Growth and Surface Treatment Strategies for Metal Halide Perovskite Single-Crystal Thin Films

Perovskite solar cells are leading candidates for next-generation photovoltaics owing to their high power conversion efficiency and excellent optoelectronic properties. Yet polycrystalline devices have plateaued below the Shockley–Queisser (SQ) limit, mainly because grain-boundary–induced nonradiative recombination and ion migration impede long-range charge transport and device stability. By contrast, Single-crystal thin films (SCTFs)―with intrinsically low defect densities and negligible grain boundaries―nominally offer a practical route toward the theoretical efficiency limit; however, current SCTF devices still fall short of the SQ limit, underscoring persistent surface and interface losses. Among fabrication routes, solution-processed space-confined growth, often leveraging inverse-temperature crystallization, has emerged as an effective strategy for producing high-quality SCTFs. This review synthesizes how growth parameters―solution chemistry, supersaturation, temperature gradients, gap thickness, and substrate wettability―govern thickness uniformity, crystallographic orientation, surface termination, and trap density. We highlight that residual-solution–induced secondary crystallization and high surface trap densities are primary sources of interfacial losses. Finally, we argue that closing the gap to the SQ limit requires coordinated solvent/interface engineering together with targeted surface treatments, underpinned by the establishment of a precise surface analysis framework and clear criteria for defining “true” SCTFs.