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Definitions

• the present teachings relate to organic electroluminescent transistors with improved light emission characteristics. More specifically, the present electroluminescent transistors include a multilayer emissive ambipolar channel and by incorporating specific material(s) as one or more of the functional layers, the present electroluminescent transistors can achieve maximum brightness and efficiency simultaneously.
• OLETs Organic electroluminescent field effect transistors
• OLEDs Organic Light Emitting Diodes
• ambipolar OLETs have enhanced efficiency and luminosity, and also can afford the possibility of using low- cost production processes once they have been optimized.
• EP 1609195 discloses a three-layer organic light emitting transistor having an emissive ambipolar channel that includes at least one layer of an n-type semiconductor material, at least one layer of a p- type semiconductor material and at least one layer of an emissive material arranged between said layers of p-type and n-type semiconductor materials. Further details about the applications and the functional characteristics of these devices may be found in R. Capelli et al., "Organic light-emitting transistors with an efficiency that outperforms the equivalent light-emitting diodes," Nature Materials, vol. 9, pp. 496-503 (2010).
• the three-layer organic light-emitting transistor disclosed in Capelli et al. has a layer of an n-type semiconductor material composed of 5,5'-bis((5-perfluorohexyl)thiophen-2-yl)- 2,2'-bithiophene (DFH4T), a layer of a p-type semiconductor material composed of 5,5'- bis(3-hexyl-2-thienyl)-2,2'-bithiophene (DH4T), and a layer of an emissive material composed of tris(8-hydroxyquinolinato)aluminium:4-(dicyanomethylene)-2-methyl-6- (p-dimethylaminostyryl)-4H-pyran (Alq 3 :DCM).
• diacene-fused thienothiophenes specifically, [l]benzo-thieno[3,2- b][l]benzothiophenes (BTBTs) and dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophenes (DNTTs) have been shown to exhibit high mobility, air stability, and good reproducibility. See e.g., M.J.
• Kang et al "Two Isomeric Didecyl-dinaphtho[2,3- b:2',3'-f]thieno[3,2-b]thiophenes: Impact of Alkylation Positions on Packing Structures and Organic Field Effect Transistor Characteristics," Jpn. J. Appl. Phys., vol. 51 , pp. 1 1PD04 (2012); and H. Ebata et al, "Highly Soluble [l]Benzothieno[3,2- b]benzothiophene (BTBT) Derivatives for High-Performance, Solution-Processed Organic Field-Effect Transistors," J. Am. Chem. Soc, vol. 129, pp.
• C n -BTBT 2,7-dialkylderivatives of BTBT
• OFETs organic field-effect transistors
• EP 2402348 describes dialkyl- substituted DNTTs and related selenium analogs. OTFTs fabricated with the described compounds showed mobilities close to 4 cm 2 V "1 s "1 . No BTBT compounds are described.
• ambipolar OLET devices have an enhanced luminosity, though obtained at bias conditions where the efficiency of charge current conversion into light emission is very low (in the order of lx 10 "1 %). Conversely, the device efficiency can be usually maximized by modifying its bias conditions but with detrimental effects on the luminosity. These emission characteristics limit the possible application fields when high brightness and high efficiency are simultaneously needed such as, for example, in the fields of light emitting displays, Point of Care biomedical applications, and photon sources integrated on photonic chips. Further improvements in electroluminescence intensity (from the order of nanoWatt (nW) to micro Watt ⁇ W) with constant device geometry) also is desirable.
• An objective of the present teachings is to provide an organic electroluminescent transistor that can overcome the above mentioned drawbacks known in the art, in particular, to provide an organic electroluminescent transistor that can achieve maximum light emission efficiency and brightness simultaneously.
• an organic electroluminescent transistor comprises at least one dielectric layer, at least one control electrode, an assembly comprising an emissive ambipolar channel, at least one source electrode and at least one drain electrode, wherein:
• the dielectric layer is arranged between the control electrode and the assembly;
• the ambipolar channel comprises at least one layer of an n-type semiconductor material, at least one layer of a p-type semiconductor material and at least one layer of an emissive material arranged between the layers of p-type and n-type semiconductor materials;
• the p-type semiconductor material is suitable to transport holes across the ambipolar channel of the transistor and comprises a benzothieno-benzothiophene BTBT) compound having general formula (P-I)
• alkyl group and a C 6-14 aryl group.
• the n-type semiconductor material is a bis(p- fluoroalkyl)phenyl-substituted thieno[3,2-b]thiophene, non- limiting examples of which include 2,5-bis(4-(perfluorooctyl)phenyl)thieno[3,2-b]thiophene (NF2-6) and 2,5-bis(4- (trifluoromethyl)phenyl)thieno[3,2-b]thiophene (NF2-6-CF3).
