Effect of heterocyclic spacer on property of hole-transporting materials with silafluorene core for perovskite solar cells

Three hole-transporting molecules S-O, S-S and S-Se are designed through introducing heterocyclic spacers into the silafluorene core of S101. The effects of heterocyclic spacer on the geometry, electronic property and hole mobility of these materials are investigated systematically through using the DFT, Marcus formula and Einstein relation. The HOMO energy levels of S-O, S-S and S-Se are lower than that of S101 from calculated results, indicating that introduction of heterocyclic spacer can improve the open circuit voltage of device. Further, all of the designed molecules with heterocyclic spacer have larger electronic coupling relative to S101 because of more efficient intermolecular pi-pi stacking and interactions, which makes their hole mobility be higher than that of S101. The hole mobility will decrease gradually with the increase of heteroatom number. That is, the way introducing heterocyclic spacer into the silafluorene core of hole-transporting materials can enhance the hole transfer ability. The present theoretical investigation provides a meaningful way for improving the hole transport property of silafluorene-based materials.