KR102018291B1 - All in one single molecule and single molecular organic solar cells comprising the same - Google Patents

Abstract

The present invention relates to an all-in-one single molecule and a single molecule organic solar cell including the same. Specifically, an all-in-one single molecule having an electron donor and an electron acceptor in one structure, and an organic solar cell including the same are provided.

Description

All-in-one monomolecule and monomolecular organic solar cell comprising same {ALL IN ONE SINGLE MOLECULE AND SINGLE MOLECULAR ORGANIC SOLAR CELLS COMPRISING THE SAME}

The present invention relates to an all-in-one single molecule and a single molecule organic solar cell including the same. Specifically, an all-in-one single molecule having an electron donor and an electron acceptor in one structure, and an organic solar cell including the same are provided.

Organic solar cells (ORGANIC SOLAR CELLS, OSCs) are one of the promising candidates for manufacturing large area and thin film solar panels because of solution processability, light weight and flexibility. Excellent power conversion efficiencies (PCEs) have been reported through gradual advances in photovoltaic material synthesis and device fabrication methods such as new device configurations, morphology optimization, and interface processing. Ternary (or multiple) blend systems and stacked (or multijunction) device structures are used mainly to produce organic solar cells with good performance, which is becoming increasingly complex in device structure and providing photoactive layers in one device. This means that the number of constituent photoactive materials is increased. In addition, novel non-fullerene-based acceptor structures have been introduced to replace fullerene derivative acceptors (S. Li, L. Ye, W. Zhao, S. Zhang, S. Mukherjee, H. Ade, J. Hou, Adv Mater 2016, 28, 9423; Y. Lin, J. Wang, ZG Zhang, H. Bai, Y. Li, D. Zhu, X. Zhan, Adv Mater 2015, 27, 1170.). In other words, as the power conversion efficiencies (PCEs) of OSCs increase, the fabrication of photoactive layer films becomes more complex and the variables considered such as batch-to-batch variation and morphology optimization are increasing.

Korean Patent Publication No. 2015-0048636 discloses a single molecule and an organic solar cell including the same. In the above patent, the electron donor material is composed of the single molecule, and the electron acceptor material is selected from PCBM and the like and mixed to form a photoactive layer. However, the patent discloses only the configuration of mixing the electron donor material and the electron acceptor material.

Some papers disclose “organic dyad compound” photovoltaic devices (S. Izawa, K. Hashimoto, K. Tajima, Phys Chem Chem Phys 2012, 14, 16138; S. Izawa, K. Hashimoto, K. Tajima, Chem Commun (Camb) 2011, 47, 6365; T. Nishizawa, HK Lim, K. Tajima, K. Hashimoto, Chem Commun (Camb) 2009, 2469; T. Nishizawa, K. Tajima, K. Hashimoto , J. Mater. Chem. 2007, 17, 2440; K. Narayanaswamy, A. Venkateswararao, P. Nagarjuna, S. Bishnoi, V. Gupta, S. Chand, SP Singh, Angew Chem Int Ed Engl 2016, 55, 12334 However, these papers did not achieve reasonable PCEs and external quantum efficiencies (EQEs) of the device, and also did not fully investigate the advantages compared to a two-hop blend device.

MEANS TO SOLVE THE PROBLEM In order to solve the above-mentioned problem of the prior art, the present inventors all-in-one single molecule which has an electron donor and an electron acceptor in one structure, and the organic solar system including the same To provide a battery.

The above object is an organic single molecule having a [ADA] structure, wherein A is a PCBM-derived compound, and D is benzo [1,2- b : 4,5- b ' ] dithiophene (benzo [1,2]. b : 4,5- b ' ] dithiophene (BDT) as a central unit, wherein said organic monomolecule is achieved by an organic monomolecule, which is a compound of formula

[Formula 1]

Preferably, A is an electron acceptor, and D may be an electron donor.

Also preferably, the molar ratio of D: A may be 1: 2.

According to one embodiment of the invention, the first electrode formed on the substrate, the second electrode formed to face the first electrode, at least one organic layer formed between the first electrode and the second electrode and including a photoactive layer An organic solar cell comprising the above, wherein the photoactive layer provides an organic solar cell including an organic single molecule having a [ADA] structure: A is a compound derived from PCBM, and D is benzo [1,2- b : 4,5- b ' ] dithiophene (benzo [1,2- b : 4,5- b' ] dithiophene, BDT) is a compound containing as a central unit, the organic single molecule is a compound of formula (1).

[Formula 1]

.

.

Preferably, the organic material layer may include a hole transport layer, a hole injection layer, or a layer for simultaneously performing hole transport and hole injection.

Also preferably, the organic material layer may include an electron injection layer, an electron transport layer, or a layer for simultaneously performing electron injection and electron transport.

According to an embodiment of the present invention, the organic solar cell may include a first electrode, a hole transport layer, a photoactive layer, an electron transport layer, and a second electrode. In this case, the material of the hole transport layer is PEDOT: PSS (Poly (3,4-ethylenediocythiophene doped with poly (styrenesulfonic acid), molybdenum oxide (MoO _x ), vanadium oxide (V ₂ O ₅ ), nickel oxide (NiO), And tungsten oxide (WO _x ), and the material of the electron transport layer may include zinc oxide (ZnO), titanium oxide (TiO _x ), LiF, and cesium carbonate (Cs ₂ CO ₃ ). It may be one selected from the group consisting of.

