Coherent transformation of metal halide perovskites

Metal-halide perovskites offer high optoelectronic performance but translating laboratory efficiencies into controllable, reproducible processes remains challenging. Perovskite crystallization is tracked by in situ multiwavelength absorption to show that coherent, layer-by-layer conversion of low-n intermediates to three-dimensional perovskite, quantified by a transformation index (TI), correlates with device quality. TI displays a Sabatier-type dependence on additive–precursor interaction strength and concentration, defining an engineering window for reproducible film formation. Within this window, post-treatment-free devices reach a champion power conversion efficiency of 26.40% with improved stability and reduced device scatter at laboratory scale. TI is extractable from an inline optical readout and provides a measurable metric for additive screening and process tuning. Its applicability to scalable deposition is further validated through slot-die coated mini-modules, offering a practical pathway for inline process control. Metal-halide perovskites promise high performance but achieving controllable and reproducible fabrication is difficult. Yang et al. track crystallization in real time and define a measurable index that guides processing conditions to produce efficient, stable devices with scalable control.