• the emissive layer is selected from the group consisting of 4,4',4"-tris(carbazole-9-yl)triphenylamine :tris( 1 -phenylisoquinoline) iridium(III) (TCTA:Ir(piq) 3 ), 4,4'-bis(3,6-dineopentyl-9H-carbazole-9-yl)-l,'-biphenyl: tris(l-phenylisoquinoline)iridium(III) (NP4-CBP:Ir(piq) 3 ), 4,4'-bis(3,6-dineopentyl-9H- carbazole-9-yl)- 1 ,'-biphenyl:tris(2-phenylpyridine)iridium(III) (NP4-CBP:Ir(ppy)), 4,4'- bis(3,6-dineopentyl-9H-carbazole-9-yl)-l,'
• an organic electroluminescent transistor comprises at least one dielectric layer, at least one control electrode, an assembly comprising an emissive ambipolar channel, at least one source electrode and at least one drain electrode, wherein:
• the dielectric layer is arranged between the control electrode and the assembly;
• the ambipolar channel comprises at least one layer of an n-type semiconductor material, at least one layer of a p-type semiconductor material and at least one emissive layer of an emissive material arranged between the layers of the p-type and n-type semiconductor materials;
• the emissive layer comprises a blend material comprising a carbazole derivative as a host matrix compound and an iridium complex as a guest emitter.
• the organic electroluminescent transistor can include one or more additional layers selected from the group consisting of a hole- injection sublayer, an electron-injection sublayer, and a passivation layer.
• the source electrode is in contact with the layer of p-type semiconductor material and the drain electrode is in contact with the layer of n-type semiconductor material.
• an injection sublayer can be interposed between the source electrode and the layer of p-type or n-type semiconductor material and/or an injection sublayer is interposed between the drain electrode and the layer of p-type or n-type semiconductor material.
• Fig. 1 is a cross-sectional view of an organic light emitting transistor (OLET) according to an embodiment of the present teachings, which includes a substrate (1), a control electrode (2), a dielectric layer (3), an assembly comprising an emissive ambipolar channel that includes a layer of a first-type of semiconductor material (4), a layer of an emissive material (5), a layer of a second-type of semiconductor material (6), and an electron electrode and a hole electrode (7 and 7').
• OLET organic light emitting transistor
• Fig. 2 plots drain-source current I D s (left scale - black curves) and electroluminescence optical output power EL (right scale - gray curves) as a function of the drain-source voltage V DS at different values of the gate-source voltage V GS , as obtained from a first exemplary OLET having the architecture shown in Fig. 1 and incorporating a BTBT compound represented by formula (P-I) as the p-type semiconductor material.
• Fig. 5 plots drain-source current I D s (left scale - black curves) and electroluminescence optical output power EL (right scale - gray curves) as a function of the drain-source voltage V DS at different values of the gate-source voltage V GS , as obtained from a second exemplary OLET having the architecture shown in Fig. 1 and incorporating a different BTBT compound represented by formula (P-I) as the p-type semiconductor material.
• Fig. 8 plots drain-source current I D s (left scale - black curves) and electroluminescence output power EL (right scale - gray curves) as a function of the drain-source voltage V DS at different values of the gate-source voltage V GS , as obtained from a first comparative OLET having the architecture shown in Fig. 1 and
• DNTT comparative hole-transporting compound
• Fig. 9 plots drain-source current I D s (left scale - black curve)
• Fig. 1 1 plots drain-source current I D s (left scale - black curves) and electroluminescence output power EL (right scale - gray curves) as a function of the drain-source voltage V DS at different values of the gate-source voltage V GS , as obtained from a second comparative OLET having the architecture shown in Fig. 1 and incorporating a comparative hole-transporting compound previously reported in the literature that is not within formula (P-I) as the p-type semiconductor material.
• Fig. 14 plots drain-source current I D s (left scale - black curves) and electroluminescence optical output power EL (right scale - gray curves) as a function of the drain-source voltage V DS at different values of the gate-source voltage V GS , as obtained from a third exemplary OLET having the architecture shown in Fig. 1 and incorporating a blend material including an organic carbazole-based host matrix compound and an iridium complex guest emitter as the emissive layer.
• Fig. 17 depicts graphs of the drain-source current I D s (left scale - black curves) and of the electro-luminescence optical output power EL (right scale - gray curves) as a function of the drain-source voltage V DS at different values of the gate- source voltage V GS , for a third comparative electroluminescent transistor not according to the present teachings.
• the emissive layer is composed of a blend material including a metal complex host matrix compound and a platinum-based guest emitter.
