 - 100 0C.
The ETL is also deposited via wet-chemical deposition, following which there is included one or more heating stages. The precursor sol for the ETL material is formed by dissolving one or more metal salts into a liquid solution to a concentration of between 0.01 and 1.0 M concentration, preferably, 0.1-0.8M, and more preferably 0.3-0.6M. Various other chemical additives may be used to enhance stability of the solution or to improve the quality of the film during deposition. Alternatively, the precursor sol consists of nanoparticles (formed of the intended ETL material) dispersed in solution. After
deposition, the film is heated to promote evaporation of the solvent and optionally cause aggregation of the deposited colloidal material. The preferred temperature for this heating is in the range of 50 - 250° C, even more preferably 50 - 150 0C and still even more preferably 50 - 100 0C. Preferably the heating times are from 2-10 minutes.
The preferred ETL is one which exhibits an electrical resistivity of less than 100 Ω cm.
In an embodiment the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the inorganic HTL by wet-chemical deposition;
(ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and (iii) forming the inorganic ETL by wet-chemical deposition including the steps:
(a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
In an embodiment the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the inorganic HTL by wet-chemical deposition;
(ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and
(iii) forming the inorganic ETL by wet-chemical deposition including the steps: (a) preparing a precursor sol by dispersing one or more nanoparticles in a solution;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
In an embodiment the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the HTL by wet-chemical deposition including the steps of: (a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the HTL; (ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and (iii) forming the inorganic ETL by wet-chemical deposition including the steps:
(a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M; (b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
In an embodiment the invention also provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the HTL by wet-chemical deposition including the steps of:
(a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the HTL;
(ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and (iii) forming the inorganic ETL by wet-chemical deposition including the steps:
(d) preparing a precursor sol by dispensing one or more nanoparticles in a solution;
(e) depositing the precursor sol onto a surface; and
(f) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
The method according to the present invention as illustrated for instance in the above embodiments, includes forming the semiconductor nanocrystal layer on the HTL and subsequently forming the ETL on the semiconductor nanocrystal layer. As an alternative the method may also involve first forming the semiconductor nanocrystal layer on the ETL and subsequently forming the HTL on the semiconductor nanocrystal layer. Accordingly, in the embodiments referred to above it will be appreciated that reference to a "surface" includes a preformed layer of the device or some other substrate surface.
The material which may be used in the HTL is composed of an inorganic material capable of transporting holes even in an amorphous state, and is in particular selected from the group comprising NiO, Cu2O, SrCu2O, and p-ZnO or any combination of these including variations with chemical doping. In relation to conductive quality and optical transparency (in respect of the resultant emitted light from a QD-LED for instance) it has been found that NiO is a particularly preferred inorganic material for forming the HTL layer in respect of the methods of the present invention which utilise wet-chemical processes.
Accordingly, the present invention also provides an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and a NiO based hole transport layer (HTL), wherein each layer has been prepared by a wet-chemical deposition process.
As referred to above "NiO based" means that the HTL layer may consist essentially of NiO or comprise NiO and at least one other inorganic material capable of transporting holes as referred to above, or comprise NiO which has been doped. Suitable dopants include lithium (typically around 1% of atomic composition). NiO is especially preferred for use in the HTL because of the suitability of its valence band energy level, electrical conductivity and the high degree of optical transparency exhibited across the visible region.
The material which may be used in the inorganic ETL is composed of an inorganic material capable of transporting electrons even in an amorphous state, and in particular an inorganic metal oxide, sulphide or selenide selected from the following n-type semiconductor materials: ZnO, TiO2, ZnS, ZnSe, ZrO2, SiO2, SnO2, Ta2O5, In2O3, WO3,
Nb2O5 or any combination of these including variations with chemical doping. However, other metal oxides, oxyhydroxides and hydroxides or mixtures thereof may also be suitable.
Preferably the inorganic material used in the inorganic ETL is ZnO, which includes combinations of ZnO with one or more other suitable n-type semiconductor materials as disclosed above, or ZnO which has been doped. Suitable dopants include Al, Ga and In. ZnO is especially preferred for use in the ETL because of the suitability of its conduction band energy level, electrical conductivity and the low temperature at which a conductive, colloidal nanocrystal film may be formed.
Accordingly, in an even more preferred embodiment the present invention provides an inorganic semiconductor device including nanocrystals which comprises a ZnO based inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and a NiO based hole transport layer (HTL), wherein each layer has been prepared by a wet-chemical deposition process.
