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 CsPbBr 3 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(I 1– x Br x ) 3 PQDs for wide-bandgap perovskite PVs with high V oc .