Synthesis And Characterization Of Organic Solar Cell Acceptor Materials Based On Isoindigo Derivatives

With the rapid development of the economy and the continuous advancement of science and technology,environmental pollution and energy depletion have become increasingly serious.In order to solve this problem,it is extremely urgent to develop new pollution-free green energy.As a source of a wide range of green energy,solar energy is receiving more and more attention.As a device that can effectively convert solar energy into electrical energy,organic solar cells have been widely used and developed due to their advantages of relatively light weight,relatively low cost,and large-area preparation.The active layer of the organic solar cell is composed of a blend of the donor material and the acceptor material.At the early stage,the most widely used acceptor material is the fullerene material.However,the tedious purification process,limited absorption in visible region and the untunable energy levels of the fullerene significantly suppressed the further development of OSCs.Therefore,it is very essential to synthesize novel non-fullerene aeceptors for their low cost and finely tunable absorption range and energy levels.In this work,six kinds of isoindigo-based polymer acceptors were designed and synthesized,and the optical,electrochemical,and electron mobility properties were characterized.Finally,the all-polymer solar cells were fabricated based on the terpolymer acceptors and the relationship between the molecular structures and photovoltaic performance was also revealed.The specific works are as follows:1.The terpolymer acceptors,PIID-BO/HD-T and 2Cl-PIID-BO/HD-T,based on isoindigo,chlorinated isoindigo and thiophene were designed and synthesized.In order to study the influence of the chlorine atoms,their UV-visible absorption,thermal stability and electrochemical properties were measured.The results showed that the introduction of the chlorine atoms into the acceptors could effectively adjust the optical properties and the aggregation behaviors of the polymer.For example,the chlorinated polymer,2Cl-PIID-BO/HD-T,exhibited significantly broadened absorption spectrum and weakened aggregation behavior.Using J52-2Cl as the donor material,the all-polymer solar cells based on J52-2Cl:PIID-BO/HD-T and J52:2Cl-PIID-BO/HD-T were prepared,respectively,and the device based J52-2Cl:PIID-BO/HD-T exhibited superior performance than that of J52:PIID-BO/HD-T.The possible reason is that the chlorinated polymer has weak crystallinity due to the weakening of aggregation behavior and a better orientation is used when blending with the donor,at the same time,the lower LUMO energy level of the chlorinated polymer（2Cl-PIID-BO/HD-T）increases the driving force and accelerates the dissociation of the excitons,so the performance of device is improved.2.Considering the large influence of aggregation behavior on the molecular properties,three kinds of monomers based on the modified isoindigo molecules were designed and synthesized by changing the length of alkyl side chains and the introduction of chlorine atoms.Four kinds of polymer acceptors with different degrees of conjugation,PIID-C₂₀-T,PIID-C₂₀-Cl-T,PIID-C₈/C₂₀-T and PIID-C₈/C₂₀-Cl-T,were synthesized by Stille polymerization.The optical properties,electrochemical properties and mobility of the four acceptors were characterized to explore the relationship between the molecular structure and polymer properties.The results displayed that the electron mobility of the ternary copolymer synthesized by introducing a chlorine atom-incorporated polymer(PIID-C₂₀-Cl-T and PIID-C₈/C₂₀-Cl-T)and increasing the degree of conjugate of the polymer in the isoindigo is markedly improved.And the electron mobility of the polymers after chlorination are relatively stable in air.The results show that introduction of chlorine atoms and the degree of conjugation of the polymers can effectively adjust the performance of the electron acceptors based on the isoindigo derivative.