The Effects of Ion Substitution on Perovskite Film Degradation in Controlled Humidity Environments

The demand for clean, renewable energy grows constantly as time progresses and harvesting solar energy has been identified as one of the key pieces in solving this puzzle. Through ambipolar diffusion and high absorption characteristics, perovskite based solar cells have seen a large jump in device efficiency over a short amount of time. Perovskite cells are also appealing due to their low cost and ease of manufacturing, with the potential of competing with silicon based solar cells in the future. However, stability issues due to environmental factors, such as reactivity to atmospheric moisture, have plagued perovskites. These issues often lead to the deterioration of the material and a corresponding loss of efficiency in the devices. To remedy this, the introduction of various ions into the perovskite crystal structure has been proposed. In order to determine how these substitutions affect films in controlled atmospheric conditions, in situ testing and a spectrum of material characterization measurements were completed. Namely, by altering the relative humidity in a sealed test chamber housing perovskite samples and subjecting the films to these controlled conditions over extended periods, degradation was observed. The effects of the addition of formamidinium (FA) and bromine ions into the perovskite crystal structure was tested through the fabrication of MA0.7FA0.3PbI3 and MA0.7FA0.3Pb(I0.9Br0.1)3 films and comparing them to MAPbI3 perovskite films. Characterizing the films yielded insight into the degradation pathway and kinetics. Overall, the addition of FA ions appeared to have adverse effects on the stability of the films while the addition of bromine ions appeared to increase the stability of the films from a humidity exposure standpoint. This was concluded as half-lives for the MAPbI3, MA0.7FA0.3PbI3, and MA0.7FA0.3Pb(I0.9Br0.1)3 films under 85% relative humidity were 31 hours, 9 hours, and 15 hours respectively. Using this data and experimentation method, a balance of device efficiency and film stability can be reached in order to find the best perovskite for general application