Sub-Diffraction Nanolithography of Halide Perovskite via Reversible All-Optical Crystallization-Decomposition

Halide perovskites exhibit exceptional optoelectronic properties, yet their intrinsic chemical fragility and ionic nature pose fundamental challenges for high-resolution patterning and nanoscale integration. Here we report a reversible, all-optical structural modulation strategy that enables chemistry-free, sub-diffraction patterning of halide perovskite thin films through light-driven crystallization-decomposition dynamics. Localized femtosecond laser excitation induces controlled crystallization and an orthorhombic-to-cubic phase transition in CsPbBr₃ thin films, markedly enhancing crystallinity and optoelectronic response. In contrast, ultraviolet illumination promotes defect formation and partial decomposition into CsBr and PbBr₂, reversibly suppressing crystallinity and photocurrent. This optically driven crystallization-decomposition cycle is repeatable over multiple iterations with more than 85% photocurrent recovery, establishing a robust platform for reversible material-state control. Leveraging the nonlinear competition between laser-induced crystallization and UV-induced inhibition, we further demonstrate resist-free, sub-diffraction nanolithography with feature sizes down to 93.5 nm, well beyond the conventional optical diffraction limit. This work reveals a light-programmable structural degree of freedom in halide perovskites and provides a general materials framework for reconfigurable perovskite architectures, adaptive photonics, and dynamic optoelectronic systems.