Bypassing the yellow phase for extremely stable formamidinium lead iodide perovskite solar cells
Summary
Using modeling and structural studies, we show that chloride incorporation in formamidinium lead iodide (FAPI) perovskites alters the energetics of both the formation and degradation pathways. We fabricated films with two coadditives 15 mole % FA chloride (FACl) and 0.5 mole % BA2PbI4, where BA is butylammonium), in which FACl ensures chloride incorporation and both additives collectively create a compressive lattice strain that stabilizes the FAPI black phase and bypasses the formation of
Content
# Bypassing the yellow phase for extremely stable formamidinium lead iodide perovskite solar cells
*Published: 2026 Apr 30*
Using modeling and structural studies, we show that chloride incorporation in
formamidinium lead iodide (FAPI) perovskites alters the energetics of both the
formation and degradation pathways. We fabricated films with two coadditives [15
mole % FA chloride (FACl) and 0.5 mole % BA2PbI4, where BA is butylammonium)],
in which FACl ensures chloride incorporation and both additives collectively
create a compressive lattice strain that stabilizes the FAPI black phase and
bypasses the formation of a yellow phase during degradation. The coadditive
strategy revealed a favorable transition from face-sharing 2H, 4H, 6H, and 8H
phases to the corner-sharing 3C black phase. Photovoltaic devices with a p-i-n
architecture had an average power conversion efficiency (40 devices) of 24.1%
and lost only 2% of their efficiency after 1200 hours at 85° ± 5°C, 1-sun
illumination, and open-circuit conditions. Upon stressing at 15-sun illumination
at 90°C for >400 hours, the stabilized black 3C phase degraded not through the
2H-PbI2 phase but through the energetically uphill 3R-PbI2 phase.
DOI: 10.1126/science.aeb7992