Performance Of Bulk Heterojunction Solar Cells Research Articles

Improving morphology of P3HT:PCBM bulk heterojunction solar cells with anisotropic shaped silica nanoparticles

Using coarse-grained molecular dynamics simulations we study blends of Poly(3-hexylthiophene-2,5-diyl) (P3HT), [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) and Silica nanoparticle (SiNP) to understand the effect of adding SiNP on morphology of P3HT:PCBM in Bulk heterojunction (BHJ) solar cells. We use an approximately 3 nm anisotropic shaped SiNP and predicted the morphology of BHJ upon its incorporation. The SiNP arrange themselves into anisotropic structures depending on the concentration of P3HT, PCBM and SiNP respectively creating a network like morphology. PCBM molecules utilize the surface energy of SiNP and gather at its surface forming a morphology which is beneficial for device efficiency. Our results suggest that an optimum weight fraction of all the three components leads to higher surface area of contact, optimum domain size and high percolation of domains throughout the system. The effective control of all the morphological parameters help in improving the charge generation, extraction and transport to electrodes, thereby improving the performance of BHJ solar cells.

Photovoltaic Characterization of Hybrid Bulk Heterojunction Solar Cell Incorporated Gold Nanoparticles Embedded in Active Layer

We attempt to study the effect of gold nanoparticles embedded into the active polymer of regioreguler poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) on the charge kinetic to enhance the performance of bulk-heterojunction solar cell. It has been known that the generation of localized surface plasmon resonance (LSPR) would both increase the photon absorption and improve the efficiency of charge separation. Synthesis of gold nanoparticles stabilized by oleylamine (AuOA) was carried out by reduction method and resulted in the spherical shape of nanoparticles with a diameter size of ~12 nm. The absorbance spectra show the typical of surface plasmon peak of AuOA in solution at ~527 nm. Fabrication of inverted bulk-heterojunction solar cell device was done in the configuration of ITO/ZnO/P3HT:PCBM:AuOA/PEDOT:PSS/Ag. Incorporation of AuOA in polymer solution is clearly detected from the enhanced absorbance peak resulted from UV-Vis measurement and the mix solution of P3HT:PCBM:AuOA is quite stable in the concentration of AuOA less than 10 wt%. In our experiment, fabricated solar cell reveals the enhancement in current density at short circuit condition (Jsc) from 44.57 mA/cm2 to 56.14 mA/cm2 with the addition of 3.9 wt% AuOA in polymer solution along with the enhancement of power conversion efficiency (PCE) from 4.07% to 6.23% as characterized by J-V measurement. In our case, the voltage at open circuit condition (Voc) of the device does not show significant improvement.

Optoelectronic properties of cyclopentadithiophene-based donor–acceptor copolymers as donors in bulk heterojunction organic solar cells: A theoretical study

Cyclopentadithiophene and benzothiadiazole derivatives have promising characteristics for use in organic solar cells. In this study, we theoretically investigated two donor–acceptor copolymers comprising 2-(benzo[c][1,2,5]thiadiazol-4-yl)-4H-cyclopenta[2,1-b:3,4-b']dithiophen-4-one and 2-(2-(benzo[c][1,2,5]thiadiazol-4-yl)-4H-cyclopenta[2,1-b:3,4-b']dithiophen-4-ylidene)malononitrile with alternating donor–acceptor building units. Different copolymer chain lengths (n = 1–5) were extended to investigate their structural, electronic, and photo-physical properties based on density functional theory calculations. The copolymers exhibited high planarity, reduced band gap energies, and broad absorption in the visible range, and thus they may enhance the performance of organic solar cells. The transition density matrix plots were simulated for the copolymers and used to evaluate hole–electron localization interactions, donor–acceptor interactions, and the electronic excitation processes in their excited states. The charge transfer properties, fill factors, and open-circuit voltages were estimated. Based on our simulations, we found that the trimer was the most suitable conformation among the copolymers for designing high performance bulk heterojunction (BHJ) solar cells. The power conversion efficiency of the BHJ-based blended copolymers-[70]PCBM was estimated as 9.5%. Thus, the appropriate design of conjugated materials could considerably enhance the donor properties to further improve the performance of BHJ solar cells.