In another embodiment, the ETL and HTL are deposited from a solution wherein some condensation has already taken place. In this solution, the metal oxide is already in a polymeric, oligomeric or colloidal state prior to deposition.
In yet another embodiment, the sol precursor solution is heated prior to deposition to ensure the formation of said colloidal particles, whereby the colloid particles in the precursor solution that comprise the ETL or HTL are crystalline prior to deposition.
It is a further feature of this invention that the dispersion of the emissive nanocrystals in a sol-gel layer enables other charge carrying devices to be prepared by wet-chemical deposition technologies. For example, a further embodiment of this invention is a cell capable of separating charge carriers created by solar insolation or other electromagnetic radiation absorbed by the cell. Thus photovoltaic devices are conceived which are prepared by sol-gel methods and comprising nanocrystals embedded in a wide band gap semiconductor matrix.
It is recognized that by the emission of tunable light using a wet-chemical deposited LED that near infra-red and infra-red light may be emitted. This is useful in other applications such as lamps, signalling devices, communication devices, alarms, sensors and actuators in which the nanocrystals emit radiation of a specified wavelength upon application of an electronic input signal.
It is further envisaged that the emission from this wet-chemical deposited LED may consist of light emitted by just one nanocrystal. The light emitted from a single photon source has distinctive features. It is a property of the present invention that such a single photon source may be realized through a wet-chemically processed device incorporating semiconductor nanocrystals.
It is further envisaged that the light emitted by the single nanocrystal can be regulated or modulated by the electrical voltage applied to the device. This feature is fully recognized within this invention.
It is a further embodiment that this light emitting structure may be part of a larger functional structure such as a circuit.
It is also recognized that the semiconductor device embodied in this invention may be printed or produced on a continuous basis as part of a larger structure or device. For example, an inorganic QD-LED device as prepared by the methods of the present invention may be printed using a roll-to-roll process, enabling large scale production of said LEDs.
In particular embodiments each layer forming the device is characterised by low levels of residual water and/or solvent and more preferably each layer is prepared substantially free of residual water and/or solvent. Those skilled in the art may appreciate the advantages conferred by having low levels of residual water and/or solvent in respect of, for instance, minimising electrochemical corrosion and hence maintaining high quantum efficiency over the operational lifetime of the device.
It is a feature of current QD-LED structures that the nanocrystals are deposited onto an ETL or HTL from a solution and then dried to form a film of aggregated particles. This feature is indeed common to all extant devices and inventions.
This feature has clear drawbacks in that it is difficult to control the aggregated state of the particles in terms of separation and packing density. It is not possible to prevent pinholes forming, and there are inevitably regions of different particle film thickness. Furthermore such an aggregated state does not permit a well defined resistance to the passage of charge carriers necessary for the efficient operation of the device.
In a further embodiment of this invention, the method of the present invention may include the step or steps of embedding the particles in a precursor solution and depositing the solution containing the particles by any of the methods previously described, such that the particles are dispersed homogeneously in a matrix of a semiconducting matrix.
This methodology is illustrated by the following prophetic examples:
Example A The nanocrystals are dispersed in an ethanolic solution containing ZnO nanocrystals or Zn acetate. The solution is spin coated and dried then annealed. The nanocrystals are dispersed in a thin film of ZnO.
Example B The nanocrystals are dispersed in an ethanolic solution containing ZnS nanocrystals or Zn acetate and thiourea. The solution is spin coated and dried then annealed. The QDs are dispersed in a thin film of ZnS.
The advantage of this wet-chemical synthesis of the active layer over existing methods is evident. The QDs are embedded in a homogeneous environment. Their concentration and the film thickness can be regulated. This new method provides for a pinhole free, crack- free layer whose resistivity can be controlled and in which the nanocrystals are isolated from the deleterious effects of the environment, including oxygen and water.
Example C
The conductivity of the matrix can be modified during the creation of the active layer. The nanocrystals are dispersed in an ethanolic solution containing ZnO nanocrystals doped with In or Al or the solution contains Zn acetate and an indium or aluminium salt. The solution is spin coated and dried then annealed. The nanocrystals are dispersed in a thin film of In or Al doped ZnO.
