2, Xi’an University of Technology, Xi’an, , China
3, African University of Science and Technology (AUST), Abuja, , Nigeria
4, Baze University, Abuja, , Nigeria
'Organic-Inorganic lead halide perovskite solar cells have emerged as one of the most promising thin film photovoltaic technology. However, stability of these solar cells over prolonged solar irradiation is a major concern and has not been thoroughly investigated. In this work, using lead-acetate as the source material, we have fabricated devices with the architecture, glass/ITO/PEDOT:PSS/MAPbI3/PCBM/Ag and obtained efficiency of about 13%. We investigate the effect of adding excess lead to the active layer on the photo-induced degradation of efficiency. This work demonstrates that 5% excess Pb in devices is the optimal concentration for devices in regards to efficiency and stability and that these devices are able to retain more than 50% of the initial efficiency after 1 hour of prolonged exposure. Characterization of samples before and after illumination reveals a decrease in charge carrier lifetimes and minor changes in crystallinity and morphology as observed by X-ray diffraction and scanning electron microscopy, respectively. These findings are attributed to the formation of PbI2 precipitates which nucleate at grain boundaries of the perovskite material. For the optimum amount of PbI2 in the grain boundary, there is an alteration of the band structure at the active layer and charge transport layer interface. For the optimum concentration of 5 mol% excess Pb, the device retains the initial efficiency under prolonged illumination.