Colloidal semiconductor quantum dots (QDs) are promising materials for realizing high-performance liquid-junction photovoltaic cells. Solar cells based on Zn:CuInSe2 QDs show high efficiency despite a large abundance of native defects typical of ternary I–III–VI2 semiconductors. To elucidate the reasons underlying the remarkable defect tolerance of these devices, we conduct side-by-side photovoltaic and spectroscopic studies of as-prepared and surface-modified Zn:CuInSe2 QDs. Using surface ligands with different lengths and binding affinities to the TiO2 surface, we tune the rates of both defect-related relaxation and QD-to-TiO2 electrode electron transfer. Despite their profound influence on photoluminescence dynamics, surface modifications have surprisingly little effect on photovoltaic performance suggesting that intragap defects do not impede but actually assist the photoconversion process in Zn:CuInSe2 QDs. These intragap states, identified as shallow surface-located electron traps and native Cu1+ hole-trapping defects, mediate QD interactions with the TiO2 electrode and the electrolyte, respectively, and help achieve consistent photovoltaic performance with ~85% photon-to-electron conversion efficiencies and highly reproducible power conversion efficiencies of 9–10%.
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The datasets generated and/or analysed during the current study are available within the paper, its Supplementary Information and its Source Data files.
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We thank J. Yu for supplying mesoporous-carbon cathodes and Y. Wang for assistance with the EQE measurements. The studies of QD photophysical properties, QD surface functionalization and charge transfer at the QD/TiO2 interface were supported by the Solar Photochemistry Program of the Chemical Sciences, Biosciences and Geosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy. The research into QD synthesis and device fabrication was supported by the Laboratory Directed Research and Development programme of Los Alamos National Laboratory (LANL) under project number 20190232ER. A.S.F. was supported by the LANL African American Partnership Program.
The authors declare no competing interests.
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Du, J., Singh, R., Fedin, I. et al. Spectroscopic insights into high defect tolerance of Zn:CuInSe2 quantum-dot-sensitized solar cells. Nat Energy 5, 409–417 (2020). https://doi.org/10.1038/s41560-020-0617-6
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