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Colloidal quantum dots (QDs) are promising candidates for the next generation of photovoltaic (PV) technologies. Much of the progress in QD PVs is based on using PbS QDs, partly because they are stable under ambient conditions. There is considerable interest in extending this work to PbSe QDs, which have shown an enhanced photocurrent due to multiple exciton generation (MEG). One problem complicating such device-based studies is a poor stability of PbSe QDs toward exposure to ambient air. Here we develop a direct cation exchange synthesis to produce PbSe QDs with a large range of sizes and with in situ chloride and cadmium passivation. The synthesized QDs have excellent air stability, maintaining their photoluminescence quantum yield under ambient conditions for more than 30 days. Using these QDs, we fabricate high-performance solar cells without any protection and demonstrate a power …