• Fig. 1 shows the structure of an organic electroluminescent transistor (OLET) according to an embodiment of the present teachings.
• the OLET includes a substrate 1 that acts as a supporting layer, over which there is an electrode 2 that acts as the control (or gate) electrode and that may be a transparent electrode, and a layer of dielectric material 3, over which there is a light- emitting assembly.
• the light-emitting assembly generally includes a charge carrier transport layer of a first type 4, a layer 5 of emissive material, and a charge carrier transport layer of a second type 6.
• the charge carrier transport layer of the first type 4 can be a hole transport layer made of a p-type semiconductor material and the charge carrier transport layer of the second type 6 can be an electron transport layer made of an n-type semiconductor material, although an inverted assembly (with layer 4 being an electron transport layer made of an n-type semiconductor material and layer 6 being a hole transport layer made of a p-type semiconductor material) also can be used.
• Hole and electron electrodes 7 and 7 are realized so as to inject charge carriers into the light-emitting assembly. In the shown embodiment, the hole and electron electrodes are directly in contact with the charge carrier transport layer of the second type 6.
• an injection sublayer i.e., a hole- injection sublayer
• an injection sublayer i.e., an electron-injection sublayer
• an injection sublayer can be interposed between the electron electrode and the layer 6.
• the hole electrode and the electron electrode can function, respectively, as the source electrode and the drain electrode (or vice versa) depending on the polarity of the gate voltage.
• the source electrode is typically grounded (0 V)
• the gate voltage is - 100V and the drain voltage is -80V
• the source electrode is the hole electrode (negatively biased) and the drain electrode is the electron electrode (positively biased).
• the gate voltage is + 100V
• the source electrode is the electron electrode and the drain electrode is the hole electrode.
• An OLET typically is operated by applying a first appropriate bias voltage to the gate electrode, and injecting electrons from the electron electrode and holes from the hole electrode, while maintaining a second bias voltage between the latter two electrodes.
• the first and second bias voltages can be continuous voltages. In other embodiments, the first and second bias voltages can be pulsed voltages.
• an OLET can have a top-gate architecture.
• the hole and electron electrodes and/or the control electrode can have alternative arrangements as described in International Publication No. WO 2014/035841.
• the hole and electron electrodes can be in contact with different layers of the light-emitting assembly.
• the hole electrode can be in contact with the layer of p-type semiconductor material, while the electron electrode can be in contact with the layer of n-type semiconductor material.
• WO 2013/018002 WO 2013/017999, WO 2014/035842, and WO 2013/018000
• additional control electrode(s) and/or additional layer(s) of dielectric material, emissive material, and/or charge carrier transport materials can be incorporated into the OLET.
• a passivation layer can be present covering the top surface of the emissive ambipolar channel.
• the inventors have found that the foregoing organic electroluminescent transistors such as, but not limited to, those configured according to the embodiment shown in Fig. 1 , can have enhanced light emission if the p-type semiconductor material includes a benzothieno-benzothiophene (BTBT) compound of the formula (P-I):
• BBT benzothieno-benzothiophene
• R a and R b are independently selected from the group consisting of H, a Ci_is alkyl group, and a C 6 -i4 aryl group.
• the benzothieno- nzothiophene compound can have the formula:
• R a and R b are identical Ci_is alkyl groups, preferably identical C 3 _i 2 alkyl groups, and most preferably identical linear C3-12 alkyl groups.
• Specific non-limiting examples include 2,7-dioctyl[l]benzo-thieno[3,2-b][l] benzothiophene (C8-BTBT) and 2,7-dipentyl[l]benzo-thieno[3,2-b][l] benzothiophene (C5-BTBT).
• benzothieno-benzothiophene compound can have the formu
• each R can be a phenyl group.
• DNTTs dinaphtho[2,3-b:2',3'- f]thieno[3,2-b]thiophenes
• the emissive material comprises a blend of an organic carbazole-based host matrix compound and an iridium complex guest emitter.
• the organic carbazole-based host matrix compound can be represented by either formula (H-l) (TCTA), formula (H-2) (NP4-CBP), or formula (H-3) (CBP or 4,4'-bis(N-carbazolyl)-l,l'-biphenyl) and a guest emitter represented by formula (G-1) (Flrpic), formula (G-2) (Ir(ppy)), or formula (G-3) (Ir(piq) 3 ) as provided below.
• the layer of emissive material can include between 5% and 22% of its total weight of the guest emitter.
