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

We report a detailed study on APbX(3) (A = formamidinium (FA(+)), Cs+; X = I-, Br-) perovskite quantum dots (PQDs) with combined A- and X-site alloying that exhibits both a wide bandgap and high open-circuit voltage (V-oc) 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 FAPbI(3) and CsPbBr3 PQDs. Increasing only the Br- content of the PQDs widens the bandgap but results in shorter carrier lifetimes and associated V-oc 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 V-oc. Although further device optimization is required, these results demonstrate the potential of FA(1-x)Cs(x)Pb(I1-xBrx)(3) PQDs for wide-bandgap perovskite PVs with high V-oc.