Improving the Optoelectrical Properties of a Nickel Oxide Hole Transport Layer by Hydrogen Peroxide Treatment for Efficient Organic Solar Cells

Nickel oxide (NiO x ) is one of the promising hole transport materials (HTMs) for organic solar cells (OSCs) due to its negligible parasitic absorbance, good chemical stability, and large band gap compared to the conventional organic HTMs. The preparation of the NiO x thin film through a combustion method offers the advantages of simplicity and low processing temperatures. However, the inherent limitations of NiO x, such as its low conductivity and high trap density, hinder its performance. Here, a solution treatment using hydrogen peroxide (H 2 O 2 ) has been introduced to NiO x films to improve their electrical properties. The H 2 O 2 treatment significantly facilitated Ni 3+ formation, resulting in a deeper work function and valence band maximum of NiO x, which was confirmed by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. OSCs incorporating the H 2 O 2 -treated NiO x with a PM6:Y6 active layer have achieved a maximum power conversion efficiency (PCE) of 15.81% and an open-circuit voltage ( V oc ) of 0.827 V, surpassing the performance of control NiO x -based OSCs. Furthermore, NiO x -based devices exhibited drastically enhanced stability in comparison to the PEDOT:PSS-based devices under a 65 °C/85RH% condition. This work proposes an effective strategy for improving the electrical properties of NiO x HTMs synthesized by the combustion method, thereby advancing the development of more efficient and stable OSCs.