Effect of FABr Over-Stoichiometry on the Morphology and Optoelectronic Properties of Wide-Bandgap FAPbBr_3 Films

G. Ammirati; F. Martelli; F. Toschi; S. Turchini; P. O'Keeffe; A. Paladini; F. Matteocci; J. Barichello; D. Di Girolamo; S. Piccirillo; A. Di Carlo; D. Catone

arXiv · 2511.19158

Effect of FABr Over-Stoichiometry on the Morphology and Optoelectronic Properties of Wide-Bandgap FAPbBr_3 Films

G. Ammirati·F. Martelli·F. Toschi·S. Turchini·P. O'Keeffe·A. Paladini·F. Matteocci·J. Barichello·D. Di Girolamo·S. Piccirillo·A. Di Carlo·D. Catone

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Abstract

In this study, we investigate the impact of formamidinium bromide (FABr) over-stoichiometry in the precursor solution on the optoelectronic properties and morphology of the resulting films of formamidinium lead bromide (FAPbBr_3). Optical characterization, including steady-state absorption, photoluminescence (PL), and femtosecond transient absorption spectroscopy, reveals a systematic blueshift in emission energy with increasing FABr content, attributed to the passivation of bromine vacancies and to the reduction of defect-assisted recombination. Power-dependent PL confirms this interpretation: the stoichiometric film exhibits a PL band due to donor-acceptor pair (DAP) recombination as identified by the typical excitation-dependent blueshift, whereas FABr-enriched samples show no evidence of DAP emission, indicating effective defect passivation. Additionally, morphological characterization shows a reduction in grain size with increasing FABr excess, indicating a trade-off between improved electronic quality and enhanced structural disorder. The film synthesized with a 5% excess of FABr provides the optimal balance, yielding the highest power conversion efficiency (6.26%), average visible transmittance (61.6%), and light utilization efficiency (3.85%). These results demonstrate that fine-tuning the precursor stoichiometry through controlled FABr addition represents a simple yet effective strategy to enhance the optoelectronic quality and performance of semitransparent perovskite solar cells.

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G. Ammirati, F. Martelli, F. Toschi, S. Turchini, P. O'Keeffe, A. Paladini, F. Matteocci, J. Barichello, D. Di Girolamo, S. Piccirillo, A. Di Carlo, D. Catone. 2025-11-24. Effect of FABr Over-Stoichiometry on the Morphology and Optoelectronic Properties of Wide-Bandgap FAPbBr_3 Films. https://arxiv.org/abs/2511.19158

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