Side-chain tailoring of benzodithiophene derivatives as hole-transporting materials for stable perovskite solar cells

The high cost of Spiro-OMeTAD and the poor stability of devices remain a critical challenge for commercialization of perovskite solar cells (PSCs). Hence, the development of efficient hole-transporting materials (HTMs) seems imperative. Herein, three alkyls-modified HTMs named BTPA-C, BTPA-3C and BTPA-8C were designed and synthesized. Through tailoring their alkyl side-chain length, the structure-property relationships such as photophysical, electrochemical properties and the photovoltaic performance of corresponding PSCs were systematically investigated. Results demonstrate that the HTMs exhibit similar energy level, absorption and emission spectra. However, through tailoring their alkyl side-chain length, the film-forming and hole-transporting ability of HTMs can be greatly affected. Compared to BTPA-C or BTPA-8C, BTPA-3C with a moderate side chain length was endowed with the highest PCE of 18.60%, which was even comparable to that of PSCs based on Spiro-OMeTAD. Meanwhile, compared to the latter, PSCs based on BTPA-3C exhibited significantly improved stability at a relative humidity of 45 ± 5%, maintaining more than 80% of the initial efficiency after aging for 30 days. •Three new hole-transporting materials based on benzodithiophene were synthesized, characterized and investigated.•Various length of side-chains were introduced into materials to optimize the film-forming and carrier-transferring ability.•The hydrophobicity of hole-transporting materials partly determined humidity stability of perovskite solar cells.