In-depth investigation of the charge extraction efficiency for thermally annealed inverted bulk-heterojunction solar cells

The performance of bulk-heterojunction solar cells is significantly affected by several factors among which are the nano-morphology of the photoactive layer and the properties of interfacial layers promoting charge extraction and collection at the electrodes. In this work, we investigate the correlation between the MoOx layer thickness and the thermal annealing procedure on the device performance and on the charge extraction efficiency of inverted ITO/PEI/P3HT:PCBM/MoOx/Ag bulk heterojunction solar cells. The surface morphology of pristine and annealed P3HT:PCBM photoactive layers is examined by atomic force microscopy before and after the exposure to dichloromethane revealing that the distribution of the amorphous regions within the P3HT:PCBM layers can be related to the applied thermal annealing procedure. The chemical and molecular composition profiles in the photoactive layer and at the interfaces are investigated through depth profile analyses combining X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry showing a decreasing oxidation gradient of the MoOx and low diffusion of the MoOx species in the P3HT:PCBM layer. Additionally, we show that the voltage dependent photocurrent is significantly affected by non-geminate recombination for devices with a too thin MoOx layer thickness, while applying a non-optimal thermal annealing procedure leads to increased geminate recombination of charge carriers. The highest charge extraction efficiency and device performance is reached for devices with a MoOx layer above 5 nm while thermal annealing procedure has to be applied before the deposition of the MoOx/Ag layers.

Effects of neat C60 doping on the performance of bulk-heterojunction solar cells based on P3HT:PCBM

ABSTRACTWe explored the effect of neat C60 doping on the performance of bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). The power conversion efficiencies (PCEs) were found to gradually decrease as the relative concentration of C60 increased. This PCE decrease is mainly due to the reduction in short-circuit current density (Jsc). Atomic force microscopy images revealed that C60-doped BHJ films consisted of unformed large P3HT crystals and many small PCBM aggregates. This morphology leads to a decrease in the effective P3HT conjugation length and an enhancement of absorption bleaching in neutral P3HT chains. These results explain well the blue-shift absorption spectra, the decrease of absorption coefficients, and the reduction in Jsc found in C60-doped BHJ OPVs.

The Study of Crystallization of Polyfluorene and Fullerene Derivatives in Semiconducting Layer of Organic Solar Cells

This research was focused on the effect of solid crystallization additive namely 1,4-dichlorobenzene (PDCB) in the 1:2 (w/w) active layer of benzothiadiazole/thiophene-based copolymers (PFTBzTT) to [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) on the morphology and performance of bulk heterojunction (BHJ) organic solar cells. The active layer was deposited by spin-coating with chloroform solutions by different PDCB additive concentrations from 0-52 mg/ml. The inclusion of additive into the polymer solution was able to improve the performance of BHJ solar cells. The maximum power conversion efficiency (PCE) of 0.84% achieved for a cell with PDCB concentration of 36 mg/ml after annealing at 180 °C for 20 min. The XRD and TEM techniques used to analyse the crystal structure and morphology of the thin films. From these results were found that PDCB additive presented higher level of PCBM crystal structure by more aggregation of PCBM and a larger extent of phase separation than those of the films without additive. The AFM results demonstrated that the optimum PDCB concentration and annealing process helped PCBM aggregated into micron sized crystal rods.

Donor and Acceptor Unit Sequences Influence Material Performance in Benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐Difluoroquinoxaline Small Molecule Donors for BHJ Solar Cells

Well‐defined small molecule (SM) donors can be used as alternatives to π‐conjugated polymers in bulk‐heterojunction (BHJ) solar cells with fullerene acceptors (e.g., PC61/71BM). Taking advantage of their synthetic tunability, combinations of various donor and acceptor motifs can lead to a wide range of optical, electronic, and self‐assembling properties that, in turn, may impact material performance in BHJ solar cells. In this report, it is shown that changing the sequence of donor and acceptor units along the π‐extended backbone of benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐difluoroquinoxaline SM donors critically impacts (i) molecular packing, (ii) propensity to order and preferential aggregate orientations in thin‐films, and (iii) charge transport in BHJ solar cells. In these systems (SM1‐3), it is found that 6,7‐difluoroquinoxaline ([2F]Q) motifs directly appended to the central benzo[1,2‐b:4,5‐b′]dithiophene (BDT) unit yield a lower‐bandgap analogue (SM1) with favorable molecular packing and aggregation patterns in thin films, and optimized BHJ solar cell efficiencies of ≈6.6%. 1H‐1H DQ‐SQ NMR analyses indicate that SM1 and its counterpart with [2F]Q motifs substituted as end‐group SM3 possess distinct self‐assembly patterns, correlating with the significant charge transport and BHJ device efficiency differences observed for the two analogous SM donors (avg. 6.3% vs 2.0%, respectively).

