Unveiling the Role of Conjugate Bridge in Triphenylamine Hole-Transporting Materials for Inverted and Direct Perovskite Solar Cells

Deeply understanding of the performance discrepancy of hole-transporting materials (HTMs) in perovskite solar cells (PSCs) with different configuration (inverted or direct) is important for designing efficient HTMs. Herein, three organic HTMs TZ1, TZ2, and TZ3 have been employed to fabricate the inverted PSCs. Optoelectronic properties and photovoltaic performance of these HTMs are investigated. TZ3 featuring the 3,6-di(thiophen-2-yl)thieno[3,2-b]thiophene conjugate bridge shows a higher work function and enhanced capability of hole extraction, achieving a higher power conversion efficiency (PCE) of 16.33% in the inverted PSCs. Importantly, results reveal that the conjugate bridge has a relevant effect on the photovoltaic performance of cells with different device configuration. The PCE trend of TZ1, TZ2, and TZ3 in inverted PSCs is diametrically opposed to that of direct devices. We proposed that linear triphenylamine HTMs contain a fused bridge with high degree of conjugation are good choice for the direct PSCs. On the other hand, it is better to incorporate linear triphenylamine HTMs with deep highest occupied molecular orbital (HOMO) toward the inverted PSCs, because the photovoltage plays a crucial role in the efficiency of the inverted PSCs. This systematic study provides a new viewpoint to design HTMs toward PSCs with different device configuration.