Preferably, the first electrode may include one selected from the group consisting of chromium, copper, zinc, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO).

Also preferably, the second electrode may be one selected from the group consisting of aluminum, silver, magnesium, copper, tin, lithium, titanium, potassium, magnesium, calcium, sodium, and lead.

The monomolecular organic solar cell according to the present invention can be manufactured simply and at low cost without complicated processing, and has a power conversion efficiency (PCE) of up to 2.44% and an external quantum efficiency (EQE) of up to 46%.

1 illustrates a material forming the all-in-one monomolecule according to the present invention, structural formula (a), and energy levels (b) of the respective materials.
FIG. 2 shows (a) JV characteristics, (b) EQE spectrum, and (c) J _sc of an all-in-one organic solar cell and a BDTRH-OH: PCBM (blend) organic solar cell according to the present invention. Light intensity dependence, (d) the light intensity dependence of V _oc .
3 shows (a) JV characteristics and (b) photocurrent measurements in the dark of a BDTRh-OH: PCBM (blend) device and a BDTRh-PCBM (all-in-one) device.
Figure 4 shows the transport characteristics of (a) BDTRh-OH FET, (b) Ambipolar transport characteristics of BDTRh-OH: PCBM (blend) FET and BDTRh-PCBM (all-in-one) FET. (c) the bipolar output characteristics of the blend FET and (d) the bipolar output characteristics of the all-in-one FET. In (c) and (d), V _gs increased with the steps of red, orange, yellow, green, cyan, blue and purple.
FIG. 5 shows JV characteristics of (a) hole only devices and (b) electron only devices based on BDTRh-OH: PCBM (blend) film and BDTRh-PCBM (all-in-one) film.
6 is a Tauc plot of (a) an all-in-one membrane and a BDTRh-OH: PCBM (blend) membrane according to the present invention, and (b) an all-in-one device according to the present invention. And EQE spectra in the CT region between the BDTRh-OH: PCBM (blend) device. The solid curve is according to equation (1).
FIG. 7 shows (a) absorption spectrum and (b) photoluminescence of BDTRh-OH, BDTRh-OH: PCBM blend and BDTRh-PCBM.
8 shows (a) transient absorption spectra (TAS) of neat BDTRh-OH membranes at 2.17 eV excitation and (b) of neat BDTRh-OH membranes at 1.24 eV, 1.12 eV and 1.03 eV EX and SE. The kinetics are shown.
Figure 9 shows (a) BDTRh-OH: PCBM and (b) transient absorption spectra (TAS) of BDTRh-PCBM at different time delays, (c) BDTRh-OH: PCBM, and (d) Exciton and Polaron kinetics of BDTRh-PCBM.
FIG. 10 is the intensity detected at 1.4 eV (polaron peak) and 1.03 eV (exciton peak) for BDTRh-OH: PCBM blends (a, c) and BDTRh-PCBM (b, d) and with excitation energy at 2.17 eV. It shows the dependency TAS profile.
FIG. 11 shows the surface morphology of the blend film and the all-in-one film with tapping atomic force microscopy (AFM) images, where a and b are AFM shape images and c and d are phase images. a and c are BDTRh-OH: PCBM (Blend) films, and b and d are BDTRh-OH: PCBM (Blend) films.
12 is a 2D GIWAXS image of (a) BDTRh-OH (core) film, (b) BDTRh-OH: PCBM (Blend) film and (c) BDTRh-PCBM (All-in-one) film, (d) In plane and (e) out-of-plane.

The present invention relates to an all-in-one single molecule and a single molecule organic solar cell including the same.

According to a preferred embodiment of the present invention, the all-in-one monomolecule of the present invention has a [A-D-A] structure and is a compound of the following structural formula (1).

[Formula 1]

In the above, A is a fullerene derivative PCBM ([6,6] -phenyl-C61-butyric acid-methylester), and D is benzo [1,2- b : 4,5- b ' ] dithiophene (benzo [1, 2- b : 4,5- b ' ] dithiophene (BDT) as a BDTRH containing as a central unit, has the following structural formula (2).

[Formula 2]

Figure 1 shows the structural formula (a) and the energy level of each material (b) and the material forming the all-in-one monomolecule according to the present invention.

Referring to Figure 1 (a) and the structural formula 1, the all-in-one single molecule (hereinafter referred to as 'BDTRh-PCBM') according to the present invention is composed of a BDTRh-OH-derived electron donor core and PCBM-derived two electron acceptor wings. Comparing this BDTRh-PCBM with BDTRh-OH, it has a deeper highest occupied molecular orbital (HOMO) energy level (-5.15 eV → -5.32 eV), and the lowest unoccupied molecular orbital (LUMO) energy level is both Same at -3.55 eV (FIG. 1 (b)). As a result, the bandgap energy of BDTRh-PCBM is somewhat larger than that of BDTRh-OH. These bandgap energy differences are shown in Table 1 below.

matter
HOMO
[eV]
LUMO
[eV]
E _g
[eV]
BDTRh-OH
-5.15
-3.55
1.6
BDTRh-PCBM
-5.32
-3.55
1.77

The all-in-one single molecule of the present invention can be prepared by synthesizing BDTRh-OH and PCBM as shown in Scheme 1 below.

Scheme 1

Specifically, BDTRh-OH is synthesized by reacting Compound (1) and Compound (2), and then reacted with Compound (3) ([6,6] -phenyl-C61-butyric acid chloride) to synthesize BDTRh-PCBM. can do.

