Publication date: 11th March 2026
Chloride-based additive engineering is a widely used strategy to enhance crystallinity in perovskite solar cells, typically via methylammonium chloride (MACl)[1],[2]. In FA0.9Cs0.1Pb(I0.9Br0.1)3 films, we observed that increasing MACl concentration promotes preferred orientation along the (100) diffraction plane and grain growth, but introduces a trade-off: X-ray diffraction reveals peak splitting at the (200) and (300) planes, accompanied by a secondary photoluminescence (PL) emission at ~814 nm in addition to the primary peak around 770-780 nm. These signatures indicate segregation into lower-bandgap, halide-rich domains that act as recombination centers and lead to poor device reproducibility (CV = 37.4%).
To resolve this, we replaced MACl with methylammonium lead chloride (MAPbCl3) precursors. This substitution eliminates both the splitting of the diffraction peaks and the 814 nm PL secondary peak, and increases the carrier lifetime eightfold, from ~180 ns to ~1.6 μs. However, MAPbCl3 does not reproduce the grain coarsening observed with MACl, limiting further optoelectronic gains.
To simultaneously achieve phase purity, large grains, and good optoelectronic properties, we introduced pyrrolidinium-based secondary additives into the MAPbCl3-stabilized system. Pyrrolidinium chloride (PyCl) primarily passivates electronic defects, extending carrier lifetime to ~3.8 μs without substantial morphological change, whereas pyrrolidinium thiocyanate (PySCN) enables ~5x grain growth while reducing trap density. Combining MAPbCl3 (phase stability) with PySCN (morphology control) yields phase-pure films with a carrier lifetime of ~4.9 μs. Proof-of-concept devices using unoptimized copper thiocyanate (CuSCN) hole-transport layers deliver peak PCE of 14.9% (active area 0.2 cm2) with VOC=1.05 V, JSC=21.4 mAcm-2, and FF ≈ 67%, alongside improved reproducibility (CV=6.1%). The gap between long carrier lifetime and moderate PCE indicates that interfacial/transport losses—rather than bulk recombination—currently limit device performance, highlighting a clear pathway for architectural optimization. This work establishes a protocol that decouples crystallization kinetics from defect management, providing a pathway to reliable, high-quality perovskite photovoltaics.
This work was supported by a SECIHTI doctoral scholarship and by funding from the French government, managed by the National Research Agency (ANR) under the Investments for the Future program (reference: ANR-10-LABX-0074-01, Sigma-LIM). The authors are grateful to Nicolas Parou and the PLATINOM technology platform, a shared facility of the University of Limoges, which hosted all stages of the device fabrication and characterization.
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