Functionalization of Donor--Acceptor Hole Transport Materials Enhances Crystallization and Defect Passivation in Inverted Perovskite Solar Cells: Achieving Power Conversion Efficiency >21% (Area: 1.96 cm²) and Impressive Stability

Inverted perovskite solar cells (PSCs) mainly adopt polytriarylamine (PTAA) for the hole transport material (HTM), which usually brings about inferior interfacial contact owing to their hydrophobicity, high-lying highest occupied molecular orbital energy level, and deficiency of passivation groups. Herein, a series of donor-pi-acceptor (D-pi-A) type small molecules is demonstrated based on 2,2 ':6 ',2 ''-terpyridine (TPy) as the acceptor moiety, benzene ring as the pi-linker, and incorporating various donors to act as HTMs. These TPy-based molecules coated atop PTAA manipulate the energy level and surface wettability, but the incorporation of the phenoxazine (POZ) donor can be prominent for enhancing charge transport and defect passivation, thereby simultaneously addressing the above-mentioned issues. The highest power conversion efficiency of 22.36% can be achieved with an open-circuit voltage (V-OC) of 1.15 V, a short-circuit current density (J(SC)) of 23.96 mA cm(-2), and a fill factor (FF) of 81.16% for the optimized POZ-TPy-modified device. Moreover, the power PCE of a large POZ-TPy-modified device (1.96 cm(2)) can still reach more than 21%. These results are among one of the highest efficiencies for inverted PSCs, indicating the enormous potential of POZ-TPy HTM in future perovskite applications.