Dual Optimization of Bulk and Surface via Guanidine Halide for Efficient and Stable 2D/3D Hybrid Perovskite Solar Cells

Abstract In order to improve both performance and stability of perovskite solar cells, a design is provided by combining the advantages of high‐efficiency 3D perovskite solar cells (PSCs) and long‐term stability 2D PSCs. A 2D/3D hybrid perovskite film with a dual (bulk‐ and surface‐) passivation approach is realized, based on in‐depth discussion of the guanidine halide (GuX) passivation mechanisms. The approach can reduce the charge carrier losses in the bulk and prevent decomposition at the surface. Based on a combination of ab initio molecular dynamics simulations, Urbach energy, and photovoltage measurements, it is indicated that the engineered components of GuX salts are GuCl for bulk treatment and GuI surface treatment, respectively. The former can lower the nonradiative recombination, and the latter can prevent the halogen‐out. Moreover, drive‐level capacitance profiling is employed in the context of the 2D/3D perovskite structure for revealing and proving the passivation mechanism. The 2D/3D hybrid perovskites achieve long‐term stability (efficiency degradation <10% after 30 days without encapsulation) and significant enhanced efficiency (22.53%) compared with the efficiency (20.31%) of the control device. This work represents a rational design strategy for bulk and surface passivation treatment in 2D/3D hybrid perovskites.