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

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 NiOx hole transport layer (HTL), consisting of ultrathin NiOx buffer film prepared through atomic layer deposition (ALD‐NiOx) and spin‐coated NiOx film (Spin‐NiOx). The work function difference between the two NiOx films will facilitate the hole transfer from the ALD‐NiOx to the Spin‐NiOx in the ALD‐NiOx/Spin‐NiOx bilayer structure. These holes will undergo surface hydroxylation reactions with water molecules on the Spin‐NiOx film surface, generating additional hydroxyl groups covalently bonded to the Spin‐NiOx film, which can provide more anchoring sites for SAM molecules. Stable covalent bonds can be formed between the Spin‐NiOx film and the subsequently coated SAM film. As a result, SAM films with better coverage and molecular arrangement can be obtained. The ALD‐NiOx/Spin‐NiOx/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. This work introduces an ultrathin NiOx buffer layer prepared by atomic layer deposition technique (ALD‐NiOx) buffer layer between the spin‐coated NiOx (Spin‐NiOx) and the ITO substrate. Interestingly, it is found that the insertion of the ALD‐NiOx buffer layer can promote the formation of covalently bonded hydroxyl groups through surface hydroxylation reactions, increase the hydroxyl group content on the Spin‐NiOx film surface, thereby increasing the anchoring sites for self‐assembled monolayer molecules and resulting in better efficiencies and stabilities of inverted perovskite solar cells.