Post‐treatment‐Free Solution‐Processed Non‐stoichiometric NiOx Nanoparticles for Efficient Hole‐Transport Layers of Organic Optoelectronic Devices

High-quality non-stoichiometric NiOx nanoparticles are synthesized by a facile chemical precipitation method. The NiOx film can function as an effective hole-transport layer (HTL) without any post-treatments, while offering wide temperature applicability from room temperature to 150 °C. A high efficiency of 9.16% is achieved in organic solar cells using the NiOx HTL. A better performance in a NiOx-based organic light-emitting diode is observed, compared with a device using PEDOT:PSS.