Construction of Efficient Cs₂AgBiBr₆ Perovskite Solar Cells by Enhancing Hole-Selective Contact with Deep-Level Dopant-Free Hole Transport Material

The mismatched energy level alignment at the hole transport interface is recognized to be a prominent limitation for the Cs2AgBiBr6-based perovskite solar cell (PSC) to achieve high power conversion efficiency (PCE) but has not been well investigated yet. In order to solve this problem to some extent, it is proposed to balance the energy offset at the Cs2AgBiBr6 and hole transport material (HTM) interface to reduce the hole transport barriers, and a novel HTM TPTI-TPA2F with deep level is designed to implement this strategy. The research demonstrates that, on the one hand, the planar pi-conjugation and the presence of multiple heteroatoms on TPTI-TPA2F facilitate the formation of well-oriented film and surface defect passivation; on the other hand, the higher film ionization potential of TPTI-TPA2F effectively balances the energy barrier for hole transport. As a result, improved hole-selective contact is achieved with TPTI-TPA2F as HTM, and the interfacial energy loss is suppressed. Correspondingly, the optimized Cs2AgBiBr6 PSCs using the TPTI-TPA2F HTM without doped feature an excellent PCE of 4.05% and a high open circuit voltage of 1.15 V, with much improved long-term humidity and thermal stability. This work provides an attractive strategy for developing efficient Cs2AgBiBr6 PSCs.