Non-selective adsorption of organic cations enables conformal surface capping of perovskite grains for stabilized photovoltaic operation

Chemical passivation of defective perovskite surface is a fundamental strategy to stabilize solar cell operation by impeding the defect-dominant surface ion migration. Here, we show that the configuration of organic cations plays a key role in determining their surface adsorption energetics at various perovskite facets, which will strongly impact the spatial uniformity of the low-dimensional perovskite passivation layer (LDPL). A weak-anisotropic adsorption behavior is demonstrated for tertiary ammonium that can enable a conformal LDPL on the perovskite grain surface. Benefiting from comprehensive surface passivation, the migration of ionic perovskite species was suppressed and the as-fabricated p-i-n solar cells yielded an optimized power conversion efficiency of 22.6% with an expected T₈₀ lifetime of about 4,000 h under continuous 1-sun illumination. Our findings give insight into the design and preparation of heterostructured perovskite films toward efficient and stable solar cells.