Ligand-Free, Quantum-Confined Cs2SnI6 Perovskite Nanocrystals

Abstract

Tin-halide perovskite nanocrystals are a viable precursor for lead-free, high-efficiency active layers for photovoltaic cells. We describe a new synthetic procedure for quantum-confined Cs2SnI6 nanocrystals with size-dependent band gaps in the long-visible to near-infrared (1.38–1.47 eV). Hot injection synthesis produces particles with no organic capping ligands, with average diameters that increase from 12 ± 2.8 nm to 38 ± 4.1 nm with increasing reaction temperature. The band gap, energies of the first excitonic peak, ground-state bleach peak (in the transient absorption spectrum), and photoluminescence peak depend linearly on the inverse square of diameter, consistent with quantum-confined excitons with an effective mass of (0.12 ± 0.02)m0, where m0 is the mass of an electron, a factor of 4.6 smaller than that in the bulk material. Transient absorption measurements show that approximately 90% of the bleach amplitude decays within 30 ps, probably because of carrier trapping on unpassivated surface sites....