Dr. S. W. Tsang’s paper is featured on back cover of J. Mater. Chem. A
Dr. Tsang and co-workers present a study on detrimental effects of mobile ions in perovskite solar cells on the device performance and stability. Mobile ions in perovskite films have been demonstrated to strongly affect both the device photovoltaic performance and stability. Photoluminescence and transient photocurrent results indicate that the mobile ions increase the nonradiative recombination and reduce the charge transporting properties, respectively. X-ray diffraction results show that the mobile ions trigger the deformation of perovskite to PbI2 during device operation.