Inverted perovskite solar cells with high fill-factors featuring chemical bath deposited mesoporous NiO hole transporting layers

The development of hole transporting layers that optimize charge extraction and minimize interfacial recombination losses offer an important route for further enhancement in the performance of inverted perovskite solar cells (PSCs). NiO is a widely adopted hole transporting material in such devices, possessing a reasonably high hole mobility and suitable energy level positions to provide high efficiency solar cells. However, its use in inverted PSCs has typically resulted in relatively low fill factors, which arises from underlying contact issues between the perovskite and NiO layers. In this work, we address this issue by employing a thin mesoporous NiO scaffold formed via chemical bath deposition as the hole transporting layer. This hole transporting material is found to dramatically improve the performance of inverted mixed cation and anion PSCs by enhancing their light harvesting and charge transporting efficiencies. Optimized devices achieve efficiencies of up to 16.7% and fill factors as high as 85%. These values are significantly higher than PSCs using conventionally spray-deposited planar NiO hole transport layers, which exhibit efficiencies of up to 14.5% and fill factors of only 73%.