Water is often viewed as detrimental
to organic halide perovskite
stability. However, evidence highlights its efficacy as a solvent
during organic perovskite liquid synthesis. This paradox prompts an
investigation into water’s influence on perovskite nanoclusters.
Employing first principle calculations and ab initio molecular dynamics simulations, surprisingly, we discover some subsurface
layers of methylammonium lead iodide (MAPbI3) nanoclusters
exhibit stronger relaxation than surface layers. Moreover, a strong
quantum confinement effect enhances the band gap of MAPbI3 as the nanocluster size decreases. Notably, the water molecules
above MAPbI3 nanoclusters induce rich localized defect
states, generating low-lying shallow states above the valence band
for the small amounts of surface water molecules and band-like deep
states across the whole gap for large nanoclusters. This work provides
insights into water’s role in the electronic structure and
structural evolution of perovskite nanoclusters, aiding the design
of water-resistant layers to protect perovskite quantum dots from
ambient humidity