Polymer Doping for High-Efficiency Perovskite Solar Cells with Improved Moisture Stability

Each component layer in a perovskite solar cell plays an important role in the cell performance. Here, a few types of polymers including representative p-type and n-type semiconductors, and a classical insulator, are chosen to dope into a perovskite film. The long-chain polymer helps to form a network among the perovskite crystalline grains, as witnessed by the improved film morphology and device stability. The dewetting process is greatly suppressed by the cross-linking effect of the polymer chains, thereby resulting in uniform perovskite films with large grain sizes. Moreover, it is found that the polymer-doped perovskite shows a reduced trap-state density, likely due to the polymer effectively passivating the perovskite grain surface. Meanwhile the doped polymer formed a bridge between grains for efficient charge transport. Using this approach, the solar cell efficiency is improved from 17.43% to as high as 19.19%, with a much improved stability. As it is not required for the polymer to have a strict energy level matching with the perovskite, in principle, one may use a variety of polymers for this type of device design.