Strain-Induced Type II Band Alignment Control in CdSe Nanoplatelet/ZnS-Sensitized Solar Cells

Abstract

Colloidal CdSe nanoplatelets (NPLs) deposited on TiO2 and overcoated by ZnS were explored as light absorbers in semiconductor-sensitized solar cells (SSSCs). Significant red shifts of both absorption and steady-state photoluminescence (PL) along with rapid PL quenching suggest a type II band alignment at the interface of the CdSe NPL and the ZnS barrier layer grown on the NPL layer, as confirmed by energy band measurements. The considerable red shift leads to enhanced spectral absorption coverage. Cell characterization shows an increased open-circuit voltage of 664 mV using a polysulfide electrolyte, which can be attributed to a photoinduced dipole effect created by the spatial charge separation across the nanoplatelet sensitizers. The observed short-circuit current density of 11.14 mA cm–2 approaches the maximal theoretical current density for this choice of absorber, yielding an internal quantum efficiency of close to 100%, a clear signature of excellent charge transport and collection yields. With thei...