Compounds (1) and (2) were synthesized by the methods described in the references previously reported (Ailing Tang, Chuanlang Zhan, and Jiannian Yao, Chem . Mater . 2015, 27 , 4719-4730; Christoph Nitsche, Verena N Schreier, Mira AM Behnam, Anil Kumar, Ralf Bartenschlager, and Christian D. Klein, J. Med. Chem., 2013, 56 (21), pp 8389840; Jiaoyan Zhou, Xiangjian Wan, Yongsheng Liu, Yi Zuo, Zhi Li , Guangrui He, Guankui Long, Wang Ni, Chenxi Li, Xuncheng Su, and Yongsheng Chen.J. Am. Chem. Soc., 2012, 134 (39), pp 1634516351)

Compound (3), a derivative of PCBM, was synthesized by reacting a commercially available PCBM. Synthesis of compound 3 can be found in, for example, Weixiang Jiao, Di Ma, Menglan Lv, Weiwei Chen, Haiqiao Wang, Jin Zhu, Ming Lei and Xiwen Chen, J. Mater. Chem. A 2014, 2 (35), 14720-14728; Proceed according to).

According to a preferred embodiment, the present invention provides an organic solar cell comprising the all-in-one single molecule. The organic solar cell includes a first electrode formed on a substrate, a second electrode formed to face the first electrode, one or more organic material layers formed between the first electrode and the second electrode and including a photoactive layer. The photoactive layer includes the all-in-one single molecule. The all-in-one monomolecule is characterized by including both an electron donor and an electron acceptor in one molecular structure.

The substrate may be a glass substrate or a transparent plastic substrate having excellent transparency, surface smoothness and waterproofness, and is not particularly limited as long as it is a substrate commonly used in organic solar cells. Specifically, there are glass or polyethylene terephtalate (PET), polyethylene naphthalate (PEN), polypropylene, polyimide, triacetyl cellulose (TAC), and the like.

The first electrode may be made of a transparent and excellent conductive material as an anode electrode. For example, metals or alloys thereof, such as chromium, copper, zinc, etc .; Metal oxides such as zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO) may be used, but are not limited thereto. The method of forming the first electrode is not particularly limited, and may be applied to one surface of the substrate or coated in a film (film) form using sputtering, E-beam, thermal deposition, spin coating, inkjet printing, and gravure printing.

The second electrode is a cathode electrode, and may be, for example, a metal such as aluminum, silver, magnesium, copper, tin, lithium, titanium, potassium, magnesium, calcium, sodium, and lead or an alloy thereof, but is not limited thereto. Do not.

The organic material layer may include a hole transport layer, a hole injection layer, or a layer for simultaneously transporting holes and injecting holes. Alternatively, the organic material layer may include an electron injection layer, an electron transport layer, or a layer for simultaneously performing electron injection and electron transport.

According to an embodiment of the present invention, the organic solar cell may include a first electrode, a hole transport layer, a photoactive layer, an electron transport layer, and a second electrode.

The hole transport layer material is PEDOT: PSS (Poly (3,4-ethylenediocythiophene doped with poly (styrenesulfonic acid), molybdenum oxide (MoO _x ), vanadium oxide (V ₂ O ₅ ), nickel oxide (NiO), and tungsten oxide ( WO _x ) and the like, but is not limited thereto.

The electron transport layer material may be an electron extraction metal oxide, preferably zinc oxide (ZnO), titanium oxide (TiO _x ), LiF, cesium carbonate (Cs ₂ CO ₃ ), and the like, but is not limited thereto.

The photoactive layer comprises an all-in-one single molecule according to the present invention (BDTRh-PCBM).

Hereinafter, the present invention will be described in detail with reference to production examples and examples, but the scope of the present invention is not limited thereto.

Production Example  One: BDTRh -OH synthesis

Compound (1) (0.5 g, 0.3 mmol) is dissolved in dry chloroform (10 mL), and then a few drops of triethylamine are added in a nitrogen atmosphere. Compound (2) (0.3 g, 1.3 mmol) was added, followed by heating under reflux for 12 hours to proceed with reaction. After the reaction, the mixture is cooled to room temperature to precipitate in methanol. The precipitated solid is washed with methanol and purified by silica gel column chromatography (solvent: CH ₂ Cl ₂ / MeOH = 98/2, v / v). The solid obtained after purification is black in color and has a yield of 94%. BDTRh-OH (0.6 g, 94%) ¹ HNMR (500 MHz, CDCl ₃ ): δ (ppm) 7.76 (s, 2H), 7.60 (s, 2H), 7.34 (d, 2H), 7.21 (m, 4H), 7.11 (m, 4H), 7.67 (s, 2H), 4.12 (t, 4H ), 3.67 (t, 4H), 2.94 (t, 4H), 2.82 (t, 4H), 2.77 (t, 4H), 1.78-0.85 (m, 106H); ¹³ CNMR (225 MHz, CDCl ₃ ): δ (ppm) 192.2, 167.5, 145.9, 140.9, 140.8, 139.6, 138.6, 137.6, 137.3, 137.2, 136.8, 135.5, 135.0, 134.6, 130.4, 128.3, 127.8, 127.1, 126.0, 125.5, 124.9, 123.2, 120.3, 119.1 , 62.8, 44.6, 41.5, 37.1, 34.4, 32.7, 32.5, 31.9, 31.8, 30.4, 30.2, 30.0, 29.7, 29.6, 29.5, 29.4, 29.3, 29.2, 29.0, 27.1, 26.9, 26.4, 25.8, 25.2, 23.1 , 22.7, 22.6, 19.7, 14.1, 11.0. HRMS (MALDI): Calcd for C ₁₁ 0 H ₁₄₄ N ₂ O ₄ S ₁₄ , m / z (M ⁺ ) = 2004.7216; Found: 2004.7242.

