Centimeter-Scale Giant-Grain Growth: Radial Expansion of MAPbI3-xClx Precursor Single Crystals from a Single Nucleus on Glass

Centimeter-scale single crystals are coveted in halide-perovskite optoelectronics but normally demand space-confined cells or slow, high-temperature growth. Here I report a radial Giant-Grain Growth (r-GGG) protocol that converts a routine spin-coated film into a quasi-single-crystalline MAPbI₃-ₓClₓ layer ~1 cm in diameter using only glovebox and hot-plate tools. A 3:1 MAI/PbCl₂ precursor solution (40 wt % in DMF) is spin-coated on glass and annealed at 60 °C for 10 min under N₂ to form a Cl-rich MAPbI₃-ₓClₓ seed layer. Subsequent exposure to ambient air at 60–65 % relative humidity triggers the spontaneous emergence of a single surface nucleus that monopolizes the solute supply and drives two-dimensional radial expansion; full lateral growth completes within ~2 h. Post-annealing at 90 °C for 4 h converts the white precursor needles into a black perovskite that retains a (002) out-of-plane orientation absent in conventional films. X-ray diffraction, SEM and time-lapse microscopy confirm centimeter-scale monodomains, sparse grain boundaries and exceptional reproducibility (100 % yield in >50 trials). Accelerated ageing reveals only faint hydrate peaks in r-GGG films after one week in air, whereas control films develop pronounced hydrate signatures and visible degradation within hours. By uniting single-crystal quality with thin-film practicality, r-GGG provides an equipment-light route toward high-efficiency, durable perovskite solar cells, photodetectors and X-ray imagers.