Formamidine lead iodide (FAPbI3 ) is the best absorber material in perovskite solar cells (PSCs), while the application of FAPbI3 in inverted structure PSCs has not been successful, mainly due to its hydrophobic or defective Film formation on hole transport substrates is poor.
Here, Wu Yongzhen et al. of East China University of Science and Technology report substantial improvements in inverted PSCs based on FAPbI3 via a multifunctional amphipathic molecular hole transporter (2-(4-(10H-phenothiazine- 10-yl)phenyl)-1-cyanovinyl)phosphonic acid (PTZ-CPA). Phenothiazine (PTZ)-based PTZ-CPA carries cyanovinylphosphonic acid (CPA) groups, forming a superwetting hole-selective bottom layer that can easily deposit high-quality FAPbI3 films.
Compared with the previously established carbazole-based hole-selective material (2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl)phosphonic acid (MeO-2PACz), PTZ- CPA increases the crystallinity of FAPbI3 and passivates electronic defects more effectively, thereby significantly improving the photoluminescence quantum yield (4 times) and Shockley-Read-Hall lifetime (8 times).
Furthermore, PTZ-CPA shows larger molecular dipole moment and improved energy levels, which is beneficial to interfacial hole collection. Therefore, FAPbI3- based inverted PSCs achieved 25.35% efficiency . The PTZ-CPA based device showed commendable long-term stability, maintaining over 90% of its initial efficiency after 2000 hours of continuous operation at 40°C.
Huidong Zhang, et al, Formamidinium Lead Iodide-Based Inverted Perovskite Solar Cells with Efficiency over 25% Enabled by An Amphiphilic Molecular Hole-Transporter. Angewandte Chemie. 2024