Production Example  2: BDTRh - PCBM  synthesis

BDTRh (0.15 g, 0.07 mmol) synthesized in Preparation Example 1 and Compound (3) (0.17 g, 0.18 mmol) were dissolved in 10 ml of dichloromethane, and heated to reflux for 12 hours. After lowering the temperature of the mixture to room temperature, the solvent is removed to precipitate in methanol. The solid obtained after the filter is purified by silica gel column chromatography (solvent: CH ₂ Cl ₂ ). The solid obtained after purification is black in color and has a yield of 42%. BDTRh-PCBM (0.1 g, 42%) ¹ HNMR (500 MHz, CDCl ₃ ): δ (ppm) 7.94 (m, 4H), 7.74 (br, 2H), 7.62 (br, 2H), 7.56 (m, 4H), 7.50 (m, 2H), 7.35 (br, 2H), 7.21 (br, 4H ), 7.12 (br, 4H), 6.97 (br, 2H), 4.08 (br, 8H), 2.92 (br, 8H), 2.79 (br, 8H), 2.53 (br, 4H), 2.21 (br, 4H) , 1.80-0.80 (m, 126H); ¹³ C NMR (225 MHz, CDCl ₃ ): δ (ppm) 192.1, 173.1, 167.4, 148.8, 147.8, 146.0, 145.8, 145.12, 145.1, 145.0, 144.9, 144.7, 144.5, 144.4, 144.3, 143.9, 143.7, 143.1 , 143.0, 142.9, 142.8, 142.2, 142.1, 142.0, 140.9, 140.7, 139.6, 138.0, 137.6, 137.5, 137.4, 136.7, 135.6, 135.2, 134.7, 132.1, 130.4, 128.4, 128.2, 127.8, 127.3, 126.2, 125.5 , 125.0, 123.3, 120.4, 119.2, 79.8, 64.5, 51.8, 44.54, 41.5, 34.4, 34.2, 33.6, 32.5, 31.9, 31.8, 30.4, 30.3, 29.7, 29.6, 29.5, 29.4, 29.3, 29.2, 28.9, 28.4 , 26.9, 26.3, 25.8, 25.6, 23.1, 22.7, 22.4, 14.3, 14.1, 11.0. HRMS (MALDI): Calcd for C ₂₅₂ H ₁₆₄ N ₂ O ₆ S ₁₄ , m / z (M ⁺ ) = 3760.8679; Found: 3760.8632.

Example 1 ITO / PEDOT: PSS / Photoactive Layer / ZnO / Al Device Fabrication

The ITO substrate was cleaned sequentially by ultrasonication using distilled water, acetone and isopropanol. PEDOT: PSS was spin coated onto an ITO substrate and annealed at 140 ° C. for 10 minutes. BDTRh-OH: PCBM (1.1: 1, mixed weight ratio) and BDTRh-PCBM were each mixed in chlorobenzene (15 mg / ml). The mixed weight ratio of 1.1: 1 is calculated from the 1: 2 molar ratio of donors and acceptors of BDTRh-PCBM. The photoactive layer was spin-cast on top of the PEDOT: PSS layer in an N ₂ filled glove box. ZnO nanoparticles were synthesized by the method described in WJE Beek, MM Wienk, M. Kemerink, X. Yang, RAJ Janssen, J. Phys. Chem. B, 2005, 109, 9505 and dispersed in methanol. ZnO solution was spin coated on top of the photoactive layer in an N ₂ filled glove box. Subsequently, the device was pumped under vacuum (<10 ⁶ Torr) and Al (100 nm) was deposited by back evaporation. The area of the Al electrode was 13.0 mm ² .

The measurement results of the organic solar cell thus manufactured are shown as a blend device when the photoactive layer is a BDTRh-OH: PCBM blend and an all-in-one when the photoactive layer is BDTRh-PCBM. -one) expressed as a device.

Experimental Example : How to measure

In the present invention, the following measurements were performed in a glove box using a high quality optical fiber guiding light to a sample in a solar simulator. JV characteristics were collected with a Keithley 2635A source measurement device. Openings made of thin metal (13.0 mm ² ) were attached for measuring photovoltaic properties under an AM 1.5G illuminance of 100 mW / cm ² . EQE measurements were performed using a PV measurement QE system using the monochromatic light of a xenon lamp at ambient conditions. Monochromatic light was cut at 100 Hz and intensity was measured against a standard Si photodiode using a lock-in-amp.

Photovoltaic cell parameters of the two organic solar cells manufactured in Example 1 are shown in Table 2 below.

Photoactive layer J _SC
[mA cm ^-2 ] V _OC
[V] FF PCE
[%] Blend 5.20 0.86 0.52 2.31 All-in-one 7.02 0.97 0.36 2.44

In Example 1, ZnO was used as the electron transport layer. The ZnO layer is known as an electron transport layer that simultaneously increases the short-circuit current density ( J _SC ) and the fill-factor (FF) of the all-in-one monomolecular organic solar cell of the present invention.

