Application of Single-molecule Liquid Crystal Additives in CH(NH2)2PbI3 Perovskite Solar Cells

Solution-processed perovskite films usually contain a large quantity of grain boundaries, which decrease the film crystalline quality and introduce severe defect recombination, hindering performance of the devices based on them. Therefore, preparation of high-quality films to achieve high power conversion efficiencies remains a great challenge for perovskite solar cells. Due to high abilities of self-assembly and morphology-tuning for liquid crystal molecules, a single-molecule liquid crystal 4-cyano-4'-pentyl biphenyl (5CB) was employed as additive in CH(NH2)(2)PbI3 ( FAPbI(3)) precursor solution to increase the perovskite grain size and decrease the grain boundaries. In addition, the cyano group in 5CB passivates the uncoordinated Pb2+ in the perovskite films, which reduces the trap density concentration and inhibits the nonradiative recombination. The resulting perovskite solar cells with 0.2 mg/mL 5CB in the precursor achieve an efficient power conversion efficiency of 21.27% with an open circuit voltage of 1.086 V, a current density of 24.17 mA/cm(2), and a fill factor of 80.96%. In conclusion, introducing single-molecule liquid crystal as additive is a facile and efficient strategy for improving the performance of FAPbI(3) solar cells.