Seed‐Assisted Cu‐Doped Chemical Bath Deposition for Preparing High‐Quality NiOx Hole‐Transport Layers in Perovskite Solar Cells

P‐type NiO x films are widely used as hole‐transport layers (HTLs) in p–i–n perovskite solar cells (PSCs) owing to their wide bandgap, stability, and optical transmittance. Chemical bath deposition (CBD) is an effective method for growing metal oxide HTLs. However, NiO x films prepared by the CBD method have pinholes because of their small grain size, which makes it difficult to cover the substrate in all directions, leading to severe carrier recombination at the interface between NiO x and perovskite. Herein, the device efficiency is improved from 18.13% to 22.51% using NiO x prepared by CBD with seed‐assisted growth and Cu‐ion doping as the HTL. The addition of crystal seeds significantly enhances the grain size, resulting in better substrate coverage by the prepared NiO x films. Cu‐ion doping improves the conductivity of the film and enhances its ability to extract holes. In addition, the results confirm that this method is suitable for the manufacturing of large‐area modules and has good reproducibility. This research demonstrates an effective CBD method for creating NiO x films for use in PSCs and offers a new approach for preparing inorganic HTLs using CBD.