In order to optimize the production conditions of the photoactive layer consisting of all-in-one monomolecules, the inventors have tried several treatments such as processing additives, solvent distillation annealing, and thermal annealing which are known in the art. These conventional processes are for controlling the nanoscale morphology of the donor and acceptor domains. The all-in-one monomolecule of the present invention cannot be applied to the device of the present invention because the donor and the acceptor are physically connected as a molecular structure. Therefore, the monomolecular organic solar cell of the present invention was produced without any treatment for the photoactive layer composed of the organic monomolecule. Table 3 below shows the photovoltaic characteristics of the photoactive layer untreated device and the devices treated with the photoactive layer by the conventional method.

In Table 3 below, 0.4 vol% DIO is to control the morphology by adding an additive to the solution, CF vapor annealing is to control the morphology by applying solvent vapor to the film, 80 ℃ thermal annealing is to heat the film to morphology To adjust.

Photoactive layer
process J _SC
[mA cm ^-2 ] V _OC
[V] FF PCE
[%] No treatment (w / o) 7.02
0.97
0.36
2.44 0.4 vol% DIO
3.92
0.27
0.30
0.32 CF vapor annealing
7.19
0.83
0.32
1.91 80 ℃ thermal annealing
6.88
0.96
0.35
2.31

That is, in the present invention, the design of the all-in-one monomolecule is very important for achieving excellent performance in the organic solar cell including the organic monomolecule as the photoactive layer. The organic solar cell according to the present invention has a maximum of 2.44% PCE, and has a high J _sc and V _oc (open circuit voltage) compared to the blended organic solar cell. These data are very high compared to the PCE of the presently reported organic solar cells. Table 4 below compares the photovoltaic properties of the organic solar cells reported in the conventional literatures with those of the organic solar cell according to the present invention.

Document name J _SC
[mA cm ^-2 ] V _OC
[V] FF PCE
[%] EQE (Max.)
[%] J. Mater. Chem.,
2007, 17, 2440 0.93 0.70 0.23 0.15 31
(@ 440nm) Chem. Commun.,
2009, 2469 3.3 0.88 0.44 1.28 40
(@ 440nm) Chem. Commun.,
2011, 47, 6365 4.79 0.51 0.46 1.11 27
(@ 650nm) Phys. Chem. Chem. Phys., 2012, 14, 16138 4.55 0.91 0.46 1.92 45
(@ 450nm) Angew. Chem. Int. Ed., 2016, 55, 12334 6.708 0.663 0.488 2.167 38
(@ 670nm) Example 1 7.02 0.965 0.362 2.44 46
(@ 550nm)

Interestingly, although the two devices fabricated in Example 1 had essentially the same photovoltaic material, the V _oc of the all-in-one device of the present invention increased about 0.1 V compared to the V _oc of the blend device. The external quantum efficiency (EQE) spectra of the blend device and the all-in-one device of the present invention follow the absorption spectra of the thin film with offsets of about 708 nm and about 697 nm, respectively (inset of FIGS. 2B and 2B), which is BDTRh- It is consistent with the bandgap of BDTRh-PCBM which is wider than the bandgap of OH (FIG. 1B). The calculated J _sc based on the EQE spectrum is 5.20 mA cm ⁻² and 6.18 mA cm ⁻² in the blend device and the all-in-one device of the present invention, respectively. The maximum EQE of the all-in-one device is 46% at 420 nm, which is the maximum EQE of the reported single molecule OSCs' EQE (Table 4).

In addition, the light intensity dependence of J _sc and V _oc was measured to investigate charge carrier recombination in the blend device and the all-in-one device of the present invention (FIGS. 2C and 2D). Bi-molecule recombination in the all-in-one device is suppressed by the slope closer to unity in the log-log plot of J _sc versus light intensity (0.9436) compared to the slope for the blend device (0.9078). A semi-logarithmic plot of V _oc versus light intensity shows that the slope of the all-in-one device is closer to kT / q than the slope of the blend device. That means that charge recombination, such as trap-assisted recombination, is suppressed. The all-in-one monomolecular structure can provide a well distributed donor-dock (D / A) interface in the photoactive layer. This can facilitate exciton separation at the donor-receiver (D / A) interface and help improve J _sc in all-in-one devices by reducing the charge recombination of the device as shown in the device results of the present invention (Table 1). .

The low FF of the all-in-one device compared to the FF of the blend device can be deduced from the measurement of JV characteristics in the dark and from the photocurrent J _ph versus effective voltage V _eff (FIG. 3). The leakage current at the reverse bias voltage of the all-in-one device is slightly higher than the leakage current of the blend device, but the rectification ratio of the all-in-one device is lower than that of the blend device. The J _ph vs. V _eff plot was not saturated in both devices, and the plateau region in the plot of the all-in-one device showed higher V _eff compared to the plot of the mixed device. That is, charge collection and extraction to the electrodes are difficult in all-in-one devices compared to blend devices.

