The Control Of Organic Photovoltaic Active Layer Morphology And Charge Transfer Performance

Recent decades,polymer solar cells?PSCs?have attracted lots of research attention due to their light-weight,solution processing,low-cost,and large-area products.In this thesis,three small molecular acceptors?ITIC-SC6,ITIC-SC8 and ITIC-SC2C6?were synthesized and the influence of side chains on their performances in solar cells was systematically probed.In addition,in order to improve the performance of PSCs by expanding the absorption scope of the active layer of devices,a series of ternary blend PSCs were fabricated and systematically investigated.The main results are as follows:1.Non-Fullerene Acceptors?NFAs?have their own advantages over fullerenes acceptors in organic solar cells.NFA molecules comprise a planar backbone and out-of-plane side chains.The former can form effective interchain?-?overlaps and enhance intermolecular charge transport;while the latter can supply the solubility and restrict the strong self-aggregation of molecules.We synthesized three kinds of NFAs,ITIC-SC6,ITIC-SC8 and ITIC-SC2C6,fabricated corresponding solar cells and tested.The results have demonstrated that the variation of side chain greatly affect the charge dissociation,charge mobilities and morphology of the donor:acceptor blend films.Among them,ITIC-SC2C6 with four branched side chains showed good solubility,which can ensure the polymer donor to form favorable fibrous nanostructure during the drying of the blend film.Devices based on PBDB-ST:ITIC-SC2C6 demonstrated higher charge mobility,more effective exciton dissociation,and power conversion efficiency of 9.16%with a J_scc of 15.81 m A cm^-2,a Voc of 0.92 V,and an FF of 0.63These results indicate that side-chain engineering is an effective way of tuning the morphology of blends and Improving the photoelectric conversion efficiency of polymer solar cells.2.In order to improvethe film morphology of active layer in PSCs.phenyl-C₇₁-butyric acid methyl ester(PC₇₁BM)was introduced as the third component due to its good electron-transporting ability and weak crystallinity.A fused pentacyclic electron acceptor?IDT-2O?with four alkyl side chains attached to the planar core,which compound displays a strong crystallinity.If the large aggregation of this compound can be suppressed,well nanoscale phase separation can be achieved,a good photovoltaic performance can be expected since the closely packed molecules is beneficial to charge transport.As a result,the optimal ternary blend device with the ratio of PBDB-T:IDT-2O:PC₇₁BM of 1:0.8:0.2 shows more high and balanced hole/electron mobilities,these values are 2.21×10^-44 cm²V^-1s^-1/and 1.79×10^-44 cm²V^-1s^-1,repectively.A maximum PCE of 10.67%has been obtained for this kind of ternary device,which is the highest reported value for single active layer PSCs mainly based on few-cyclic?<7 rings?electron acceptor without any additive and annealing treatment.