| With the constant demand of clean energy and the decrease of fossil oil, it is urgent to develop a new kind of clean energy to meet the need of the new era. Polymer solar cells(PSCs) have received wide attention due to the low processing cost, light weight, mechanical flexibility and easy fabrication with friendly environment. The single bulk heterojunction(BHJ) PSCs based on the PFFBT4T-2OD polymer has achieved a PCE(power conversion efficiency) of 10.8%, in which this D-A type copolymer consists of the donor unit of thiophene and the acceptor unit of 5,6-difluorobenzo[c][1,2,5] thiadiazole. However, PSCs still have not been realized commercial application. In order to improve photovoltaic performance of PSCs, several methods have been adopt –ed, including the design of high-efficiency organic materials, interface modification, morphology control of blend films and optimization of device structure. Among these improved methods, the morphology control of active layer using solvent additives is a relatively simple and efficient way to enhance the efficiency of PSCs. In the paper, three benzene derivatives were first used as solvent additives, their effect on the photovoltaic performance of PSCs and the related mechanisms were mainly investigated. By changing the functional groups on the benzene ring, the device per formance was improved gradually. The main contents and results were as follows:Firstly, benzyl acetate(BA) was used as the solvent additive, which is organic compound without any halogen or sulphur atoms. The PSCs using P3 HT as the donor, PC61 BM as the acceptor and chlorobenzene(CB) as solvent were fabricated at different concentrations of the BA additive from 1.0%, 2.0% to 3.0%, respectively. The effect of the BA concentrations on photovoltaic performance of PSCs was investigated. The results show that the P3HT/PC61BM-based PSCs at a 2% doping concentration exhibited a PC E of 3.85% without any thermal treatment. By some analyses of Hansen solubility parameters(HSPs), ultraviolet-visible absorption spectra(UV-vis), X-ray diffraction(XRD) plot, atomic force microscopy(AFM) plot, current characteristics of the PSCs, the intrinsic acting reasons of the BA additive on device performance were studied elaborately.Secondly, 1,2,4-trichlorobenzene(TCB) was used as the solvent additive. The PSCs using P3HT:PC61BM(1:1) as the active layer and C B as solvent were fabricated at different doping concentrations of the TC B additive from 1.0%, 2.0%, 3.0% to 4%, respectively. The effect of TC B concentrations on photovoltaic performance of PSCs was investigated. The results show that the photovoltaic performance of the P3HT/ PC61BM-based PSCs was significantly improved by adding the TCB additive into the blend without annealing. The PC E values first increased, then decreased with the increasing additive ratios from 1% to 4%. At a 3% doping concentration, the P3HT/ PC61BM-based PSCs exhibited a PCE of 4.17% without any thermal treatment and an increased PC E 4.74% with a FF value of 0.74 after annealing. The FF value is the highest value reported among the P3HT:PC61BM system.Thirdly, ethyl benzoate(EB) was used as solvent additive. The PSCs using P3HT: PCBM(1:1) as the active layer and CB as solvent were fabricated at different doping concentrations of the EB additive from 1.0%, 2.0% to 3.0%, respectively. The effect of the EB solvent additive on photovoltaic performance of polymer photovoltaic device and their related mechanism were studied. The P3HT:PCBM-based PSCs exhibited better photovoltaic performance by device optimization. The PSCs based on P3HT:PC71BM displayed an increased PCE of 4.56%, while the devices based on P3HT:PC61BM displayed a PCE of 4.27% at a 2.0% doping concentration without any thermal treatment. With further annealing treatment, the P3HT:PC71BM-based PSCs exhibited further increased PCE of 5.26% with the fill factor of 0.72. This PCE value is currently one of the highest efficiency in the P3HT:PC BM-based PSCs. |
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