• the emissive material can include a blend of the arylamine matrix compound of (H-1) and the blue emitter of formula (G-1):
• the emissive material can include a blend of the arylamine matrix compound of formula (H-1) and the green emitter of formula (G-2):
• the emissive material can include a blend of the arylamine matrix compound of formula (H-1) and the red emitter of formula (G-3):
• the emissive material can be selected from various single- component host-emitting materials and blend materials including a host matrix compound and a guest fluorescent or phosphorescent emitter known in the art. Suitable organic electroluminescent light-emitting materials include those having been used in OLED applications.
• an alternative emissive material can be a blend of tris(8-hydroxyquinolinato)aluminium (Alq 3 ) as the host matrix compound and 4- (dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) as the guest emitter.
• some exemplary host-emitting materials include phosphorescent host- emitting compounds based on carbazole derivatives, fluorene derivatives, or 9- naphthylanthracene derivatives, and fluorescent host-emitting compounds based on organometallic chelates such as tris(8-quinolinol) aluminum complexes.
• Some exemplary host materials include polymers such as poly(/?-phenylene vinylene), poly(alkyphenylphenylvinylene), poly(alkyphenylphenylvinylene-co- alkoxyphenylenevinylene), polyfluorene, poly(n-vinylcarbazole), and copolymers thereof.
• Various carbazole compounds, triphenylamine compounds, including hybrids with oxadiazole or benzimidazole also have been used as host materials.
• Some exemplary guest emitters include fluorescent dyes such as various perylene derivatives, anthracene derivatives, rubrene derivatives, carbazole derivatives, fluorene derivatives, and quinacridone derivatives, and phosphorescent emitters such as various transition metal complexes including Ir, Os, or Pt. Tests carried out by the applicant showed that light emission figures are further enhanced when the emissive layer is selected among TCTA:Ir(piq)3, NP4- CBP:Ir(piq) 3 , NP4-CBP:Ir(ppy), NP4-CBP:FIrpic.
• the layer of emissive material contains a concentration of a doping material (e.g. one of the above described transition metal complexes) that is comprised between 5 and 22% of the total weight of the emissive layer.
• the n-type semiconductor material can include a bis(p-fluoroalkyl)phenyl-substituted oligomeric thiophene compound, where the oligomeric thiophene compound can have 2, 3, 4, 5 or 6 thiophene moieties, optionally where two or more of the thiophene moieties can be fused.
• the bis(p- fluoroalkyl)phenyl-substituted oligomeric thiophene compound can be selected from the group consisting of a dithiophene, a quaterthiophene, and a thienothiophene,
• the inventors have found that the foregoing organic electroluminescent transistors can have enhanced emissive properties if the n-type semiconductor material includes an electron-trans orting compound represented by formula (N-l):
• X is selected from the group consisting of S, O, and Se;
• Ar and Ar' at each occurrence, independently are identical or different monocyclic aryl or heteroaryl groups
• R 1 and R 2 independently are identical or different electron-withdrawing groups selected from the group consisting of -CN, R 3 , -C(0)R 4 , and -C(0)OR 4 ; wherein R 3 is an alkyl, alkenyl, or alkynyl group substituted with one or more F or CN groups, and R 4 is an alkyl, alkenyl, or alkynyl group optionally substituted with one or more F or CN groups; and
• n and m' independently are 1 or 2.
• R 1 and R 2 can be R 3 which is selected from the group consisting of (i) a Ci_ 2 o alkyl group substituted with one or more F or CN groups having the general formula C x F y H 2x+ i_ y or C x CN y H 2x+ i_ y , provided that x is an integer ranging between 1 and 20, y is an integer ranging between 1 and 41 , and y ⁇ 2x+l ; (ii) a C 2 _ 2 o alkenyl group substituted with one or more F or CN groups having the general formula C x F y H 2x _i_ y or C x CN y H 2x _i_ y , provided that x is an integer ranging between 2 and 20, y is an integer ranging between 1 and 39, and y ⁇ 2x-l ; (iii) a C 2 _ 2 o alkynyl group substituted with one or more F
• R 1 and R 2 can be a Ci_ 2 o alkyl group substituted with one or more F groups having the general formula C x F y H 2x+ i_ y , provided that x is an integer ranging between 1 and 20, y is an integer ranging between 1 and 41 , and y ⁇ 2x+l .
• R 1 and R 2 can be a CMS perfluoroalkyl group having the general formula C n F 2n+ i, provided that n is an integer ranging between 1 and 20.
