Regulation Of Photovoltaic Performance Of All Polymer Solar Cells Acceptor By Random Copolymerization

All-polymer solar cells(APSC)have been widely reported for their unparalleled properties such as excellent tunability of optical and electronic properties,outstanding mechanical flexibility,and good device stability due to its active layer materials are all composed of polymeric materials.Currently,the development and design of efficient polymeric acceptor materials is the core way to facilitate the rapid development of APSC.In this paper,a series of novel polymer acceptor materials are designed and synthesized by using the method of ternary random copolymerization,aiming at the shortcomings of current high-efficiency polymer acceptor materials.At the same time,the regulation of random copolymerization on polymer performance and its influence on the optimization of photovoltaic devices are also explored.First of all,we designed and synthesized a series of new random copolymers,PNDI-Px,by introducing porphyrin units with excellent light-absorbing into naphthalenediimide(NDI)-based acceptors through random polymerization,with the aim of solving the problems of low light-absorbing coefficient and strong crystallinity of the current NDI-based polymer acceptors.Through the introduction of porphyrin units,we synergistically modulate the absorbance intensity and crystallinity of the polymeric acceptors.It was found that with proper porphyrin unit loading,the new random polymer acceptors have higher absorption coefficients,higher lowest unoccupied molecular orbital(LUMO)energy levels,more flexible backbones and lower aggregation.As a result,the photovoltaic parameters of all-polymer solar cells prepared by pairing the polymer acceptor PNDI-P10 with PBDB-T donor were all significantly improved with PCE of 5.93%,J_SC of 12.84 m A cm^-2,V_OC of 0.85 V and FF of 54.34%.Secondly,polymerized small molecule acceptor(PSMA)based on small molecule polymerization is difficult to obtain the best morphology in the blend film due to the highly rigid fused ring with large planar or quasi-plane,so we introduced3-(2-(2-ethoxyethoxy)ethoxy)thiophene(ET)unit as the third unit into the high-performance D-A type copolymer PYT,obtaining a series of new random copolymers,PYT-ET(x).It was found that the introduction of electron-rich units containing alkoxy chains not only elevated the LUMO energy level of the polymer,but also modulated the polymer co-mixing morphology,resulting in a more suitable phase separation size between the donor acceptors,which is favorable for exciton dissociation and charge separation,thus contributing to the improvement of the overall photovoltaic parameters of the device.Finally,the optimal efficiency of the reference PBDB-T:PYT device is 11.75%,while the device based on PBDB-T:PYT-ET(10)achieves a PCE of 12.77%.