Positional effect of triphenylamine group on optical and charge transfer properties with thiophene-based hole transporting materials.

Hybrid organic-inorganic perovskite solar cells (PSCs) have shown significant potential for use in the energy field. Typically, hole-transporting materials (HTMs) play an important role in effecting the power conversion efficiency (PCE) of PSCs. A deep understanding of the structure-property relationship plays a vital role in developing efficient HTMs. Herein, the relationship between the structure and properties of two small organic HTMs H2,5 and H3,4 were systematically investigated from the respects of the electronic and optical properties, and the hole-transporting behavior by using density functional theory (DFT) and Marcus electron transfer theory. Results demonstrated that the high power conversion efficiency of based H2,5 PSC was caused by strong interactions with perovskite material on interface and enhanced hole mobility in H2,5 compared with H3,4 . The strong interaction devises form the short bond length of O atom of HTM and Pb atom of perovskite material, and the highly hole mobility derives from the quasi-planar conjugated conformation and tight packing model of neighboring molecules in H2,5 . Besides, we also find that the planar structure enhances the intermolecular interaction between HTM and perovskite materials compared with the 'V' shaped molecule. Importantly, we also note that the HOMO level of the isolated molecule is not always proportional to the open-circuit voltages of PSCs since the HOMO level might move toward a higher level when the interaction between HTM and interface of perovskite was included. The work gives essential information for rational designing efficient HTM.