Side-chain engineering of high-efficiency conjugated polymer photovoltaic materials

In recent years,conjugated polymers have attracted great attention in the application as photovoltaic donor materials in polymer solar cells(PSCs).Broad absorption,lower-energy bandgap,higher hole mobility,relatively lower HOMO energy levels,and higher solubility are important for the conjugated polymer donor materials to achieve high photovoltaic performance.Side-chain engineering plays a very important role in optimizing the physicochemical properties of the conjugated polymers.In this article,we review recent progress on the side-chain engineering of conjugated polymer donor materials,including the optimization of flexible side-chains for balancing solubility and intermolecular packing(aggregation),electron-withdrawing substituents for lowering HOMO energy levels,and two-dimension(2D)-conjugated polymers with conjugated side-chains for broadening absorption and enhancing hole mobility.After the molecular structural optimization by side-chain engineering,the2D-conjugated polymers based on benzodithiophene units demonstrated the best photovoltaic performance,with powerconversion efficiency higher than 9%.