Synthesis And Photovoltaic Performance Of Non-fullerene Small-molecule Acceptor Materials

Organic solar cells?OSCs?have become more and more competitive,due to their advantages such as light weight,easy preparation,and low cost.In recent years,thanks to the rapid development of non-fullerene small-molecule acceptor materials,the power conversion efficiencies?PCEs?of organic solar cells have increased rapidly.Currently,the efficiency of photovoltaic devices prepared in laboratories has exceeded18%,showing great application prospects.Compared with traditional fullerenes acceptors and their derivatives,non-fullerene small-molecule acceptors have the advantages of easy modification of chemical structures,wide spectral absorption range,simpler synthesis and purification,and no batch differences.Small-molecule acceptors are still the driving force for the development of organic photovoltaics.The spirodifluorene unit has a rigid,three-dimensional spatial structure,which is conducive to the construction of amorphous organic semiconductor materials.In this dissertation,a series of non-fullerene small-molecule acceptor materials are designed and synthesized with spirodifluorene as the core,and the influence of molecular structure on the electrochemical,optical,thermal,and photovoltaic devices of materials is studied.At the beginning,we synthesized two small-molecule acceptor materials SPIC and SPCl based on the spirodifluorene.The difference between the two lie in the Cl substitution on the end groups 3-?dicyanomethylene?inden-1-one.Both materials are easy to synthesize and purify,and have high thermal stability.In the thermogravimetric analysis?TGA?test,the decomposition temperatures are 346.2°C and 331.8°C,respectively.Differential scanningtest shows that both are amorphous.Electrochemical tests found that the introduction of the Cl atoms enhanced the electron-withdrawing ability of the end groups and deepened the lowest unoccupied molecular orbital?LUMO?energy level.The power conversion efficiency of photovoltaic devices with the PTB7-Th as the donor?ITO/Zn O/PTB7-Th:acceptor/Mo O₃/Al?is 1.17%and 1%,respectively.Then,we introduced cyclopentadithiophene as a bridge to increase absorption of the molecule,and designed and synthesized C8DT and C8DT-Cl.Both materials are simple to synthesize,and the target products can be recrystallized to obtain analytically pure samples.Compared to SPIC and SPCl,the maximum absorption peaks of C8DT and C8DT-Cl in solid state are also red-shifted by about 100nm,respectively 679nm and 694nm.Therefore,we selected PBDB-T that is a complementary wide band gap polymer as the donor material.Based on C8DT and C8DT-Cl,power conversion efficiencies of 7.25%and 8.03%were obtained in organic photovoltaic devices?ITO/Zn O/PBDB-T:acceptor/Mo O₃/Al?,respectively.