Publication date: 3rd July 2020
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 exhibits, 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-xCsxPb(I1-xBrx)3 PQDs for wide bandgap perovskite PVs with high Voc.
This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. The QD synthesis was developed in the Laboratory Directed Research and Development program at NREL. The QD device fabrication acknowledges the Operational Energy Capability Improvement Fund of the Department of Defense. Time-resolved characterization at NREL was funded by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office. Funding for the work at The University of Texas was provided by the Robert A. Welch Foundation (F-1464) and the National Science Foundation through the Industry/University Cooperative Research Center (IUCRC) for Next Generation Photovoltaics (IIP-1540028 and IIP-1822206). M.S. would like to acknowledge the U.S. DOE, Office of Science, Office of Workforce Development for Teachers and Scientists, Science Undergraduate Laboratory Internship (SULI) Program for funding in 2017 and 2018. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government.
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