In situ observation of ultra-giant spherulites in perovskite hydrates

Spherulitic growth-commonly observed in polymers-is shown here to be reproducible in lead-halide perovskite hydrates on glass substrates, yielding ultra-giant spherulites spanning the mm-1 cm scale under specific conditions.Here I introduce Hygro-Triggered Giant Spherulites Formation, an equipment-light process that transforms a routine spincoated MAPbI3-xClx precursor film into a ~1 cm-scale giant spherulites using only standard glovebox and hot-plate steps.A 3:1 MAI/PbCl₂ precursor (40 wt% in DMF or DMSO) is spin-coated on glass and annealed at 60 °C for 10 min under N₂ to produce a Cl-rich seed layer containing needle-like precursor crystallites.Subsequent exposure to ambient air (60-65% RH) reproducibly initiates a single surface nucleus that dominates growth and drives rapid two-dimensional radial expansion, completing within ~2 h.Realtime optical microscopy shows an advancing spherulite front that incorporates surrounding particles.Post-annealing at 90 °C for 4 h converts the white precursor network into black perovskite while preserving a pronounced out-of-plane (110) texture.Optical microscopy confirms centimeter-scale, single-nucleus spherulites with strong preferred orientation and far fewer macroscopically visible high-angle grain boundaries than conventional spin-coated films, with 100% yield across >50 trials.Under ambientair ageing tests, HT-GSF films exhibit only weak hydrate-related signatures after one week, whereas control films develop strong hydrate peaks and visible degradation within hours.The applications of HT-GSF are truly diverse.The first potential use is for certificates and PUFs.The nucleation points of spherulites are random, making counterfeiting inherently difficult.Furthermore, due to their extremely large size, they can be scanned by smartphones like QR codes.Therefore, they have high potential for global adoption.I will name certificates utilizing this principle "Spherulites Certificate."