Enhanced Open-Circuit Voltage of Wide-Bandgap Perovskite Photovoltaics by Using Alloyed (FA1–xCsx)Pb(I1–xBrx)3 Quantum Dots

Abstract

We report a detailed study on APbX3 (A=Formamidinium (FA+), Cs+; X=I-, Br-) perovskite quantum dots (PQDs) with combined A- and X-site alloying that exhibit, both, a wide bandgap and high open circuit voltage (Voc) for the application of a potential top cell in tandem junction photovoltaic (PV) devices. The nanocrystal alloying affords control over the optical bandgap and is readily achieved by solution-phase cation and anion exchange between previously synthesized FAPbI3 and CsPbBr3 PQDs. Increasing only the Br- content of the PQDs widens the bandgap but results in shorter carrier lifetimes and associated Voc losses in devices. These deleterious effects can be mitigated by replacing Cs+ with FA+, resulting in wide bandgap PQD absorbers with improved charge-carrier mobility and PVs with higher Voc. Although further device optimization is required, these results demonstrate the potential of FA1–xCsx)Pb(I1–xBrx)3 PQDs for wide bandgap perovskite PVs with high Voc.