Improved Anchoring of Self‐Assembled Monolayer on Hydroxylated NiO_x Film Surface for Efficient and Stable Inverted Perovskite Solar Cells

Abstract Self‐assembled monolayers (SAMs) have significantly improved the device performance of inverted perovskite solar cells (PSCs). However, the inadequate chemical bonding affinity between SAMs and the substrate as well as the uneven SAM distribution can lead to the decrease in device performance. Herein, the study reports a bilayer NiO_x hole transport layer (HTL), consisting of ultrathin NiO_x buffer film prepared through atomic layer deposition (ALD‐NiO_x) and spin‐coated NiO_x film (Spin‐NiO_x). The work function difference between the two NiO_x films will facilitate the hole transfer from the ALD‐NiO_x to the Spin‐NiO_x in the ALD‐NiO_x/Spin‐NiO_x bilayer structure. These holes will undergo surface hydroxylation reactions with water molecules on the Spin‐NiO_x film surface, generating additional hydroxyl groups covalently bonded to the Spin‐NiO_x film, which can provide more anchoring sites for SAM molecules. Stable covalent bonds can be formed between the Spin‐NiO_x film and the subsequently coated SAM film. As a result, SAM films with better coverage and molecular arrangement can be obtained. The ALD‐NiO_x/Spin‐NiO_x/SAM composite HTL also demonstrates superior charge transport capability and thermal stability. For small area PSCs (0.06 cm²) prepared by using the composite HTL, a champion power conversion efficiency (PCE) of 25.25% is achieved, and the device stabilities are also significantly improved.