Iodine-doped graphite carbon nitride for enhancing photovoltaic device performance via passivation trap states of triple cation perovskite films

Until now, the organic and inorganic hybrid perovskite solar cells have developed rapidly and obtained spectacular photovoltaic performance. However, the intrinsic trap states of solution-processed perovskite are still the critical issue hindering its development. Herein, the iodine-doped graphite carbon nitride (g-CNI) was introduced into the triple cation perovskite film in order to increase its crystallinity and passivate the trap states. The characterization results indicate that the doped iodine in g-CNI can interact with under-coordinated Pb ions at the grain boundaries and the surface of perovskite materials and the trap states can be effectively passivated. The reduction of trap state density inhibits the recombination of charge carriers, and facilitates the extraction and transport of charge carriers, which was characterized by photoluminescence measurements, open-circuit voltage decay and electrochemical impedance spectroscopy. Consequently, the devices of the perovskite with g-CNI achieved a champion PCE of 18.28%, which is higher than that of the control devices (16.57%). This work develops a simple and efficient strategy to passivate the trap states of perovskite films using a type of readily available polymer with a 2D pi electron structure.