Manipulating the Migration of Iodine Ions via Reverse-Biasing for Boosting Photovoltaic Performance of Perovskite Solar Cells

Perovskite solar cells (PSCs) are being developed rapidly and exhibit greatly potential commercialization. Herein, it is the first time to find that the device performance can be improved by manipulating the migration of iodine ions via reverse-biasing, for example, at -0.4 V for 3 min in dark. The exploration of this intriguing phenomenon indicates that the reverse bias can increase the charge recombination resistance, improve the carrier transport and enhance the built-in electric field. Furthermore, iodine ions including iodine interstitials in perovskites are confirmed to migrate and accumulate at the SnO2/perovskite interface under reverse-basing, which fill the iodine vacancies at the SnO2/perovskite interface and interact with the SnO2. First-principles calculations suggest that the SnO2/perovskite interface with less iodine vacancies has a stronger interaction and higher charge transfer, leading to larger built-in electric field and improved charge transport. Iodine ions that may pass through the SnO2/perovskite interface have also been confirmed to be able to interact with Sn4+ and passivate oxygen vacancies on the surface of SnO2. As a result, an efficiency of over 23% with the open-circuit voltage of 1.17 V has been achieved for reverse-biased PSCs. These results are of great significance to improve the device performance via utilizing the ion migration and reveal the physics mechanism of PSCs under reverse bias.