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 cm 2 ) 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.