Anchoring Formamidinium Hypophosphite in Formamidinium Iodide Enabling Impressive Crystallization Quality for Wide‐bandgap Perovskite Films

Abstract The severe open‐circuit voltage ( V OC ) loss arising from poor crystallization quality of absorbers is a considerable challenge in the wide‐bandgap (WBG) perovskite solar cells (PSCs), impeding the lift of power conversion efficiency (PCE). The traditional methods of introducing additives to improve the quality of absorbers are generally carried out during the fabrication process of PSCs, which increases the complexity of the fabrication process and raises the manufacturing costs. In this context, a new complex called formamidinium hypophosphite (FAHP) is synchronously synthesized during the crucial raw material synthesis of formamidinium iodide (FAI). This FAHP is found to facilitate perovskite crystallization. The trace amount of FAHP tends to coordinate with Pb 2+ in the perovskite precursor solution, and the formed complex decomposes, leading to the delay of crystallization rate during the annealing process of perovskite films, thus enabling the WBG perovskite films with respectable crystallinity and minor detrimental defects. The corresponding champion PSC displays a remarkable PCE of 23.26% with V OC of 1.26 V. In addition, the unencapsulated devices maintain more than 80% of their initial PCE after 1400 h storage in air.