Producing p-Doped Surface for Hole Transporting Layer-Free Nonfullerene Organic Solar Cells.

Hole transporting layer-free organic solar cells with simplified device structures are desirable for their mass production. In this work, a p-dopant of organic molybdenum peroxide (OMP) to dope nonfullerene active layers to produce p-doped surface on the active layer is adopted. The OMP can effectively dope widely used polymer donors of nonfullerene organic solar cells, i.e., PTB7-Th, PBDB-T, and even PBDB-T-2F that has a very deep highest occupied molecular orbital (HOMO) energy level of -5.47 eV. The doping mechanism lies in the strong oxidizing property of peroxide groups of the OMP leading to superior doping properties. In the end, hole transporting layer-free nonfullerene organic solar cells with the device structure of ITO/PEI-Zn/PBDB-T-2F:IT-4F/Ag are fabricated. The cells show a power conversion efficiency of 12.2% and good thermal stability.