• R 1 and R 2 can be -C(0)R 4 or -C(0)OR 4 , where R 4 is selected from the group consisting of (i) H, (ii) a Ci_is alkyl group optionally substituted with one or more F or CN groups having the general formula C x F y H 2x+ i- y or C x CN y H 2x+ i_ y , provided that x is an integer ranging between 1 and 20, y is an integer ranging between 0 and 41 , and y ⁇ 2x+l (ii) a C 2 _is alkenyl group optionally substituted with one or more F or CN groups having the general formula C x F y H 2x _i_ y or C x CN y H 2x _i_ y , provided that x is an integer ranging between 2 and 20, y is an integer ranging between 0 and 39, and y ⁇ 2x-l ; and (ii)
• the electron-transporting compound can be represented by formula N-2):
• Ar, Ar', R 1 , R 2 , m and m' are as defined herein.
• the electron-transporting compound can be represented by formula (N-3 :
• n is an integer ranging from 1 to 12 (inclusive), preferably, from 4 to 12 (inclusive), and wherein Ar, Ar', m and m' are as defined herein.
• Ar and Ar' at each occurrence, independently can be selected from the group consisting of a phenyl group, a thienyl group, a thiazolyl group, an isothiazolyl group, a thiadiazolyl group, a furyl group, an oxazolyl group, an isoxazolyl group, an oxadiazolyl group, a pyrrolyl group, a triazolyl group, a tetrazolyl group, a pyrazolyl group, an imidazolyl group, a pyridyl group, a pyrimidyl group, a pyridazinyl group, and a pyrazinyl group.
• the electron-transporting compound can be represented by formula N-4):
• the electron-transporting compound can be 2,5- bis(4-(perfluorooctyl) henyl)thieno[3,2-b]thiophene (N-F2-6):
• the electron-transporting compound can be 2,5-bis(4-(trifluorometh l)phenyl)thieno[3,2-b]thiophene (NF2-6-CF3):
• the dielectric layer can be an electrically insulating material selected from the group consisting of an inorganic oxide or nitride, a molecular dielectric, a polymeric dielectric, and combination thereof.
• the dielectric layer is a metal oxide or nitride
• such dielectric material can be selected from the group consisting of SiC"2, S13N4, AI2O3, ZrO x , Al-doped ZrO x , and HfO x .
• the dielectric layer is a molecular dielectric
• such dielectric can be a self-assembled nanodielectric.
• the dielectric layer is a polymeric dielectric
• such dielectric material can be selected from the group consisting of polyolefms, polyacrylates, polyimides, polyesters, and fluoropolymers. Hybrid organic/inorganic materials also may be used.
• the dielectric layer comprises an organic dielectric, particularly, a polymeric dielectric.
• organic electroluminescent transistors including at least one dielectric layer, at least one control electrode, an assembly comprising an emissive ambipolar channel, at least one source electrode and at least one drain electrode, wherein:
• the dielectric layer is arranged between the control electrode and the assembly;
• the ambipolar channel comprises at least one layer of an n-type semiconductor material, at least one layer of a p-type semiconductor material and at least one emissive layer of an emissive material arranged between the layers of the p-type and n-type semiconductor materials;
• the emissive layer is composed of a blend material that includes an organic carbazole derivative as the host matrix compound and an iridium complex as the guest emitter.
• the organic carbazole-based host matrix compound can be represented by either formula (H-l) (TCTA), formula (H-2) (NP4- CBP), or formula (H-3) (CBP or 4,4'-bis(N-carbazolyl)-l,l'-biphenyl) and the guest emitter can be represented by formula (G-l) (FIrpic), formula (G-2) (Ir(ppy)), or formula (G-3) (Ir(piq) 3 ).
• a metal complex host matrix compound such as Alq 3
• OLETs can be fabricated using processes known in the art.
• organic layers e.g., the layer of emissive material, the layers of p-type and n-type semiconductor materials, and the organic dielectric layer of certain embodiments
• vapor-phase processes such as chemical vapor deposition or physical vapor deposition, as well as solution-phase processes such as printing (e.g., flexo printing, litho printing, gravure printing, ink-jetting, pad printing, and so forth), drop casting, slot coating, dip coating, doctor blading, roll coating, or spin-coating.
• the hole/electron and gate electrodes can be formed using conventional processing techniques.
• any of the electrical contacts can be deposited through a mask, or can be deposited then etched or lifted off (photolithography).
• Suitable deposition techniques include electrodeposition, vaporization, sputtering, electroplating, coating, laser ablation and offset printing, from the same or different metals or metal alloys such as copper, aluminum, gold, silver, molybdenum, platinum, palladium, copper, titanium, chromium, and/or nickel, a transparent conducting oxide such as tin-doped indium oxide (ITO), or an electrically conductive polymer such as polyethylenethioxythiophene (PEDOT).
