Influence of annealing temperature of nickel oxide as hole transport layer applied for inverted perovskite solar cells

Nickel oxide (NiO) has recently attracted great attention for its use as a hole transport layer (HTL) of inverted perovskite solar cells (PSCs). In this paper, NiO films are fabricated on a silicon wafer and fluorine-doped tin oxide by plasma-enhanced atomic layer deposition (PEALD) with nickelocene as the metal precursor and oxygen plasma as the coreactant. The effects of the annealing treatment on the film properties at different annealing temperatures are analyzed. The experimental results show that the PEALD-NiO films have a high thickness uniformity and low surface roughness as evaluated by atomic force microscopy measurements. All the PEALD-NiO films have a wide bandgap and high transmittance of ∼80%–85% in the visible light range. The postannealing treatment induces a reduced electrical resistivity owing to crystal structure repair and surface defect reduction. This treatment also leads to a significantly enhanced wettability of the NiO films, facilitating perovskite layer deposition in subsequent device fabrication. Finally, the inverted PSCs based on the NiO HTL with different annealing temperatures demonstrate an enhanced performance of the device as compared to that with unannealed NiO HTL. The 400 °C-annealed PEALD-NiO HTL yields the best cell conversion efficiency, improving from 15.38% for unannealed NiO to 17.31%, demonstrating the potential of PEALD-NiO compact films for applications in inverted PSCs.