Rational design of bis(4-methoxyphenyl)amine-based molecules with different π-bridges as hole-transporting materials for efficient perovskite solar cells

Abstract

Exploration on alternative organic hole-transporting materials (HTMs) especially for high-efficiency perovskite solar cells (PSCs) has attracted great attention recently. In this work, a strategy to tune π-bridged units of the small molecular HTM which consists of bis(4-methoxyphenyl)amine as arm and spiro[fluorene-9,9'-xanthene] as π-bridge were theoretically presented for improvement of the PSC efficiency. The π-bridged tunings could promote the contribution of the highest occupied molecular orbital (HOMO) to delocalize throughout whole molecules in order to be favorable for enhancing the hole transfer integral and hole mobility. Compared with the parent HTM, the new designed HTMs in PSC applications exhibit better performance with higher HOMO energy levels, larger Stokes shifts, little exciton binding energy, better stability and higher hole mobility. Therefore, the strategy on basis of modulating the π-bridge units of small molecules can effectively change the performance of HTMs and thereby provide a useful guideline of π-bridge screening for the design of excellent HTMs in PSC applications. In view of the excellent properties, the designed molecules as HTMs can act as a promising candidates for providing a large efficiency in PSC applications.