Prashant Kamat1 Geetha Balakrishna1 2

1, University of Notre Dame, Notre Dame, Indiana, United States
2, Jain University, Bangalore, Karntaka, India

With the emergence of highly efficient lead halide perovskites there is a need to understand the excited state behavior and charge separation events following photoexcitation. Mixed halide lead perovskites offer a useful strategy for continuous tuning of the semiconductor bandgap. For example, by varying the halide composition of methylammonium lead iodide/bromide (CH3NH3PbBrxI3-x (x=0 to 3)) it is possible to tune the bandgap between 1.55 eV and 2.43 eV. In addition to photovoltaic applications these mixed halide perovskites offer rich photophysical properties with lasing applications. The excited state characterization using emission and transient absorption spectroscopy has allowed us to probe the photoinduced processes. Of particular interest are mixed halide lead perovskites (e.g.,CH3NH3PbI3-xBrx) which offer flexibility of tuning bandgap. Interestingly, they also undergo phase segregation to create Iodine-rich and Bromide- rich regions when subjected to visible irradiation. This intriguing aspect of halide ion movement in these mixed halide films can be tracked from the changes in the photoluminescence and absorption spectra. The photovoltaic performance of perovskite solar cells with varying degree of halide treatment will also be discussed