Control of Lattice Strain in α-FAPbI3 Film

초록

Control of residual lattice strain has recently emerged as a key strategy to not only govern the phase stability of α-formamidinium lead triiodide (α-FAPbI3) but also manipulate its band structure. Here, we employed an interlayer (IL) between SnO2 and perovskite, where the heteroepitaxial crystal growth of perovskite film with varied residual lattice strain was enabled by tuning the interplanar lattice spacing (d) corresponding to the (002) plane of IL, ranging from 0.329 nm for Cl-based IL to 0.340 nm for Br-based IL, as evidenced by transmission electron microscopy. The minimum d-mismatch between IL and α-FAPbI3 was monitored from the Br-based IL, effectively relieving the residual tensile strain across the perovskite film and thus resulting in the enhanced phase stability of α-FAPbI3. The employment of Br-based IL indeed induced a beneficial energy level alignment with defect passivation, which effectively suppressed the interfacial charge recombination and led to a notable increase in open-circuit voltage. Therefore, the improved power conversion efficiency (PCE) of the strain-engineered device was well maintained over 2000 h in ambient air, in contrast to a PCE drop by ≈27% for the control device without IL over 1000 h. © 2026 The Author(s). Small Structures published by Wiley-VCH GmbH.

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