Hydroxyl-Terminated CuInS₂-Based Quantum Dots: Potential Cathode Interfacial Modifiers for Efficient Inverted Polymer Solar Cells

The use of interfacial modifiers on cathode or anode layers can effectively reduce the recombination loss and thus have potential to enhance the device performance of polymer solar cells. In this work, we demonstrated that hydroxyl-terminated CuInS₂-based quantum dots could be potential cathode interfacial modifiers on ZnO layer for inverted polymer solar cells. By casting of a thin film of CuInS₂-based quantum dots onto ZnO layer, the controlled devices show obvious enhancements of open-circuit voltage, short-circuit current, and fill factor. With an optimized interfacial layer with ∼7 nm thickness, an improvement of power conversion efficiency up to 16% is obtained and the optimized power conversion efficiency of PTB7-based (PTB7: poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl]]) polymer solar cells approaches 8.51%. Detailed analysis shows that the performance enhancement can be explained to the improved light absorption, modified work function, reduced surface roughness, and the increased electron transfer of ZnO cathode interlayer.