Presentation Information
[7p-S201-7]Tuning the energy band gap of formamidinium lead iodide quantum dots
〇Svrcek Vladimir1, McDonald Calum1, Mierzaaihemaiti Abuduhebaier1, Mariotti Davide2, Takuya Matsui1 (1.National Institute of Advanced Industrial Science and Technology (AIST),, 2.University of Strathclyde, U.K.)
Keywords:
quantum dots,perovskites,solar cell
Formamidinium lead iodide quantum dots (FAPI QDs) have shown promise in single-junction solar cells with efficiencies over 19%. For multi-junction cells targeting over 50% efficiency, precise bandgap tuning is vital. While reducing QD size induces quantum confinement, it also leads to instability (delta-phase formation), surface defects, and weak confinement effects, requiring ultra-small, unstable QDs for significant bandgap shifts. To address this, we synthesized FAPI QDs using magnesium bromide (MgBr2), sodium iodide (NaI), and tin acetate (SnAc) as additives. This enabled bandgap tuning from 1.50 eV (FAPI + SnAc) and 1.61 eV (pure FAPI) to as high as 2.21 eV (FAPI + MgBr2 + NaI). NaI contributed to bandgap widening across compositions. High resolution transmission electron microscopy showed ~12 nm QDs, indicating that bandgap shifts stem from energy level changes rather than confinement. Stability varied with composition: SnAc QDs degraded quickly, while MgBr2 and NaI-based QDs remained stable for months. Ligand exchange produced smooth QD films, which were integrated with bulk FAPI to form graded layers in single-junction n-i-p solar cells. The impact of the widened bandgap will be further discussed.