Scalable Spray Processing Resolves the Dimensionality–Transport Trade‐off in Lead‐Free Indoor Photovoltaics
Francesco Lamberti, Remah Elrashedy, Arpita Sarkar, Marcello Righetto, Ribhu Bhatia, Pietro Ostellari, Nicola Dengo, Mariangela Ruggeri, Rosaria Verduci, Andrea Basagni, Carlo Scian, Manas Ranjan Samantaray, Abhisek Chakraborty, Zeynab Skafi, Thomas Meredith Brown, Guilin Liu, Jiacheng He, Zhubing He, Giovanna D'Angelo, Sara Pescetelli, Camilla Ferrante, Simone Meloni, Teresa Gatti, Antonio AgrestiABSTRACT
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 Cs 3 Sb 2 I 9 –xCl x as a model system, we developed an ambient‐air deposition process followed by annealing under an N 2 /SbI 3 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.