π-Bridge-Independent 2-(Benzo[c][1,2,5]thiadiazol-4-ylmethylene)malononitrile-Substituted Nonfullerene Acceptors for Efficient Bulk Heterojunction Solar Cells

Molecular acceptors are promising alternatives to fullerenes (e.g., PC61/71BM) in the fabrication of high-efficiency bulk-heterojunction (BHJ) solar cells. While solution-processed polymer–fullerene BHJ devices have recently met the 10% efficiency threshold, molecular acceptors have yet to prove comparably efficient with polymer donors. At this point in time, it is important to forge a better understanding of the design parameters that directly impact small-molecule (SM) acceptor performance in BHJ solar cells. In this report, we show that 2-(benzo[c][1,2,5]thiadiazol-4-ylmethylene)malononitrile (BM)-terminated SM acceptors can achieve efficiencies as high as 5.3% in BHJ solar cells with the polymer donor PCE10. Through systematic device optimization and characterization studies, we find that the nonfullerene analogues (FBM, CBM, and CDTBM) all perform comparably well, independent of the molecular structure and electronics of the π-bridge that links the two electron-deficient BM end groups. With estimated...

Synthesis and characterization of two fluorenone-based conjugated polymers and their application in solar cells and thin film transistors

Two new fluorenone-based conjugated polymers, F1 and F2, were synthesized via the Stille cross-coupling polymerization. Spectral measurements showed that both polymers had optical band gaps of 1.99eV and 1.89eV, respectively, calculated based on the film onset absorption edge. Cyclic voltammetric studies gave HOMO/LUMO energy levels of −5.18eV/−3.19eV and −5.40eV/−3.51eV, respectively, and the polymers were thermally stable at temperatures over 300°C. Organic field-effect transistor and bulk-heterojunction solar cell performance characteristics of both polymers as p-type semiconductors were evaluated.

Understanding the morphology of solution processed fullerene-free small molecule bulk heterojunction blends.

Bulk-heterojunction (BHJ) molecular blends prepared from small molecules based on diketopyrrolopyrrole (DPP) and perylene-diimide (PDI) chromophores have been studied using optical absorption, cyclic voltammetry, photoluminescence quenching, X-ray diffraction, atomic force microscopy, and current-voltage measurements. The results provided useful insights into the use of DPP and PDI based molecules as donor-acceptor composites for organic photovoltaic (OPV) applications. Beside optoelectronic compatibility, the choice of active layer processing conditions is of key importance to improve the performance of BHJ solar cells. In this context, post-production treatments, viz. thermal and solvent vapour annealing, and the use of 1,8-diiodooctane as a solvent additive were employed to optimize the morphology of blend films. X-ray diffraction and atomic force microscopy indicated that the aforementioned processing strategies led to non-optimal composite morphologies with significantly large crystallites in comparison to exciton diffusion lengths. Although the open circuit voltage of the OPV devices was satisfactory (0.78 V), it was anticipated that the bulky domains hamper charge dissociation and transport, which resulted in low photovoltaic performance.

Controlling the morphology of the active layer by using additives and its effect on bulk hetero-junction solar cell performance

-Improvement of the surface roughness and power conversion efficiency (PCE) of bulk hetero-junction (BHJ) solar cells was made by the addition of organic additives for the cells based on a low energy-gap polymer, poly [2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b'] dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), as an electron donor and [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) as the electron acceptor. The PCPDTBT: PC61BM active layers were prepared by spin-coating process from four different organic solvents: pure chlorobenzene, chlorobenzene with 2.5 vol% 1,2-ethanedithiol (EDT) additive, chlorobenzene with 2.5 vol% 1,8-octanedithiol (ODT) additive, and chlorobenzene with a combination of 2.5 vol% EDT and 2.5 vol% ODT additives. The smoothest surface of the active layer, which was observed by AFM, was obtained in the case of PCPDTBT:PC61BM prepared with a combination of EDT and ODT additives in chlorobenzene, and a maximum PCE of 3.5% was achieved.

