Transporting holes stably under iodide invasion in efficient perovskite solar cells

Highly efficient halide perovskite solar cells generally rely on lithium-doped organic hole transporting layers that are thermally and chemically unstable, in part because of migration of iodide anions from the perovskite layer. We report a solution strategy to stabilize the hole transport in organic layers by ionic coupling positive polymer radicals and molecular anions through an ion-exchange process. The target layer exhibited a hole conductivity that was 80 times higher than that of the conventional lithium-doped layer. Moreover, after extreme iodide invasion caused by light-soaking at 85°C for 200 hours, the target layer maintained high hole conductivity and well-matched band alignment. This ion-exchange strategy enabled fabrication of perovskite solar cells with a certified power conversion efficiency of 23.9% that maintained 92% under standard illumination at 85°C after 1000 hours.