High photoluminescence yield from organometal halide perovskite quantum dots confined in a mesoporous TiO2 template grown by rapid thermal annealing

Abstract

Herein, we demonstrate the room temperature growth of ultra-small perovskite quantum dots (QDs) on a mesoporous TiO2 template fabricated via a low temperature solvothermal route. FESEM image of pristine TiO2 template reveals various exposed facets, which are relatively smooth. Rapid thermal annealing (RTA) under vacuum transforms the template into highly porous TiO2 mesostructure. TEM images reveal uniform growth of perovskite QDs on the TiO2 templates. Size of perovskite QDs grown on RTA treated template (∼2 nm) is much smaller than that of furnace annealed template. Interestingly, the size of the as-grown perovskite QDs is fully consistent with the pore size of templates. CH3NH3PbBr3 QDs grown on RTA treated template exhibits ∼72 fold enhancement in PL intensity as compared to bulk Br3 film and ∼13 fold enhanced photoluminescence (PL) intensity as compared to that of non-RTA treated template. Similarly, CH3NH3PbI3 QDs exhibits ∼26 fold enhanced PL compared to bulk I3 film, and the PL peak is observed to be blue shifted by 13 nm as compared to that grown without RTA treatment. The absorption edge of perovskite QDs grown on RTA treated template is observed to be blue shifted. Our analysis reveals that due to the smaller size and high density of pores, perovskite QDs encaged in the TiO2 mesopores experience strong quantum confinement effect, resulting in the strong enhancement of PL intensity along with the blue shift of absorption edge/ PL peak caused by the band gap enlargement.