Scalable Spray Processing Resolves the Dimensionality-Transport Trade-off in Lead-Free Indoor Photovoltaics

Scalable processing of lead-free perovskite-inspired absorbers is often constrained by a fundamental trade-off: the structural reconstruction needed to improve electronic dimensionality can simultaneously introduce anisotropic textures that hinder vertical charge extraction. Here we show that this trade-off can be overcome in vacancy-ordered antimony halides by coupling ultrasonic spray deposition with solvent- and halide-mediated crystallization control. Using Cs₃Sb₂I₉-xCl_x as a model system, we developed an ambient-air deposition process followed by annealing under an N₂/SbI₃ atmosphere route based on an amide-free 2-methoxyethanol/butanol solvent mixture that yields compact, pinhole-free films without high-boiling amide solvents. Chloride incorporation directs annealing-induced reconstruction from a zero-dimensional dimeric phase to a layered polymorph, while grazing-incidence wide-angle X-ray scattering reveals that this transformation occurs without generating a strongly detrimental crystallographic texture. Transient absorption spectroscopy further shows suppressed self-trapping and longer-lived band-edge carriers after dimensional reconstruction. As a result, the layered absorber retains an effective out-of-plane transport component and enables indoor photovoltaic (iPV) efficiencies up to 6.9% at 1000 lux (6500 K). Our results identify a general route by which scalable spray processing can be used not only to deposit lead-free absorbers, but also to engineer phase evolution and transport-relevant texture for efficient vertical optoelectronic operation.