• ITO tin-doped indium oxide
• PEDOT polyethylenethioxythiophene
• Charge carrier injection can be facilitated by the use of a material for the injection electrode (hole electrode or electron electrode) that has a low barrier against injection of a charge carrier type into the hole transport sublayer and the electron transport sublayer, respectively.
• the hole electrode can comprise at least one material selected from the group consisting of Au, indium tin oxide, Cr, Cu, Fe, Ag, poly(3,4-ethylenedioxthiophene) combined with poly(styrenesulfonate) (PEDOT:PSS), and a perovskite manganite (Rei_ x A x Mn03).
• the hole electrode and the electron electrode can be made of conductors with different work functions to favor both hole and electron injection.
• the hole and electron injection sublayers can be prepared by self- assembly of thiolates, phosphonates, or aliphatic or aromatic carboxylates; by thermal evaporation of various charge transfer complexes and other heteroaromatic or organometallic complexes; or by thermal evaporation or sputtering of various metal oxides, fluorides, or carbonates.
• the hole injection sublayer and the electron injection sublayer can be made of materials that provide a staircase of electronic levels between the energy level of the hole electrode and the electron electrode, and the energy level required for injection into the hole transport sublayer and the electron transport sublayer, respectively.
• OLETs can be fabricated on various substrates including plastic, flexible substrates that have a low temperature resistance.
• flexible substrates include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polycarbonate; polyolefms such as polypropylene, polyvinyl chloride, and polystyrene; polyphenylene sulfides such as polyphenylene sulfide; polyamides; aromatic polyamides; polyether ketones; polyimides; acrylic resins; polymethylmethacrylate, and blends and/or copolymers thereof.
• the substrate can be a rigid transparent substrate such as glass, quartz and VYCOR®.
• Substrate-gate materials commonly used in thin-film transistors also can be used. Examples include doped silicon wafer, tin-doped indium oxide (ITO) on glass, tin-doped indium oxide on polyimide or mylar film, aluminum or other metals alone or coated on a polymer such as polyethylene terephthalate, a doped polythiophene, and the like.
• ITO tin-doped indium oxide
• polyimide or mylar film aluminum or other metals alone or coated on a polymer such as polyethylene terephthalate, a doped polythiophene, and the like.
• the thicknesses of the various layers may be adapted in order to optimize performances and scaling down of the electroluminescent transistor of this disclosure.
• the thickness of the layer of p-type semiconductor material comprised between 5 and 50 nm, preferably between 15 and 45 nm
• the thickness of the layer of n-type semiconductor material may be comprised between 30 nm and 60 nm
• the thickness of the layer of emissive material may be comprised between 30 nm and 60 nm.
• a plurality of OLETs can be arranged in a matrix to provide a display device.
• the display device can include optional driving and switching elements, compensating transistor elements, capacitors, and/or light-emitting diodes.
• optional driving and switching elements and compensating transistor elements can be organic field-effect transistors.
• NP4-CBP 4,4'-bis(3,6-dineopentyl-9H-carbazole-9-yl)-l,'-biphenyl
• PtOEP 2,3,7,8,12,13,17, 18-octaethylporphyrin-22,24-diide
• an organic ambipolar light-emitting transistor according to the present teachings was fabricated on a glass substrate (first layer 1), onto which a transparent control electrode 2 made of ITO (indium tin oxide) was provided.
• a 450 nm-thick dielectric layer 3 composed of poly(methyl)
• PMMA methacrylate methacrylate
• a hole transport layer 4 composed of a p-type semiconductor material deposited over the dielectric layer 3, specifically, a 15 nm-thick film made of C8-BTBT sublimated at a rate of 0.1 A/s, while the substrate was maintained at room temperature;
• an emissive layer 5 in contact with the hole transport layer 4 specifically, a 60 nm-thick recombination layer composed of a host-guest system (with a guest emitter concentration of 20%).
• TCTA was used as the host matrix and it was sublimated at a rate of 1 A/s, while the substrate was maintained at room temperature.
• Ir(piq) 3 was used as the guest emitter and it was sublimated at a rate of 0.25 A/s, while the substrate was maintained at room temperature; and
• an electron transport layer 6 in contact with the emissive layer 5 specifically, a 45 nm-thick film of N-F2-6 sublimated at a rate of 0.1 A/s, while the substrate was maintained at room temperature.
• the metal source and drain electrodes 7 and 7' made of silver (Ag), were deposited in vacuum (10 ⁇ 6 mbar) and each has a thickness of 70 nm.
• the device channel length (L) and channel width (W) are 70 ⁇ and 12 mm, respectively.
• p-type threshold voltage -40.1 V
• n-type threshold voltage 38.4 V
• n-type mobility 3.6x 10 "3 cm 2 /Vs.
