Reduced Graphene Oxide Improves Moisture and Thermal Stability of Perovskite Solar Cells

Reduced graphene oxide (rGO) is a very stable material with tunable electronic properties dependent on its reduction level. Nevertheless, the incorporation of rGO into perovskite solar cells (PSCs) frequently demonstrates inconsistent results, and it plays an ambiguous role. Here, we systematically explore rGO as an additive in perovskite and 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-MeOTAD) using different reduction levels (O18.42%, O9.67%, and O7.14%). Perovskite with rGO(O9)(.67%) results in the most stable shelf stability, demonstrating a negligible performance degradation over 430 h, while the one without rGO shows a 6.4% drop, mainly due to fill-factor deterioration. Moreover, the improved stability is more pronounced when rGO(O9)(.67%) is employed with spiro-MeOTAD where crystallization is effectively retarded. The integrated effect is also observed in PSCs based on rGO(O)(9.67%) in both perovskite and spiro-MeOTAD, leading to enhanced stability at 85 degrees C and 45% relative humidity.