In order to investigate the charge carrier transport characteristics of the blend film and the all-in-one film, an organic field effect transistor (OFET) was fabricated (FIG. 4). OFET devices are fabricated with top contact and bottom gate structures. A heavily doped n-type Si substrate was used as the gate electrode, and a thermally grown silicon dioxide (SiO ₂ ) layer was used as the dielectric layer. The SiO ₂ / Si substrates were washed sequentially with acetone and isopropanol and dried in an oven at 100 ° C. for 1 hour. After drying, the substrates were transferred into a glove box filled with N ₂ . BDTRh-OH, BDTRh-OH: PCBM and BDTRh-PCBM layers were spin-cast onto a SiO ₂ layer from solution (15 mg / mL in CB) at 2000 rpm. Ag (70 nm) as source and drain electrodes was thermally evaporated under vacuum (about 10 ⁻⁶ Torr). The interdigitated structure of the source-drain contact determined the channel length (L) of 50 μm and the channel width (W) of 2,950 μm. Electrical properties were measured under nitrogen using a Keithley semiconductor parameter analyzer (Keithley 4200-SCS). The mobility μ is determined using the following equation in the saturation region. Ci is the capacitance per unit area of SiO ₂ dielectric (Ci = 15nF / cm ² ), I _ds is the drain-source current, V _gs is the gate voltage, and Ids is (WCi / 2L) × μ × (Vgs-VT ) V _T is the threshold voltage.

In Figure 4 (a) shows the transfer characteristics of the initial BDTRh-OH (core) OFET and (b) shows the bipolar transfer characteristics of the blend OFET and all-in-one OFET.

The hole mobility of the core and blend (μ _h ) was calculated to be 11.5 x 10 ^-4 cm ² V ^-1 s ^-1 and 9.55 x 10 ^-5 cm ² V ^-1 s ^-1 , respectively, but the hole mobility of the all-in-one is 1.03 × 10 ⁻⁶ cm ² V ⁻¹ s ⁻¹ . The output characteristics of the all-in-one OFET were also worse compared to the output characteristics of the blended OFETs (Figs. 4 (c) and (d)). This indicates that the core portion of the all-in-one monomolecule is less likely to be packed or arranged well in the membrane compared to the blend membrane. Film morphology studies by atomic force microscopy (AFM) and grazing incidence wide angle X-ray scattering (GIWAXS) support this claim.

Space charge limiting current (SCLC) was measured directly in relation to photovoltaic device characteristics to investigate charge carrier mobility in the vertical direction (FIG. 5). Hole-only (ITO / PEDOT: PSS / photoactive layer / Au) and electron-only (fluorine-doped tin oxide (FTO) / photoactive layer / Al) devices were fabricated under the same manufacturing conditions as the photoactive layer. To ensure the accuracy of the measurement, the potential change due to the series resistance ( V _SR ) and the built-in potential ( V _bi ) of the electrode was considered as a correction factor.

All in one film ^{(~ 10 -6 cm 2 V -1} s -1) of the calculated μ _h is the blend layer ^{(~ 10 -7 cm 2 V -1} s -1) than an order of magnitude more high, but the blend film and a film-one E Mobility is shown as about 10 ⁻⁶ cm ² V ⁻¹ s ⁻¹ (Table 5).

Sample μ _h
[cm ² s ^-1 V ^-1 ] μ _e
[cm ² s ^-1 V ^-1 ] μ _e / μ _h Blend 1.92´10 ^-7 2.65´10 ^-6 13.8 All-in-one 1.01´10 ^-6 2.72´10 ^-6 2.69

The ratio of electron-hole mobility between the blend film and the all-in-one film is 13.8 and 2.69, respectively, and the monomolecular organic solar cell exhibits more balanced charge carrier mobility than the bimolecular blend organic solar cell. This supports the high J _sc of monomolecular devices compared to blend devices and certain D / A arrangements can have the advantage of balancing hole and electron charge carrier mobility.

This will be described in detail below.

To understand the V _oc improvement of the all-in-one device, the D / A intermolecular charge transfer (CT) state energy of the blend system and the all-in-one system was investigated. Equation 1 is used to show the EQE spectrum in the CT region and the CT band in FIG. 6 (b).

Where E is photon energy, k is Boltzmann's constant, and T is absolute temperature. The fitting parameter f is a prefactor proportional to the number of states, E _CT is the energy difference of the CT complex ground state with respect to the CT excitation state energy of the CT state, and λ comprises the reconstruction energy term λ ₀ . Related to CT absorption band width (W. Zhao, D. Qian, S. Zhang, S. Li, O. Inganas, F. Gao, J. Hou, Adv Mater 2016, 28, 4734; KR Graham, C. Cabanetos, JP Jahnke, MN Idso, A. El Labban, GO Ngongang Ndjawa, T. Heumueller, K. Vandewal, A. Salleo, BF Chmelka, A. Amassian, PM Beaujuge, MD McGehee, J Am Chem Soc 2014, 136, 9608; NA Ran, JA Love, CJ Takacs, A. Sadhanala, JK Beavers, SD Collins, Y. Huang, M. Wang, RH Friend, GC Bazan, TQ Nguyen, Adv Mater 2016, 28, 1482; K. Vandewal, K. Tvingstedt, A. Gadisa, O. Ingana J. V. Manca, Physical Review B 2010, 81,).

In addition, the energy loss (E _loss ) was obtained by subtracting the band gap energy (Eg ^* ) of the active layer component from E _CT (E _loss = Eg ^* -E _CT ). Eg ^* was extracted from the tauc plot of the blend film and the all-in-one film, which means the excitation energy of the photoactive component (FIG. 6 (a)). The E _CT values of the fit curve are 1.46 eV and 1.56 eV for blend and all-in-one devices, respectively. The empirical relationship between V _oc and E _CT (V _oc E _CT / q-0.6) shows that the measured E _CT values agree with the measured V _oc (Table 1). The E _loss of the all-in-one device is 0.28 eV (= 1.84 eV-1.56 eV), while the energy loss of the blend device is 0.35 eV (= 1.81 eV-1.46 eV). The improvement in V _{oc in} the all-in-one system was achieved by mitigating the energy loss of the D / A CT.

