Deciphering the role of impurities in methylammonium iodide and their impact on the performance of perovskite solar cells(Conference Presentation)

Solution based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, we have investigated the purity levels of common perovskite precursor solutions and found a number of impurities which are most critically controlling the crystallization of perovskites. Moreover, we identified these impurities at different level of concentrations is all commercially available precursors. In detail, we present a detailed chemical study on the nature of the various impurities in CH3NH3I and explored their impact on the crystal formation. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity free precursors vs precursors containing different concentrations of impurities. Most interestingly, we revealed that a certain concentration of impurities is detrimental to facilitate the growth of large grained crystals. This study gives valuable insight into the rate determining steps of perovskite crystal growth and provides the basis for developing reliable and reproducible high performance recipes for Perovskite solar cell processing.