Accordingly, in another embodiment the present invention provides a method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the inorganic ETL by a wet-chemical deposition process;
(ii) forming the inorganic semiconductor nanocrystal layer by a wet-chemical deposition process which includes the steps: (a) embedding nanoparticles in a precursor solution comprising a semiconducting material; and (b) depositing the precursor solution from step (a) onto a surface such that the nanoparticles are dispersed homogenously in a matrix of the semiconducting material; and (iii) forming the inorganic HTL by a wet-chemical deposition process.
Figure l is a schematic view showing a preferred embodiment of semiconductor device of the present invention in the form of an inorganic QD-LED. As shown, an inorganic QD- LED according to the present invention may have a structure including a first electrode 1 as an anode which is formed on a substrate 6, an inorganic HTL 3, a semiconductor nanocrystal layer 2, an inorganic ETL 4 and a second electrode 5. When a voltage is applied to the first and second metal electrodes 1 and 5, holes are injected into the HTL 3 from the first electrode, while electrons are injected into the ETL 4 from the second electrode 5. When the holes and electrons are brought into contact with each other in the semiconductor nanocrystals of the semiconductor nanocrystal layer 2, they bind to form excitons, which then recombine, and emit light. The light may be in the visible, UV or near IR region. It will be appreciated that the wavelength of the emitted light may be tunable depending on the size of the quantum dots and the nature or make-up of the semiconductor nanocrystal layer.
Thus the semiconductor nanocrystals used in the semiconductor nanocrystal layer may be selected from any known quantum dot material which has a quantum confinement effect due to size. Suitable semiconductor nanocrystals may be made from ZnS, CdS, CdSe, CdTe, ZnSe, ZnTe5 HgS, HgSe, HgTe, GaN, GaP, GuAs, InP, InAs5 PbS, PbSe, PbTe and nanocrystals including Si and Ge. Other suitable nanocrystals include mixtures of nanocrystals.
Other suitable nanocrystals include nanocrystals which emit light and which have different shapes, such as rods or tetrapods. Furthermore, it is envisaged that the nanocrystals include alloys of two or more types of material. Examples include but are not limited to: CdS/CdSe, ZnS/ZnSe, CdS/ZnS, and CdSe/CdTe. It is also possible to tune the emission of a nanocrystal by doping. Examples include the addition of Te to CdSe and Mn ions to CdS or CdSe. Such modified nanocrystals are also considered suitable in the present invention.
Using the wet-chemical processes described herein the nanocrystals may be presented in the semiconductor nanocrystal layer in advantageous forms and arrangements. For instance, the nanocrystals may be presented in the semiconductor nanocrystal layer in the form of core/shell structures such as: CdSe/ZnS, CdSe/ZnSe, CdTe/ZnS, CdTe/ZnSe, CdSe/CdS, CdS/ZnS, CdS/ZeSe, InP/ZnS and PdSe/ZnS, wherein the shell is formed of a semiconductor material having a wider band gap.
For instance, Figure 2 shows an embodiment where the inorganic QD-LED comprises a semiconductor nanocrystal layer 7 where the nanocrystals are of the shell/core type which have been deposited (via a wet-chemical deposition process) onto 3 to form a luminescent thin film.
As an alternative, Figure 3 shows an embodiment where the inorganic QD-LED comprises a semiconductor nanocrystal layer 8 where the nanocrystals are of the shell/core type which are embedded into a transparent nanocrystal matrix which has been deposited (via a wet-chemical deposition process) onto 3 to form a luminescent thin film.
As a further alternative, Figure 4 shows an embodiment where the inorganic QD-LED comprises a semiconductor nanocrystal layer 10 where the nanocrystals are of the shell/core type and are arranged between and in physical contact with two layers 9 and 11 of semiconductor material having a wider band gap. The layers 9 - 11 are all deposited via a wet-chemical deposition process.
As a still further preferred embodiment, Figure 5 shows an embodiment wherein the inorganic QD-LED comprises a semiconductor nanocrystal layer 12 wherein the nanocrystals are dispersed in a wide band gap semiconductor material to form a homogeneous distribution of the nanocrystals within the wide band gap semiconductor matrix. This homogeneous layer is also deposited via a wet-chemical deposition process.
It will be appreciated from the figures that the inorganic QD-LEDs of the present invention may comprise additional functional features including electrodes, transparent substrates, and conductive protective layers. For instance, in Figures 1 to 5, 5 represents a metal electrode (cathode) which may be selected from a selection of low- work function metals, including Al, In Mg, Ag, Ca, Li, Cs or alloys thereof. Also, as shown in the Figures, 1 also represents a metal electrode (anode) which may be selected from ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), Ni, Pt, Au, Ag, Ir, Pd and oxides thereof. Also, from the Figures it is contemplated that the HTL 3 is to be deposited (using a wet-chemical deposition process) on a substrate 1. The substrate may be selected from glass, quartz, silicon, GaN, GaAs, sapphire, or other smooth material.
