Boosting Power Conversion Efficiencies of Quantum-Dot-Sensitized Solar Cells Beyond 8% by Recombination Control

At present, quantum-dot-sensitized solar cells (QDSCs) still exhibit moderate power conversion efficiency (with record efficiency of 6–7%), limited primarily by charge recombination. Therefore, suppressing recombination processes is a mandatory requirement to boost the performance of QDSCs. Herein, we demonstrate the ability of a novel sequential inorganic ZnS/SiO2 double layer treatment onto the QD-sensitized photoanode for strongly inhibiting interfacial recombination processes in QDSCs while providing improved cell stability. Theoretical modeling and impedance spectroscopy reveal that the combined ZnS/SiO2 treatment reduces interfacial recombination and increases charge collection efficiency when compared with conventional ZnS treatment alone. In line with those results, subpicosecond THz spectroscopy demonstrates that while QD to TiO2 electron-transfer rates and yields are insensitive to inorganic photoanode overcoating, back recombination at the oxide surface is strongly suppressed by subsequent inorganic treatments. By exploiting this approach, CdSexTe1–x QDSCs exhibit a certified record efficiency of 8.21% (8.55% for a champion cell), an improvement of 20% over the previous record high efficiency of 6.8%, together with an additional beneficial effect of improved cell stability.We acknowledge the Natural Science Foundation of China (nos. 21421004, 91433106, 21175043), the Science and Technology Commission of Shanghai Municipality (nos. 11JC1403100, 12NM0504101), the Fundamental Research Funds for the Central Universities in China, and the Max Planck Society and Universitat Jaume I project 12I361.01/1 for financial support. H.W. is a recipient of a fellowship of the Graduate School Materials Science in Mainz funded through the German Research Foundation in the Excellence Initiative (GSC 266)