Another fitting parameter λ means uniformity of molecular arrangement and energy state. Low λ indicates the presence of a specific molecular arrangement, which indicates uniformity of the energy state and promotes charge separation. Monomolecular organic solar cells (OSCs) have a lambda value (0.10 eV) lower than the lambda (0.23 eV) of a two-molecule blend device. In other words, the all-in-one molecular structure has the advantage of constituting specific D / A arrays that can alleviate energy disturbances.

Steady-state photoluminescence (PL) was recorded in BDTRh-OH, BDTRh-OH: PCBM blends and BDTRh-PCBM to study exciton recombination and charge transfer. The excitation energy to excite most of the BDTRh component in the blend system and all-in-one system was 2.17 eV (FIG. 7A). The photoluminescence (PL) spectra of pure BDTRh-OH, BDTRh-OH: PCBM blend and BDTRh-PCBM are shown in Figure 7 (b). In the comparison of the BD spectrum of the BDTRh-OH: PCBM blend membrane with the BDTRH-OH membrane, the PL emission was nearly quenched (94.8%). In addition, the PL in the all-in-one system was also fully quenched (96.4%) compared to BDTRh-OH. Both observations indicate that there is an efficient electron transfer from BDTRh to PCBM as well as the blend system in BDTRh-PCBM (also supported by the transient absorption data described below).

Femtosecond Instantaneous Absorption Spectroscopy (TAS) was performed on BDTRh-OH, BDTRh-OH: PCBM blends and BDTRh-PCBM to track the exciton and charge generation kinetics. In this experiment, a 2.17 eV pump photon is used to selectively excite the BDTRh component, and the final dynamics are monitored by measuring the differential transmission of the broadband probe pulses in the near infrared region of the spectrum at different time delays after excitation. 8 (a) shows the TAS of the pure BDTRh-OH membrane at different time delays. A broad negative band centered at 1.1 eV and a positive band centered at 1.5 eV are observed. This band (peak) is consistent with the absorption and stimulus release of the BDTRh-OH singlet excitons, respectively. The dynamics of the negative bands are shown in Figure 8 (b). BDTRh-OH singlet excitons decay with a lifetime of 20 ps (1 / e time).

9A and 9B show the TAS of the BDTRh-OH: PCBM blend and BDTRh-PCBM at different time delays. In addition to the exciton band ˜1 eV, a strong polaron band was observed in both samples at 1.4 eV. The properties of the exciton and polaron photo-induced absorption (PIA) spectra are consistent with the initial TAS results in the polymer blend. 9C and 9D show the change over time of the TAS signal at ˜1.03 eV and ˜1.4 eV for BDTRh-OH: PCBM blend and BDTRh-PCBM films. Singlet excitons undergo ultrafast charge transfer in both samples, as indicated by the rapid attenuation of the singlet exciton bands to 1.03 eV. The singlet exciton decay time (2 ps) for the BDTRh-OH: PCBM blend is much faster than the BDTRh-OH film (20 ps) and shows high efficiency of photo induced charge transfer. We also observed an instantaneous signal increase of the 1.03 eV peak at the delay. We also monitored the dynamics of the Polaron peak ~ 1.4 eV. The polaron lifetime of this blend is 350 ps (1 / e hour). The electron transfer time in BDTRh-PCBM is 300 fs and the polaron lifetime (3.5 ns) is a longer order compared to BDTRh-OH: PCBM. The instantaneous signal at 1.03 eV also increases after 1 ps and rises to 1 ns.

To understand the cause of this rise, a light source intensity dependent TAS was performed in FIG. 10. We then observed the intensity dependent kinetics of the 1.03 eV peak (FIGS. 10A and 10B). We believe that through electron and hole recombination, this contributed to the generation of triplet excitons. However, the initial kinetics at 1.03 eV are independent of light intensity, which means that there is no exciton disappearance in our measurements. We also observed strong light source intensity dependence of polaron peak breakdown, corresponding to bimolecular recombination of free charge (FIGS. 10 (c) and 10 (d)). Non-double recombination of charge increases with increasing light intensity (0V bias) because no charge is extracted in these measurements. At similar optical excitation densities, triplet formation is very strong in BDTRh-PCBM compared to BDTRh-PCBM blends.

The surface morphology of the blend and all-in-one film is compared by tapping atomic force microscopy (AFM). The phase image corresponding to the morphological image is shown in FIG. 11. The blend membrane clearly distinguishes the BDTRh-OH and PCBM domains, and the all-in-one membrane has a well distributed plane. Structurally connected donors and rests were self-inhibited in all-in-one systems, but self-aggregation of donors and rests appeared in the blend system. In addition, the root-mean-square (RMS) value of the surface roughness shows a high difference between the two films, 16.7 nm for the blend film and 0.405 nm for the all-in-one film. This means that the molecular design leads to a specific D / A arrangement, which is consistent with the λ estimate of FIG. 6B.

Coarse low-incidence wide-angle X-ray scattering (GIWAXS) measurements are available for detailed analysis of molecular packing on pristine BDTRh-OH (core) membranes and BDTRh-PCBM (all-in-one) membranes, and BDTRh-OH: PCBM (blend) membranes. Was performed (FIG. 12). The packing parameters derived from the GIWAXS measurements are summarized in Table 6.