• FIG. 2 illustrates variations of the drain-source current (I D s) (left scale - black curves) and the electroluminescence optical output power (EL) (right scale - gray curves) as a function of the drain-source voltage (V D S) at different gate-source voltages (VGS), while the source contact was grounded.
• I D s drain-source current
• EL electroluminescence optical output power
• I DS drain-source current
• EL electroluminescence optical output power
• the tested OLET which has an organic emissive ambipolar channel that includes a hole transport layer composed of a BTBT compound (in this case, C8-BTBT) unexpectedly achieved maximum brightness (EL ⁇ 45 ⁇ W) and efficiency (EQE ⁇ 2.25%) simultaneously.
• a BTBT compound in this case, C8-BTBT
• a second OLET was fabricated in the same manner and using the same materials as the OLET described in Example 1 , except that a different BTBT compound was used in the hole transport layer 4.
• the hole transport layer 4 was composed of a 15 nm-thick film made of C5-BTBT instead of C8-BTBT.
• p-type threshold voltage -54.5 V
• n-type threshold voltage 25.9 V
• n-type mobility 4.2x 10 "3 cm 2 /Vs.
• FIG. 5 illustrates variations of the drain-source current (I D s) (left scale - black curves) and the electroluminescence optical output power (EL) (right scale - gray curves) as a function of the drain-source voltage (V DS ) at different gate-source voltage (V GS ), while the source contact was grounded.
• I D s drain-source current
• EL electroluminescence optical output power
• the tested OLET which has an organic emissive ambipolar channel that includes a hole transport layer composed of a BTBT compound (in this case, C5-BTBT) unexpectedly achieved maximum brightness (EL > 50 ⁇ W) and efficiency (EQE > 2.5%) simultaneously.
• a BTBT compound in this case, C5-BTBT
• the comparative device tested in this example incorporated a DNTT compound as the p-type semiconductor material in the hole transport layer 4.
• DNTT compounds which have naphthalene, i.e., 2 benzene rings, fused to each side of the thienothiophene center
• BTBT compounds which have only 1 benzene ring fused to each side of the thienothiophene center
• the comparative OLET was fabricated in the same manner and using the same materials as the OLET described in Example 1 , except that the hole transport layer 4 was composed of a 15 nm-thick film made of DNTT instead of C8- BTBT.
• FIG. 8 illustrates variations of the drain-source current (I D s) (left scale - black curves) and the electroluminescence optical output power (EL) (right scale - gray curves) as a function of the drain-source voltage (V D S) at different gate-source voltage (VGS), while the source contact was grounded.
• I D s drain-source current
• EL electroluminescence optical output power
• I DS drain-source current
• EL electroluminescence optical output power
• Fig. 10 shows graphs of the external quantum efficiency (EQE, left scale - black curve) and of the electroluminescence optical output power EL (right scale - gray curves) as a function of the gate-source voltage V GS while the drain contact was maintained at a constant bias voltage of -100V and the source contact was grounded
• the electroluminescence achieved by the DNTT-based OLET was less than 50% of the electroluminescence achieved by the BTBT-based OLETs (which was EL ⁇ 45 ⁇ , and EL > 50 ⁇ , respectively).
• the comparative OLET device tested in this example incorporated the p-type semiconductor material (DH4T), the n-type semiconductor material (DFH4T, a bis(fluoroalkyl-substituted) oligothiophene), and the emissive material (Alq 3 :DCM) used in the organic light-emitting transistor reported in R.
• DH4T p-type semiconductor material
• DVF4T n-type semiconductor material
• Alq 3 :DCM emissive material
• a comparative OLET was fabricated on a glass substrate (first layer 1), onto which a transparent control electrode 2 made of ITO (indium tin oxide) was provided.
• a 450 nm-thick dielectric layer 3 composed of poly(methyl methacrylate) (PMMA) was fabricated on the ITO electrode by spin-coating and cured in vacuum at 90°C.
• An organic emissive ambipolar channel was formed on the dielectric layer by sublimation in vacuum (10 ⁇ 7 mbar) and includes the following layers:
• an emissive layer 5 in contact with the hole transport layer 4 specifically, a 60 nm-thick recombination layer composed of a host-guest system (with a guest emitter concentration of 20%).
• Alq 3 was used as the host matrix and it was sublimated at a rate of 1 A/s, while the substrate was maintained at room temperature.
• DCM was used as the guest emitter and it was sublimated at a rate of 0.25 A/s, while the substrate was maintained at room temperature; and
• the metal source and drain electrodes 7 and 7' made of silver (Ag), were deposited in vacuum (10 ⁇ 6 mbar) and each has a thickness of 70 nm.
