How to Construct Efficient Planar Inverted Aqueous-Based Perovskite Solar Cells Using NiO x 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 (NiO x ) as a hole transport layer. One of the reasons is that the “island-like” growth of lead nitrate (Pb(NO 3 ) 2 ) crystals on the NiO x 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) NiO x substrates on Pb(NO 3 ) 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(NO 3 ) 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.