How to Construct Efficient Planar Inverted Aqueous-Based Perovskite Solar Cells Using NiOx Hole Transport Layers?

Perovskite solar cells (PSCs) fabricated by using conventional organic solvents face severe toxicity and environmental challenges. Aqueous processing will offer a promising green alternative. The regular aqueous-based PSCs (A-PSCs) have demonstrated photovoltaic performance comparable to that of their organic solvent-based counterparts. Nevertheless, the planar inverted A-PSCs (PIA–PSCs) exhibit substantially inferior performance or even failure when using nickel oxide (NiOx) as a hole transport layer. One of the reasons is that the “island-like” growth of lead nitrate (Pb(NO3)2) crystals on the NiOx substrates is due to their mismatched physicochemical properties, which ultimately results in a perovskite film with a discontinuous morphology. Thus, we investigate the influence of temperature-modulated (TeMo) NiOx substrates on Pb(NO3)2 crystallization and reveal that the surface free energy and surface potential distribution of substrates critically govern precursor solution wettability and crystallization kinetics. Through TeMo, high-quality aqueous-based Pb(NO3)2 precursor films and then perovskite films were finally achieved. The satisfactory PIA–PSC achieved a champion efficiency of 18.34%, which is among the highest reported for PIA–PSCs. Besides, unencapsulated devices also demonstrated excellent thermal and environmental stability. This work provides a novel and practical approach to develop high-performance, eco-friendly planar inverted aqueous-based PSCs.