Ternary Blend Bulk-Heterojunction Solar Cells Based on Active Layers of PTB7, PC71BM, and PC61BM

Organic bulk-heterojunction (BHJ) solar cells are highly efficient solar cells with additional advantages such as low-cost production, large area, and mechanical flexibility, as they can be fabricated by solution processing without using high vacuum equipment [1]. On the other hand, an extremely high PCE of 7.5% has recently been reported for BHJ solar cells by Murray et al. [2]. The cells were fabricated using a p-type semiconductor, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7), an n-type semiconductor, [6,6]-phenyl-C71-butyric-acid-methyl-ester (PC71BM), and a lithium fluoride (LiF) inserted Al cathode on an indium tin oxide (ITO) coated glass substrate. These promising results inspired many recent studies on BHJ solar cells based on PTB7:PC71BM, and various techniques were proposed to further improve the performance of the BHJ solar cells. Ternary or quaternary blend solar cells have also been reported to exhibit interesting performances. Lin et al. [3] have demonstrated a significant improvement in PCE by adding the PTB7 polymer to a poly[[4,8-bis[(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-bnodithiophene-2,6-diyl]] (PCD TBT):PC71BM host system in order to form a ternary-blend BHJ solar cell; the addition of 5 wt% of PTB7 resulted in the greatest PCE improvement. Such studies on ternary-blend solar cells showed performance improvements as a result of adding minute amounts of additives to the host active layers. Ohori et al. recently reported significant improvements in the performance of BHJ solar cells based on ternary-blend organic semiconductor materials with smaller amounts of P3HT additives into the PTB7:PC61BM active layers [4]. They suggested that the improvement of their solar cells was due to enhanced carrier transport paths. Xu et al. reported a significant increase in the open-circuit voltage (Voc) of quaternary-blend BHJ solar cells based on P3HT as a donor, and PC61BM, indene-C60 bisadduct (ICBA) and silicon phthalocyanine bis(trihexylsilyl oxide) as acceptors [5]. Cheng et al. fabricated ternary blend BHJ solar cells based on PTB7:ICBA:PC71BM, and found that the solar cells showed the maximum PCE at the ICBA weight fraction of 15% of the total weight of ICBA and PC71BM [6]. They suggested that the PCE improvement was due to the cascade electron transfer through the lowest unoccupied molecular orbital (LUMO). Notably, ternary blend solar cells based on PTB7, PC61BM, and PC71BM may have similar LUMO cascade structures, but they have not yet been reported. In this paper, we report on BHJ solar cells based on ternary blend solutions of PTB7, PC71BM, and PC61BM. Bulk-heterojunction solar cells were fabricated using ternary blend dichlorobenzene solutions of poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) with different weight ratios between PC61BM and PC71BM. In all the solar cells, the overall weight ratio of polymer to fullerene was maintained at 1:1.5, while the composition of the fullerene component (PC61BM:PC71BM) was varied. The ultraviolet-visible absorption spectra of these ternary blend films showed that the photon absorptions at wavelengths between 300 and 800 nm continuously decreased with the increase of the PC61BM weight fraction in the PC61BM and PC71BM total weight. The measurement results of the solar cell performance showed that the open-circuit voltage notably increased for PC61BM weight fractions between 10% and 90%, while it decreased at 100%. The short-circuit current showed the most significant increase in the PC61BM weight fraction range between 50% and 60%. A power conversion efficiency of 3.4% was achieved when the PC61BM weight fraction was between 50% and 60%. These results may suggest that the transport of the photoexcited electrons between the cathode and the PC61BM/PC71BM nanodomains was enhanced. [1] C. J. Brabec, N. S. Sariciftci, and J. C. Hummelen, Adv. Funct. Mater., 11 (2001) 15. [2] I. P. Murray, S. J. Lou, L. J. Cote, S. Loser, C. J. Kadleck, T. Xu, J. M. Szarko, B. S. Rolczynski, J. E. Johns, J. Huang, L. Yu, L. X. Chen, T. J. Marks, and M. C. Hersam, J. Phys. Chem. Lett., 2 (2011) 3006. [3] R. Lin, M. Wright, B. P. Veettil, and A. Uddin, Synth. Met., 1927 (2014) 113. [4] Y. Ohori, S. Fujii, H. Kataura, and Y. Nishioka, Jpn. J. Appl. Phys., 45 (2015) 04DK09. [5] H. Xu, H. Ohkita, H. Benten, and S. Itoh, Jpn. J. Appl. Phys., 53 (2014), 01AB10. [6] P. Cheng, Y. Li, and X. Zhan, Energy Environ. Sci., 7 (2014) 2005.

