New 3D-structure Perylene Diimide Electron Acceptors With Triptycene Core For Organic Solar Cells

Perylene diimide(PDI),known as a classical n-type organic semiconductor material,had been proved to be a good acceptor material in organic solar cells(OSCs).In this thesis,to extend development of three-dimensional(3D)PDI small molecular(SM)acceptors,we designed a series of PDI-based acceptors with the triptycene core.Their photoelectric properties were investigated in terms of theoretical simulation and experimental synthesis methods.The influences arising from “the heteroatom-substituted bridge-carbon of triptycene”and “the connection style between PDI units and triptycene core” were first studied by the theoretical calculation method.The results showed that the heteroatom-substitution had a negligible effect on the energy levels of the acceptor materials,but it could increase the twist angles between the triptycene and PDI units,which was not conducive to the intramolecular charge transfer.As for effect of the connection mode,the TP3 acceptor,with the bay-position of PDI units connected to triptycene,had a broad sunlight absorption area and suitable energy levels matching with donor material PTB7-Th.The TPDI-3 acceptor,with the N-position of PDI units connected to triptycene,had a strong sunlight absorption and large charge transfer matrix element.Therefore,TP3 and TPDI-3 could act as the potential high-efficiency small molecular PDI-based acceptors.TPn(n=1,2,3)acceptors were synthesized by Suzuki coupling reaction,and had a good solubility and thermal stability.With increase of PDI units,the acceptor materials showed a gradually enhanced absorption spectra,but no significant changes in the electron energy levels and the absorption areas.The OSCs was fabricated with a PTB7-Th:TP3blend film as the active layer and showed the best power conversion efficiency(PCE)of3.16%.The rough film surface led to the low filling factor,which was the main reason for the poor performance of the OSCs.TPDI-n(n=1,2,3)acceptor materials were synthesized in which the N-position of PDI units were connected with triptycene core.Increasing number of PDI units only improved the absorption ability of the TPDI-n acceptors.Further research on thephotovoltaic devices based on TPDI-3 acceptor are ongoing.The PTB7-Th/TPDI-3blending film showed a smooth and uniform morphology,which would lead to a higher fill factor and the electron transfer rate in OSCs.Based on the results of the above theoretical calculation and photoelectric experiment,we designed three acceptors TPCH,TPS and TPSe.The thiophene or selenophen unit with the electron donating ability was built in TPS or TPSe acceptor when the S or Se atoms were introduced in the PDI units,leading to the larger ? planes.The LUMO levels of the acceptors had not obviously changed,but the HOMO energy level decreased and resulted in the wider band gaps.Compared to TPCH and TPS,the TPSe showed an obvious red shift in the sunlight absorption area and had a satisfactory charge transfer matrix element.So,we reasonably believe that TPSe could be a promising electron acceptor for high-efficiency OSCs.