Additives with Urethane Functional Group for High Stability and Flexibility of Perovskite Solar Cells

Abstract

Organic-inorganic mixed halide perovskite solar cells (PeSCs) have recently studied in photovoltaic field due to their many advantages such as low cost, high absorption coefficient, long exciton diffusion length, and high carrier mobility. According to the NREL chart, the efficiency of the PeSCs has been renewed to 25.2 % this year in 2019. The progress of PeSCs is significantly attributed to the efforts in the solvent engineering, interface modification, and compositional tuning. However, instability of PeSCs is a critical hindrance to the commercialization, because the lead halide perovskite materials are very sensitive to humidity leading to rapid degradation of power conversion efficiency. In recent, there are several ways of getting high stability via encapsulation, adding hydrophobic layers, developing new materials, and introducing additives. In this work, we adopted a simple way for enhancing stability of PeSCs by introducing two additives with same functional groups of urethane to the perovskite precursor solution: ethyl N phenylcarbamate (EP) as a small molecule and polyurethane (PU) as a polymer additive. The PeSCs with additives exhibited high power conversion efficiency of 20% (EP) and 18.7% (PU) respectively, with excellent stability under high humidity condition. Furthermore, we fabricated flexible devices and confirmed that additives with urethane functional group effectively enhance the flexibility of PeSCs through the bending test. Among two additives, EP showed better device performance and moisture stability than PU, which seemed more suitable as an additive.