Direction
Sample
Lamellar stack π-π stack Scattering vector (q)
[Å- ¹ ] d-spacing
[Å] Scattering vector (q)
[Å- ¹ ] d-spacing
[Å]
In-plane Core 0.2981 21.08 1.697 3.703 Blend 0.2941 21.36 1.675 3.750 All-in-one 0.3080 20.40 - -
Out-of-plane Core 0.3069 20.47 1.668 3.767 Blend 0.2950 21.29 - - All-in-one 0.3208 19.58 - -

The original core membrane has strong out-of-plane scattering peaks up to third order 300 and π-π stacking peaks 010 in both in-plane and out-of-plane directions. The feature remains in the blend film, ie BDTRh-OH freely forms a domain in the PCBM domain. All-in-one membranes, on the other hand, have a weaker interlamellar packing 100 compared to core and blend membranes. In BDTRh-PCBM, two connected PCBMs interfere with the molecular packing of the core. This feature is consistent with the AFM results. The reason why the FF is lowered in the all-in-one device may be that it is difficult to form the donor domain itself in the all-in-one system although it is appropriate to form a specific molecular arrangement. In other words, the molecular design of all-in-one photovoltaic small molecules is still struggling to find out how each of the dorsal and dorsal forms their domains.

In conclusion, the present invention successfully proposes a monomolecular organic solar cell using all-in-one monomolecules. PCE 2.44% is the highest reported PCE among all-in-one mono-molecule organic solar cells. The present invention also presents the advantages of an all-in-one system as compared to a bimolecular blend system. In all-in-one systems, energy losses through the CT process are significantly reduced, providing improved V _OC in monomolecular organic solar cells. Obvious differences in lambda values indicate that all-in-one systems are advantageous for forming specific molecular configurations at the D / A interface by structurally connected donors and acceptors. In addition, the all-in-one system exhibited high polaron properties, ultrafast electron transfer, and strong triplet formation. These results suggest that, despite efficient charge generation in a very short time in all-in-one systems, low mobility limits the improvement of optical power performance. There are still some challenges to achieving high performance monomolecular organic solar cells because donors and receivers are difficult to form their own domains in all-in-one systems. However, the present invention, together with the blended organic solar cell for the optimization of monomolecular organic solar cell, can be evaluated that the emergence of a new type of device: the monomolecular OSC has opened a new way to research and development of the OSC.

Claims (13)

As an organic single molecule having a [ADA] structure,
A is a compound derived from PCBM,
D is a compound containing benzo [1,2- b : 4,5- b ' ] dithiophene (benzo [1,2- b : 4,5- b' ] dithiophene, BDT) as a central unit,
The organic single molecule is a compound of formula
The organic single molecule is an organic single molecule synthesized by reacting BDTRh-OH of [Formula 3] with [6,6] -phenyl-C61-butyric acid chloride.
[Formula 1]

[Formula 3]

The organic single molecule according to claim 1, wherein A is an electron acceptor, and D is an electron donor. The organic single molecule according to claim 1, wherein the molar ratio of D: A is 1: 2. An organic solar cell comprising a first electrode formed on a substrate, a second electrode formed to face the first electrode, and at least one organic material layer formed between the first electrode and the second electrode and including a photoactive layer.
The photoactive layer includes an organic solar cell including an organic single molecule having a [ADA] structure;
A is a compound derived from PCBM,
D is a compound containing benzo [1,2- b : 4,5- b ' ] dithiophene (benzo [1,2- b : 4,5- b' ] dithiophene, BDT) as a central unit,
The organic single molecule is a compound of the formula
The organic single molecule is synthesized by reacting BDTRh-OH of [Formula 3] with [6,6] -phenyl-C61-butyric acid chloride.
[Formula 1]

[Formula 3]

The organic solar cell of claim 4, wherein A is an electron acceptor, and D is an electron donor. The organic solar cell of claim 4, wherein the molar ratio of D: A is 1: 2. The organic solar cell of claim 4, wherein the organic material layer includes a hole transport layer, a hole injection layer, or a layer for simultaneously transporting holes and injecting holes. The organic solar cell of claim 4, wherein the organic material layer includes an electron injection layer, an electron transport layer, or a layer for simultaneously injecting and transporting electrons. The organic solar cell of claim 4, wherein the organic solar cell includes a first electrode, a hole transport layer, a photoactive layer, an electron transport layer, and a second electrode. The material of claim 9, wherein the material of the hole transport layer is PEDOT: PSS (Poly (3,4-ethylenediocythiophene doped with poly (styrenesulfonic acid), molybdenum oxide (MoO _x ), vanadium oxide (V ₂ O ₅ ), nickel oxide ( NiO), and tungsten oxide (WO _x ) is one selected from the group consisting of organic solar cells. The organic solar cell of claim 9, wherein the material of the electron transport layer is one selected from the group consisting of zinc oxide (ZnO), titanium oxide (TiO _x ), LiF, and cesium carbonate (Cs ₂ CO ₃ ). The organic solar cell of claim 4, wherein the first electrode comprises one selected from the group consisting of chromium, copper, zinc, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO). battery. The organic solar cell of claim 4, wherein the second electrode is one selected from the group consisting of aluminum, silver, magnesium, copper, tin, lithium, titanium, potassium, magnesium, calcium, sodium, and lead.

Images