Certain embodiments of the invention will now be described with reference to the following examples which are intended for the purpose of illustration only and are not intended to limit the scope of the generality hereinbefore described.
Examples
Example 1 - Fabrication of Electroluminescent Diode containing a wet-chemical deposited ETL, OD layer and a wet-chemical deposited HTL
The QD-LED according to this example is represented by Figure 2 wherein 1 is an ITO layer, 3 is a NiO based HTL layer, 7 is the luminescent QD layer of CdSe/ZnS (core/shell type), 4 is a ZnO ETL layer, 5 is metallic Ag, and 6 is a glass substrate.
Fabrication Process:
1. A NiO sol-gel precursor solution is made by dissolving Nickel Acetate in propanol to a concentration of 0.4 M, along with an equimolar amount of diethanolamine. The sol- gel precursor is deposited onto an ITO coated glass substrate via spin-coating at 3000 rpm for 10 sees. The device is then subjected to annealing in air at a temperature of 425° C, forming a transparent HTL layer with a thickness of 50 nm.
2. A solution consisting of colloidal CdSe/ZnS core-shell nanocrystals capped with 5- aminopentanol (to render them soluble in alcoholic solvents) dispersed in propanol is prepared. This solution is then deposited on the NiO layer via spin-coating at 3000 rpm for 10 sees. The device is then heated at 100° C for 5 minutes under nitrogen to evaporate the solvent, forming a luminescent thin film with a thickness of 35 nm.
3. A solution consisting of colloidal ZnO nanocrystals dispersed in ethanol (concentration 0.1 M) is prepared via a low temperature base-catalyzed reaction well described in the literature. The nanocrystals were washed twice via repeated precipitation in hexane before being redispersed in fresh ethanol. The particle diameter as measured by electron microscopy was between 3-8 nm. The solution was deposited on the luminescent QD layer via spin-coating at 3000 rpm for 10 sees. The device is then heated at 100° C for 5 minutes under nitrogen, forming an ETL with a thickness of 40 nm.
4. Metallic silver is then deposited on the ZnO layer through a patterned mask to form the device cathode.
Example 2 - Fabrication of Electroluminescent Diode containing a wet-chemical deposited ETL, QD-embedded wet-chemical deposited layer and a wet-chemical deposited HTL
The QD-LED according to this example is represented by Figure 3 wherein 1 is an ITO layer, 3 is a NiO based HTL layer, 8 is the luminescent QD layer of CdSe/ZnS (core/shell type), 4 is a ZnO ETL layer, 5 is metallic In, and 6 is a glass substrate.
Fabrication Process:
1. A NiO sol-gel precursor solution was made by dissolving Nickel Acetate in propanol to a concentration of 0.4 M, along with an equimolar amount of diethanolamine. The sol- gel precursor 5 was deposited onto an ITO coated glass substrate via spin-coating at 3000 rpm for 10 sees. The device was then subjected to annealing in air at a temperature of 425° C, forming a transparent HTL layer with a thickness of 50 nm.
2. A ZnS sol-gel precursor solution was made by dissolving Zinc Acetate and thiourea in a propanol/water mixture (ratio 6:1) to a concentration of 0.1 M. To this solution, QDs dispersed in propanol are added and the combined solution was deposited on the NiO layer via spin-coating at 3000 rpm for 10 sees. The device was then heated at 100° C for 5 minutes under nitrogen to evaporate the solvent, forming a luminescent thin film with a thickness of 100 nm. The layer thus formed consists of colloidal QDs homogenously dispersed into a transparent, ZnS matrix.
3. A solution consisting of colloidal ZnO nanocrystals dispersed in ethanol (concentration 0.1 M) was prepared via a low temperature base-catalyzed reaction well described in the literature. The nanocrystals were washed twice via repeated precipitation in hexane before being redispersed in fresh ethanol. The particle diameter as measured by electron microscopy was between 3-8 nm. The solution was deposited on the luminescent QD-ZnS layer via spin-coating at 3000 rpm for 10 sees. The device was then heated at 100° C for 5 minutes under nitrogen, forming an ETL with a thickness of 40 nm.
