Preparation And Photovoltaic Performance Of Polymeric Acceptors Based On Perylene Diimide

The rapid development of human society relies on the exploitation and utilization of energy resources.However,the traditional fossil energies are facing the situation of exhaustion and the environmental pollution caused by its burning process also becomes increasingly prominent.To solve this problem,we urgently need to find renewable clean energy as an alternative to maintain the sustainable development of the future society.And if the solar energy can be effectively developed and utilized,this problem will nolonger be existed.Solar cells can directly convert solar energy into electricity,which is one of the most important ways for the using of solar energy.Organic solar cells show promising prospects due to the advantages of low cost,light weight,flexibility and large-area solution processing.In a bulk hetero-junction solar cell,the light active layer is based on a blend film of an electron-donating material and an electron-accepting material.As for fullerene acceptors,the preparation is costive because of the difficulty in its separation and purification.Fullerene derivatives also shows poor absorption in visible region and it is not easy to modify the energy level and band gap by chemical method.Therefore,it is of great significance to study and develop non-fullerene acceptors to improve the power conversion efficiency(PCE)as well as facilitate the future industrialization of organic solar cells.In this paper,four kinds of polymeric acceptors based on perylene dimide were designed and synthesized.We characterized their optical and electrochemical properties and studied their photovoltaic properties in all polymer solar cells.The specific work is summarized as follows:In the first research system,two novel A-A(acceptor-acceptor)typed polymeric acceptors PPDI-DTBT and PFPDI-DTBT based on perylene diimide/fused perylene diimide and 4,7-Di(2-thienyl)-2,1,3-benzothiodizole were designed and synthesized,and of which the optical properties as well as electrochemical properties were determined.All polymer solar cells based on PPDI-DTBT or PFPDI-DTBT were fabricated using PTB7-Th as donor material.The effects of the concentration ratio of electron donating/electron accepting materials,solvent additives and annealing temperature on the performance of the devices were well studied.Due to the more matched energy levels between PFPDI-DTBT and PTB7-Th as well as the more balanced hole/electron transport performance in the corresponding device,the PFPDI-DTBT device showed more excellent photovoltaic performance.The results indicated that it is an effective strategy to improve the photovoltaic properties of perylene diimide based polymeric acceptor in all polymer solar cells by directly fusing the perylene diimide unit.The efficiency of the PFPDI-DTBT device is as high as 6.23%,which is currently the highest value in such A-A typed polymer acceptors based on perylene diimide.In the second research system,two novel D-A(donor-acceptor)typed polymeric acceptors PFPDI-2T and PFPDI-2FT based on fused perylene diimide and bithiophene/difluoro-substitued bithiophene were designed and synthesized,and of which the optical properties as well as electrochemical properties were characterized.All polymer solar cells based on PFPDI-2T or PFPDI-2FT were fabricated using PTB7-Th as donor material.The effects of the concentration ratio of electron donating/electron accepting materials,solvent additives and annealing temperature on the performance of the device were well studied.The highest power conversion efficiency based on PFPDI-2T and PFPDI-2FT devices was recorded to be 5.35% and 6.39%,respectively.Due to the higher hole and electron mobility in PFPDI-2T device,higher open circuit voltage and short circuit current were obtained,which leading to the higher PCE in PFPDI-2T device.The PCE of the two materials is far higher than the reported polymer based on perylene diimide and bithiophene,which further demonstrated that it is effective to improve the photovoltaic properties of perylene diimide based polymeric acceptor in all polymer solar cell by directly fusing the perylene diimide unit.