Improvement in PbS-based Hybrid Bulk-Heterojunction Solar Cells through Band Alignment via Bismuth Doping in the Nanocrystals.

We introduce dopants in lead sulfide (PbS) quantum dots (QDs) in forming hybrid bulk-heterojunction (BHJ) solar cells. Because an increase in the content of bismuth as dopants in PbS QDs transforms the intrinsic p-type semiconductor into an n-type one, the band alignment between a conjugated polymer and the doped QDs changes upon doping affecting performance of BHJ solar cells. From scanning tunneling spectroscopy (STS) of the doped QDs, we observe a shift in their Fermi energy leading to formation of a type II band alignment in the polymer:doped-QD interface. We also show that the dopants improve electron-conduction process through the QDs. With the dopants controlling both band alignments at the interface and the conduction process, we show that the dopant concentration in QDs influences open-circuit voltage unfavorably and short-circuit current in a beneficial manner. The device performance of hybrid BHJ solar cells is hence maximized at an optimum concentration of bismuth in PbS QDs.

Effect of the Side Chains and Anode Material on Thermal Stability and Performance of Bulk-Heterojunction Solar Cells Using DPP(TBFu)2Derivatives as Donor Materials

An optimized fabrication of bulk-heterojunction solar cells (BHJ SCs) based on previously reported diketopyrrolopyrrole donor, ethyl-hexylated DPP(TBFu)2, as well as two new DPP(TBFu)2derivatives with ethyl-hexyl acetate and diethyl acetal solubilizing side-chains and PC60BM as an acceptor is demonstrated. Slow gradual annealing of the solar cell causing the effective donor-acceptor reorganization, and as a result higher power conversion efficiency (PCE), is described. By replacing a hole transporting layer PEDOT:PSS with MoO3we obtained higher PCE values as well as higher thermal stability of the anode contact interface. DPP(TBFu)2derivative containing ethyl-hexyl acetate solubilizing side-chains possessed the best as-cast self-assembly and high crystallinity. However, the presence of ethyl-hexyl acetate and diethyl acetal electrophilic side-chains stabilizes HOMO energy of isolated DPP(TBFu)2donors with respect to the ethyl-hexylated one, according to cyclic voltammetry.

Effects of cyano-substituents on the molecular packing structures of conjugated polymers for bulk-heterojunction solar cells.

The molecular packing structures of two conjugated polymers based on alkoxy naphthalene, one with cyano-substituents and one without, have been investigated to determine the effects of electron-withdrawing cyano-groups on the performance of bulk-heterojunction solar cells. The substituted cyano-groups facilitate the self-assembly of the polymer chains, and the cyano-substituted polymer:PC71BM blend exhibits enhanced exciton dissociation to PC71BM. Moreover, the electron-withdrawing cyano-groups lower the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the conjugated polymer, which leads to a higher open circuit voltage (V(OC)) and a lower energy loss during electron transfer from the donor to the acceptor. A bulk-heterojunction device fabricated with the cyano-substituted polymer:PC71BM blend has a higher V(OC) (0.89 V), a higher fill factor (FF) (51.4%), and a lower short circuit current (J(SC)) (7.4 mA/cm(2)) than that of the noncyano-substituted polymer:PC71BM blend under AM 1.5G illumination with an intensity of 100 mW cm(-2). Thus, the cyano-substitution of conjugated polymers may be an effective strategy for optimizing the domain size and crystallinity of the polymer:PC71BM blend, and for increasing V(OC) by tuning the HOMO and LUMO energy levels of the conjugated polymer.

