Conformal Charge Transport Layers for Perovskite Solar Cells and Tandem Devices

Lead halide perovskite solar cells (PSCs) have demonstrated unprecedented progress, with a certified efficiency of 27% recently achieved. As critical components of PSCs, charge transport layers (CTLs) play pivotal roles in advancing device performance by regulating charge transport dynamics, modulating optical properties, and influencing the quality of overlying perovskite absorbers. In recent years, conformal CTLs, featuring full surface coverage, uniform thickness, and precise replication of the underlying substrate topography, have emerged as an ideal structure, enabling multiple efficiency records in PSCs. This review systematically elucidates the fundamental characteristics of conformal CTLs, critically analyzes advanced deposition technologies, and highlights advances in both single-junction PSCs and perovskite-based tandem solar cells (TSCs), with particular emphasis on technical adaptations to achieve CTLs with enhanced conformality or improved compatibility with textured surfaces and delicate perovskite layers. Finally, the current challenges and future research directions for developing high-performance CTLs in PSCs and TSCs are thoroughly discussed.