Efficient additive-free FAPbI3 perovskite solar cells achieved by promoting homogeneity

Abstract

Formamidinium lead iodide (FAPbI₃) has received substantial research interest for photovoltaic applications due to its excellent thermal stability and narrow bandgap close to the Shockley–Queisser limit. Unfortunately, the compositionally pure FAPbI₃-based perovskite solar cells (PSCs) have unsatisfactory efficiency and the common approach of incorporating additives into FAPbI₃ has been used to improve their properties. However, commonly used additives generally contribute to the complexity of the FAPbI₃ composition, which could pose potential risks to the long-term operational stability of PSCs. Here, we report a strategy for the fabrication of additive-free FAPbI₃ films using a low pressure assisted (LPA) method. By adjusting the pressure reduction rate, we achieved compositionally pure FAPbI₃-based PSCs with power conversion efficiency (PCE) exceeding 20%, along with enhanced thermal stability and long-term stability under working conditions. The improved optoelectronic properties can be attributed to the excellent homogeneity of the FAPbI₃ film with low defect density and better carrier extraction at the interface between the FAPbI₃ film and carrier-transport layers. This further leads to better thermal and long-term operational stability of the FAPbI₃ PSCs.