What question did this study set out to answer?

The aim is to understand how incorporating MAPbBr3 into FAPbI3 affects its properties and performance in solar cells, particularly under high humidity.

April 22, 2026Open Access

Impact of MAPbBr3 incorporation on (FAPbI3)1-x(MAPbBr3)x perovskite solar cells processed under high-humidity ambient conditions without use of additives

FCFrancisco Enrique Cancino‐GordilloUniversidad Nacional Autónoma de México CACarlos Fabián Arias‐RamosUniversidad Nacional Autónoma de México JLJosé Francisco López-PalaciosUniversidad Autónoma del Estado de Hidalgo

Key Points

The aim is to understand how incorporating MAPbBr3 into FAPbI3 affects its properties and performance in solar cells, particularly under high humidity.
Fabrication of (FAPbI3)1-x(MAPbBr3)x films under ambient humidity conditions without additives.
Structural analysis using X-ray diffraction to assess lattice and phase changes.
Optical and electronic evaluations, including Urbach energy analysis, to determine band gap and crystalline quality.
Higher MAPbBr3 content leads to improved structural stability and optoelectronic properties, evidenced by tunable band gap from 1.58 to 1.88 eV.
Devices achieve a maximum efficiency of 13.1% with (FAPbI3)0.7(MAPbBr3)0.3 composition.
The composition provides a balance between δ-phase suppression and moisture sensitivity, showing enhanced resistance against humidity.

Abstract

Formamidinium-methylammonium mixed-halide (FAMA) perovskites are promising candidates for high-performance and stable perovskite solar cells (PSCs). However, their preparation and stability under ambient conditions are a big challenge for large scale production. Here, we systematically investigate the influence of MAPbBr3 incorporation on the structural and optoelectronic properties of (FAPbI3)1-x(MAPbBr3)x films. Crucially, all films and devices are fabricated entirely under ambient conditions with high relative humidity (up to 65%), without the use of solutions additives or inert gas protection. X-ray diffraction analysis reveals that higher MAPbBr3 content induces lattice contraction, stabilizes the photoactive α-phase, and suppresses the formation of the detrimental δ-phase of FAPbI3. Correspondingly, optical analysis demonstrates a tunable band gap from 1.58 to 1.88 eV as MAPbBr3 content increases, which is consistent with the changes observed in the Pb-X-Pb bond angles and halide substitution. Parallel to these structural improvements, electronic evaluation via Urbach energy analysis confirms a substantial reduction in sub-bandgap states and crystalline disorder at higher MAPbBr3 compositions. Due to these improvements, devices fabricated under ambient conditions exhibit enhanced open-circuit voltage and fill factor, reaching a champion efficiency of 13.1% for (FAPbI3)0.7(MAPbBr3)0.3. Importantly, humidity-dependent tests identify (FAPbI3)0.7(MAPbBr3)0.3 as the optimal composition, balancing the benefits of δ-phase suppression and crystalline quality against the increased moisture sensitivity from excessive MA+. FAMA samples with a stabilized α-phase of FAPbI3 and a low PbI2 concentration show improved moisture resistance compared to pure FAPbI3, suggesting a potential pathway for more stable devices. These findings underscore the potential of compositionally engineered FAMA perovskites for efficient and scalable solar cell fabrication under realistic environmental conditions.

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