Ammonia-treated graphene oxide and PEDOT:PSS as hole transport layer for high-performance perovskite solar cells with enhanced stability

Poly(3,4-ethenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and graphene oxide (GO) as well as their hybrids have been widely used to prepare hole-transport layer (HTL) for inverted planar perovskite solar cells (PeSCs). However, their acidic nature is detrimental to the stability of PeSC. In this study, we report a simple and general strategy to prepare non-corrosive HTL by treating GO and PEDOT:PSS with ammonia or ammonium (i.e., (NH4)2HPO4), respectively. The PeSC based on ammonia-treated GO (a-GO) yields a power conversion efficiency (PCE) over 14%, remarkably outperforming those with pristine GO (∼12%) or PEDOT:PSS (∼13%). Similar improvement is also observed for the devices with ammonia or ammonium-treated PEDOT:PSS. The mechanism behind such improvement is thoroughly studied, demonstrating the significance of ammonia treatment on the HTL performance. More importantly, the devices based on ammonia-treated HTL exhibit significantly improved stability, as compared to those based on pristine PEDOT:PSS and GO.