4. Metallic silver was then deposited on the ZnO layer through a patterned mask to form the device cathode.
Example 3 - Fabrication of Electroluminescent Diode containing a wet-chemical deposited ETL, 1st wide-bandgap sol-gel layer, QD layer, 2nd wide-bandgap sol-gel layer and wet-chemical deposited HTL
The QD-LED according to this example was represented by Figure 4 wherein 1 was an ITO layer, 3 was a NiO based HTL layer, 9 represents the luminescent QD layer of CdSe/ZnS (core/shell type), 10 and 11 represent ZnS layers, 4 was a ZnO ETL layer, 5 was metallic Ag, and 6 was a glass substrate.
Fabrication Process:
1. A NiO sol-gel precursor solution was made by dissolving Nickel Acetate in propanol to a concentration of 0.4 M, along with an equimolar amount of diethanolamine. The sol- gel precursor 5 was deposited onto an ITO coated glass substrate via spin-coating at 3000 rpm for 10 sees. The device was then subjected to annealing in air at a temperature of 425° C, forming a transparent HTL layer with a thickness of 50 nm.
2. A ZnS sol-gel precursor solution was made by dissolving Zinc Acetate and thiourea in a propanol/water mixture (ratio 6:1) to a concentration of 0.05 M. On the NiO thin film, a layer of ZnS was deposited via spin-coating at 3000 rpm for 10 sees, forming an intermediate layer between the HTL and the luminescent layer. This layer was 10 nm in thickness.
3. A solution consisting of colloidal CdSe/ZnS core-shell nanocrystals capped with 5- aminopentanol (to render them soluble in alcoholic solvents) dispersed in propanol was prepared. This solution was then deposited on the NiO layer via spin-coating at 3000 rpm
for 10 sees. The device was then heated at 100° C for 5 minutes under nitrogen to evaporate the solvent, forming a luminescent thin film with a thickness of 35 ran.
4. On the luminescent QD thin film, a second layer of ZnS was deposited via spin- coating at 3000 rpm for 10 sees, forming an intermediate layer between the luminescent layer and the ETL. This layer was 10 nm in thickness.
5. A solution consisting of colloidal ZnO nanocrystals dispersed in ethanol (concentration 0.1 M) was prepared via a low temperature base-catalyzed reaction well described in the literature The nanocrystals were washed twice via repeated precipitation in hexane before being redispersed in fresh ethanol. The particle diameter as measured by electron microscopy was between 3-8 nm. The solution was deposited on the luminescent QD layer via spin-coating at 3000 rpm for 10 sees. The device was then heated at 100° C for 5 minutes under nitrogen, forming an ETL with a thickness of 40 nm.
6. Metallic silver was then deposited on the ZnO layer through a patterned mask to form the device cathode.
Device Testing and Performance
The graph in Figure 6 showing an absorption profile of the NiO thin film material prepared using the methods described above. The material is highly transparent over the visible region and is therefore highly suitable as a HTL in a QD-LED.
The graph in Figure 7 with the line labeled Device A showing the current-voltage behaviour of the device described in Example 1. The line labeled Device B shows the current- voltage behaviour of an alternate device which is otherwise identical to Example 1 but which has the ETL omitted. The inclusion of the ETL clearly enhances the injection of electrons into the active layer, as evidenced by the reduced turn-on voltage and improved current flow.
The graph in Figure 8 shows the spectrum of the photoluminescence and electroluminescence measured from the device described in Example 1. The dashed line represents the photoluminescence spectrum, showing contributions from both the active layer and from the ZnO contained in the ETL are visible in the emission spectrum. The solid line represents the electroluminsecence spectrum, showing pure emissions from the active layer.
The graph in Figure 9 shows a plot of the luminous intensity as a function of applied voltage for the device described in Example 1. The measurements were made under ambient conditions with the light intensity measured via a calibrated silicon photodiode.
The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
Claims
1. A method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising the steps of forming the inorganic electron transport layer, inorganic semiconductor nanocrystal layer and inorganic hole transport layer by wet-chemical deposition processes.
2. A method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the HTL by wet-chemical deposition including the steps of: (a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the HTL; (ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and (iii) forming the ETL by wet-chemical deposition.
