Enhanced hole extraction through in situ mixed self-assembled molecules for efficient inverted perovskite solar cells

Self-assembled monolayers (SAMs), owing to their amphiphilic nature, tend to aggregate, which impedes the formation of a dense and uniform SAM on the substrate. Additionally, the weak adsorption ability of SAMs on the indium tin oxide (ITO) surface and the desorption of hydroxyl (OH) from the ITO surface induced by polar solvents can lead to the formation of vacancies. Herein, a dimethylacridine-based SAM is incorporated into the perovskite precursor solution. This SAM can be extruded from the precursor solution and enriched on the bottom surface of the perovskite, filling the vacancies and in situ forming a mixed SAM with MeO-2PACz as a hole-selective layer (HSL). The in situ formed mixed SAM optimizes the energy level alignment between the HSL and the perovskite, facilitating hole extraction and alleviating the residual strain of the perovskite film. Consequently, the perovskite solar cells (PSCs), based on the mixed SAM, achieve a power conversion efficiency (PCE) of 25.69% and exhibit excellent operational stability. When this approach is applied to 1.78 eV bandgap PSC devices, it yields a PCE of 20.08%. This work presents a unique strategy for fabricating both high-quality perovskite films and superior buried interfaces, which is also applicable to wide-bandgap PSCs.