Round-comb FeO@SnO heterostructures enable efficient light harvesting and charge extraction for high-performance all-inorganic perovskite solar cells.

The precise design of an electron transport layer (ETL) to improve the light-harvesting and quality of perovskite (PVK) film plays a crucial role in the photovoltaic performance of n-i-p perovskite solar cells (PSCs). In this work, a novel three-dimensional (3D) round-comb FeO@SnO heterostructure composites with high conductivity and electron mobility induced by its Type-II band alignment and matched lattice spacing is prepared and employed as an efficient mesoporous ETL for all-inorganic CsPbBr PSCs. Arising from the multiple light scattering sites provided by the 3D round-comb structure, the diffuse reflectance of FeO@SnO composites is increased to improve the light absorption of the deposited PVK film. Besides, the mesoporous FeO@SnO ETL affords not only more active surface for sufficient exposure to the CsPbBr precursor solution but also a wettable surface to reduce the barrier for heterogeneous nucleation, which realizes the regulated growth of a high-quality PVK film with less undesired defect. Hence, both the light-harvesting capability, the photoelectrons transport and extraction are improved, and the charge recombination is restrained, delivering an optimized power conversion efficiency (PCE) of 10.23 % with a high short-circuit current density of 7.88 mA cm for the c-TiO/FeO@SnO ETL based all-inorganic CsPbBr PSCs. Moreover, under lasting erosion at 25 °C and 85 % RH for 30 days and light-soaking (AM 1.5G) for 480 h in air atmosphere, the unencapsulated-device shows superiorly persistent durability.