• the device channel length (L) and channel width (W) are 70 ⁇ and 12 mm, respectively.
• p-type threshold voltage -60 V
• n-type threshold voltage 23.7 V
• n-type mobility 3.6x 10 "3 cm 2 /Vs.
• FIG. 11 illustrates variations of the drain-source current (I D s) (left scale - black curves) and the electroluminescence optical output power (EL) (right scale - gray curves) as a function of the drain-source voltage (V DS ) at different gate-source voltage (V GS ), while the source contact was grounded.
• I D s drain-source current
• EL electroluminescence optical output power
• V GS gate-source voltage
• Another aspect of the present teachings is directed to the use of an emissive material in a trilayer OLET device, where the emissive material is a blend including an organic arylamine matrix compound (H-l) or (H-2) and an iridium-based emitter selected from (G-l), (G-2), and (G-3).
• the emissive material is a blend including an organic arylamine matrix compound (H-l) or (H-2) and an iridium-based emitter selected from (G-l), (G-2), and (G-3).
• an organic ambipolar light-emitting transistor (OLET) according to the present teachings was fabricated on a glass substrate (first layer 1), onto which a transparent control electrode 2 made of ITO (indium tin oxide) was provided.
• An organic emissive ambipolar channel was formed on the dielectric layer by sublimation in vacuum (10 ⁇ 7 mbar) and includes the following layers:
• a hole transport layer 4 composed of a p-type semiconductor material deposited over the dielectric layer 3, specifically, a 45 nm-thick film made of DH4T sublimated at a rate of 0.1 A/s, while the substrate was maintained at room temperature;
• an emissive layer 5 in contact with the hole transport layer 4 specifically, a 60 nm-thick recombination layer composed of a host-guest system (with a guest emitter concentration of 20%).
• TCTA was used as the host matrix and it was sublimated at a rate of 1 A/s, while the substrate was maintained at room temperature.
• Ir(piq) 3 was used as the guest emitter and it was sublimated at a rate of 0.25 A/s, while the substrate was maintained at room temperature; and
• an electron transport layer 6 in contact with the emissive layer 5 specifically, a 45 nm-thick film of N-F4-1 sublimated at a rate of 0.1 A/s, while the substrate was maintained at room temperature.
• the metal source and drain electrodes 7 and 7' made of silver (Ag), were deposited in vacuum (10 ⁇ 6 mbar) and each has a thickness of 70 nm.
• the device channel length (L) and channel width (W) are 70 ⁇ and 12 mm, respectively.
• p-type threshold voltage -49 V
• p-type mobility 1.3 x 10 "1 cm 2 /V s;
• n-type threshold voltage null
• n-type mobility null.
• FIG. 14 illustrates variations of the drain-source current (I D s) (left scale - black curves) and the electroluminescence optical output power (EL) (right scale - gray curves) as a function of the drain-source voltage (V DS ) at different gate-source voltages (V GS ), while the source contact was grounded.
• I D s drain-source current
• EL electroluminescence optical output power
• V GS gate-source voltage
• Fig. 16 shows graphs of the external quantum efficiency (EQE, left scale - black curve) and of the electroluminescence optical output power EL (right scale - gray curves) as a function of the gate-source voltage V GS while the drain contact was maintained at a constant bias voltage of -100V and the source contact was grounded
• the tested OLET which has an emissive layer within the trilayer channel that includes a blend material composed of TCTA:Ir(piq) 3 , i.e., the carbazole derivative TCTA as the host matrix compound and the iridium complex Ir(piq) 3 as the guest emitter, unexpectedly achieved maximum brightness (EL ⁇ 2 ⁇ W) and efficiency (EQE > 0.4%) simultaneously.
• a comparative OLET device was fabricated in the same manner and using the same materials as the OLET described in Example 5, except that a different blend material was used in the emissive layer 5.
• the emissive layer 5 was a blend material composed of Alq 3 :PtOEP, that is, both the host matrix and the guest emitter are metal complexes, and the guest emitter is a platinum-based complex instead of an iridium-based complex.
• p-type threshold voltage -55.2 V
• n-type threshold voltage null
• n-type mobility null.
• FIG. 17 illustrates variations of the drain-source current (I D s) (left scale - black curves) and the electroluminescence optical output power (EL) (right scale - gray curves) as a function of the drain-source voltage (V DS ) at different gate-source voltage (V GS ), while the source contact was grounded.
• I D s drain-source current
• EL electroluminescence optical output power
• Table 2 summarizes the materials used in each layer within the trilayer ambipolar channel of the OLET devices described in Examples 1-6, together with their respective maximum EL and EQE values.

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