3. A method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the inorganic HTL by wet-chemical deposition;
(ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and
(iii) forming the inorganic ETL by wet-chemical deposition including the steps: (a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
4. A method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the inorganic HTL by wet-chemical deposition;
(ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and
(iii) forming the inorganic ETL by wet-chemical deposition including the steps: (a) preparing a precursor sol by dispersing one or more nanoparticles in a solution;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
5. A method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising: (i) forming the HTL by wet-chemical deposition including the steps of:
(a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to l.OM;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the HTL; (ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and (iii) forming the inorganic ETL by wet-chemical deposition including the steps:
(a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
6. A method of manufacturing an inorganic semiconductor device including nanocrystals which comprises an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an inorganic hole transport layer (HTL), said method comprising:
(i) forming the HTL by wet-chemical deposition including the steps of: (a) preparing a precursor sol by dissolving one or more metal salts into a liquid solution to a concentration of 0.01 to 1.0M;
(b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the HTL; (ii) forming the inorganic semiconductor nanocrystal layer by wet-chemical deposition; and (iii) forming the inorganic ETL by wet-chemical deposition including the steps:
(a) preparing a precursor sol by dispersing one or more nanoparticles in a solution; (b) depositing the precursor sol onto a surface; and
(c) heating the deposited precursor sol for a time and under conditions sufficient to form the ETL.
7. A method according to any one of claims 1 to 6, including the steps of forming the semiconductor nanocrystal layer on the HTL and subsequently forming the ETL on the semiconductor nanocrystal layer.
8. A method according to any one of claims 1 to 6, including the steps of forming the semiconductor nanocrystal layer on the ETL and subsequently forming the HTL on the semiconductor nanocrystal layer.
9. A method according to any one of claims 1 to 8 wherein the HTL precursor sol is formed by dissolving one or more metal salts into a liquid solution to a concentration of between 0.3 - 0.6M.
10. A method according to any one of claims 1 to 9 wherein the inorganic HTL is prepared at a heating temperature at 400 0C - 500 0C.
11. A method according to any one of claims 1 to 10, wherein the HTL exhibits high transparency over the visible wavelength region and exhibits an electrical resistivity of less than 100 Ωcm.
12. A method according to any one of claims 1 to 10 wherein the ETL precursor sol is formed by dissolving one or more metal salts into a liquid solution to a concentration of between 0.3 - 0.6M.
13. A method according to any one of claims 1 to 11 wherein the inorganic ETL is prepared at a heating temperature of 50 - 100 0C.
14. A method according to any one of claims 1 to 13, wherein the ETL exhibits an electrical resistivity of less than 100 Ωcm.
15. A method according to any one of claims 1 to 14, wherein the HTL is NiO based.
16. A method according to any one of claims 1 to 15, wherein the ETL is ZnO based.
17. A method according to any one of claims 2 to 6, wherein the depositing step comprises spin-coating.
18. A method according to any one of claims 1 to 17, wherein the inorganic semiconductor layer is formed by wet-chemical deposition which includes a heating step at a temperature range of 50-250°C, preferably 50-100 0C.
19. A method according to any one of claims 1 to 18, wherein the HTL and ETL are deposited from a solution wherein some condensation has already taken place.
20. A method according to any one of claims 2 to 6, wherein the precursor sol is heated prior to deposition.
21. A semiconductor device prepared by a method according to any one of claims 1 to 20.
22. A semiconductor device according to claim 21 which is a QD-LED.
23. A semiconductor device according to claim 21 or claim 22 which also further comprises two electrodes and a transparent substrate layer.
24. A semiconductor device comprising an inorganic electron transport layer (ETL), an inorganic semiconductor nanocrystal layer, and an NiO based hole transport layer (HTL).
25. A semiconductor device according to claim 24 wherein the ETL is ZnO based.
26. A semiconductor device according to claim 24 or claim 25, wherein the semiconductor nanocrystal layer is formed on the ETL and the HTL is formed on the semiconductor nanocrystal layer.
27. A semiconductor device according to any one of claims 24 to 26, wherein the HTL exhibits high transparency over the visible wavelength region and exhibits an electrical resistivity of less than 100 Ωcm.
28. A semiconductor device according to any one of claims 24 to 27, wherein the ETL exhibits an electrical resistivity of less than 100 Ωcm.
29. A semiconductor device according to any one of claims 24 to 28, which further comprises two electrodes and a transparent substrate layer.
30. A semiconductor device according to any one of claims 24 to 29, which is a QD- LED.
31. A semiconductor device substantially as hereinbefore described with reference to Figures 2 to 5.
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