ChemInform Abstract: Near Infrared Organic Semiconducting Materials for Bulk Heterojunction and Dye‐Sensitized Solar Cells

AbstractReview: [274 refs.

The Effect of Band-Bending on Hybrid Bulk Heterojunction Solar Cell Performance

Hydrid bulk heterojunction solar cells (HBHJs) consist of nanostructured metal oxide (TiO2 and ZnO) acceptors and polymer light absorbing donors. To date, these promising architectures have only achieved moderate efficiency due to surprisingly low short circuit photocurrents. To elucidate the underlying properties that result in this low current, a detailed understanding of interfacial properties is required. Herein, we quantify a vacuum level offset of 0.8 eV between the polymer and the TiO2 created by spontaneous charge transfer upon heterojunction formation. This offset imparts a barrier to charge separation at the TiO2-polymer interface and explains the poor performance of cells to date. New materials for improved photocurrent are proposed by tuning the energetics of the heterojunction.

Near infrared organic semiconducting materials for bulk heterojunction and dye-sensitized solar cells.

Dye sensitized solar cells (DSSCs) and bulk heterojunction (BHJ) solar cells have been the subject of intensive academic interest over the past two decades, and significant commercial effort has been directed towards this area with the vison of developing the next generation of low cost solar cells. Materials development has played a vital role in the dramatic improvement of both DSSC and BHJ solar cell performance in the recent years. Organic conjugated polymers and small molecules that absorb solar light in the visible and near infrared (NIR) regions represent a class of emering materials and show a great potential for the use of different optoelectronic devices such as DSSCs and BHJ solar cells. This account describes the emering class of near infrared (NIR) organic polymers and small molecules having donor and acceptors units, and explores their potential applications in the DSSCs and BHJ solar cells.

Controlling Solution‐Phase Polymer Aggregation with Molecular Weight and Solvent Additives to Optimize Polymer‐Fullerene Bulk Heterojunction Solar Cells

The bulk heterojunction (BHJ) solar cell performance of many polymers depends on the polymer molecular weight (M n) and the solvent additive(s) used for solution processing. However, the mechanism that causes these dependencies is not well understood. This work determines how M n and solvent additives affect the performance of BHJ solar cells made with the polymer poly(di(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐co‐octylthieno[3,4‐c]pyrrole‐4,6‐dione) (PBDTTPD). Low M n PBDTTPD devices have exceedingly large fullerene‐rich domains, which cause extensive charge‐carrier recombination. Increasing the M n of PBDTTPD decreases the size of these domains and significantly improves device performance. PBDTTPD aggregation in solution affects the size of the fullerene‐rich domains and this effect is linked to the dependency of PBDTTPD solubility on M n. Due to its poor solubility high M n PBDTTPD quickly forms a fibrillar polymer network during spin‐casting and this network acts as a template that prevents large‐scale phase separation. Furthermore, processing low M n PBDTTPD devices with a solvent additive improves device performance by inducing polymer aggregation in solution and preventing large fullerene‐rich domains from forming. These findings highlight that polymer aggregation in solution plays a significant role in determining the morphology and performance of BHJ solar cells.

C214 シリコンナノ粒子と半導体ポリマーのバルクヘテロジャンクション構造に関する基礎研究

Structure of silicon nanocrystal (Si NC)/semiconductor-polymer (P3HT) bulk heterojunction has been studied by using transmission FTIR and Raman spectroscopy. Chlorine-terminated Si NC (C1:Si NC) and hydrogenterminated Si NC (H:Si NC) were investigated for this purpose. In the case of Cl:Si NC and P3HT blended film, the structure of thiophene, which provides the hole transporting path, is chemically modified. As a result, hole transport property was deteriorated. Additionally, surface doping efficiency of Si NC has been studied by analyzing performance of Si NC thin film transistor. The electron mobility is improved by hydrogen termination. The results suggest that the hybrid Si NC/P3HT bulk heterojunction solar cell performance is improved greatly by hydrogen termination.