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

Nickel oxide (NiOx) 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 NiOx thin film through a combustion method offers the advantages of simplicity and low processing temperatures. However, the inherent limitations of NiOx, such as its low conductivity and high trap density, hinder its performance. Here, a solution treatment using hydrogen peroxide (H2O2) has been introduced to NiOx films to improve their electrical properties. The H2O2 treatment significantly facilitated Ni3+ formation, resulting in a deeper work function and valence band maximum of NiOx, which was confirmed by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. OSCs incorporating the H2O2-treated NiOx with a PM6:Y6 active layer have achieved a maximum power conversion efficiency (PCE) of 15.81% and an open-circuit voltage (Voc) of 0.827 V, surpassing the performance of control NiOx-based OSCs. Furthermore, NiOx-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 NiOx HTMs synthesized by the combustion method, thereby advancing the development of more efficient and stable OSCs.