Efficient Perovskite Solar Cells Enabled by Co-Depositable p-Type Small Molecules
Metal halide perovskites have significantly improved solar cell performance due to their excellent optoelectronic properties. Recently, p-type small molecules such as Me-4PACz, assisted by dual-functional passivation, have enabled perovskite solar cells (PSCs) to achieve certified power conversion efficiencies (PCEs) up to 26.15%. However, issues such as molecular aggregation during solution processing limit the storage stability of precursor solutions and lead to poor molecular distribution within the film, hindering device efficiency and operational stability. Zhu's group enacted the co-deposition of a new p-type small molecule, D4PA, with perovskite. Density functional theory (DFT) investigations revealed that D4PA exhibits strong dual-terminal anchoring interactions with indium tin oxide (ITO) via two phosphonic acid groups, stabilized by intramolecular hydrogen bonding, ensuring robust adhesion and improved interface uniformity. Additionally, D4PA forms stable coordination with Pb2+ ions, suppressing defects and facilitating efficient charge transfer. Temperature-dependent Fourier-transform infrared (FTIR) spectroscopy confirmed strong binding between D4PA and perovskite, contrasting with the weaker binding of Me-4PACz. This stable interaction improves perovskite crystallinity and promotes uniform distribution of D4PA, resulting in superior photovoltaic performance. D4PA-based PSCs achieved a record PCE of 26.83% in small-area devices (certified 26.72%), and a mini-module (10.86 cm2) achieved a PCE of 23.37% with a certified MPPT efficiency of 22.66%. Devices retained 97.2% of initial efficiency after 2500 h of continuous operation at MPP under one-sun illumination. Reduced and homogeneous photoluminescence intensity indicated efficient and uniform hole extraction, and electroluminescence quantum efficiency (EQE-EL) reached 15.25%, significantly higher than 6.23% for Me-4PACz-based devices. This molecular engineering strategy provides a promising route for high-performance and high-durability inverted PSCs.