Thermally Crosslinked Hole Conductor Enables Stable Inverted Perovskite Solar Cells with 23.9% Efficiency.

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) represents the state-of-the-art hole transport material (HTM) in inverted perovskite solar cells (PSCs), however, unsatisfied surface properties of PTAA as well as high energy disorder in the bulk film hinder the further enhancement of device performance. Herein, we strategically develop a simple small molecule 10-(4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)-3,7-bis(4-vinylphenyl)-10H-phenoxazine (MCz-VPOZ) for in-situ crosslinking of polymer hole conductor (CL-MCz) via a facile and low-temperature cross-linking technology. The resulting polymer CL-MCz offers high energy ordering, improved electrical conductivity as well as appropriate energy-level alignment, enabling efficient charge carrier collection in the devices. Meanwhile, CL-MCz synchronously provides satisfied surface wettability and interfacial functionalization, facilitating the formation of high-quality perovskite films with fewer bulk iodine vacancies and suppressed carrier recombination. Significantly, the device with CL-MCz yields a champion power conversion efficiency of 23.9% along with an extremely low energy loss down to 0.41 eV, which represents the highest reported efficiency for non-PTAA based polymer HTMs in inverted PSCs. Furthermore, the corresponding unencapsulated devices exhibited competitive shelf-life stability under various operational stressors up to 2500 hours, reflecting high promises of CL-MCz in the scalable PSC application. This work underscores the promising potential of the cross-linking approach in preparing low-cost, stable and efficient polymer HTMs toward reliable PSCs. This article is protected by copyright. All rights reserved.