A Self-Organized Poly(vinylpyrrolidone)-Based Cathode Interlayer in Inverted Fullerene-Free Organic Solar Cells

Herein, poly(vinylpyrrolidone) (PVP) is used as the cathode interlayer (CIL) through the self-organization method in inverted organic solar cells (OSCs). By coating a solution of PVP and active layer materials onto a glass/indium tin oxide (ITO) substrate, the PVP can segregate to the near ITO side due to its high surface energy and strong intermolecular interaction with the ITO electrode. The power conversion efficiency (PCE) of the obtained OSC device reaches 13.3%, much higher than that of the control device with a PCE of only 10.1%. The improvement results from the increased exciton dissociation efficiency and the depressed trap-assisted recombination, which can be attributed to the reduced work function of the cathode by the self-organized PVP. Additionally, the molecular weight of the PVP has almost no influence on the device performance, and the PVP-modified device presents superior stability. This method can also be applied in other highly efficient fullerene-free OSCs, and with a fine selection of the active layer, a high PCE of 14.0% is obtained. Overall, this work demonstrates the great potential of the PVP-based CIL in inverted OSCs fabricated via the self-organization method.