10.1021/acsenergylett.7b00525.s001 Ian L. Braly Ian L. Braly Ryan J. Stoddard Ryan J. Stoddard Adharsh Rajagopal Adharsh Rajagopal Alexander R. Uhl Alexander R. Uhl John K. Katahara John K. Katahara Alex K.-Y. Jen Alex K.-Y. Jen Hugh W. Hillhouse Hugh W. Hillhouse Current-Induced Phase Segregation in Mixed Halide Hybrid Perovskites and its Impact on Two-Terminal Tandem Solar Cell Design American Chemical Society 2017 incident light filter Current-Induced Phase Segregation phase segregation valence band holes FA MAC Mixed Halide Hybrid Perovskites 4 sun injection MA Br halide perovskites phase conduction band electrons FAC 1 sun equivalent CIGS bottom cell Two-Terminal Tandem Solar Cell Design Mixed halide 2017-07-24 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Current-Induced_Phase_Segregation_in_Mixed_Halide_Hybrid_Perovskites_and_its_Impact_on_Two-Terminal_Tandem_Solar_Cell_Design/5248336 Mixed halide hybrid perovskites are of significant interest because their bandgap can be tuned as a current-matched top-cell in tandem photovoltaics. However, several mixed halide perovskites phase segregate under illumination, exhibit large voltage deficits, and produce unstable photocurrents. We investigate the origin of phase segregation and implication for tandems with mixed halide large-bandgap (∼1.75 eV) perovskites. We show explicitly that MAPb­(I<sub>0.6</sub>Br<sub>0.4</sub>)<sub>3</sub> and (MA<sub>0.9</sub>,Cs<sub>0.1</sub>)­Pb­(I<sub>0.6</sub>,Br<sub>0.4</sub>)<sub>3</sub>, termed “MA” and “MACs”, respectively, rapidly phase segregate in the dark upon 1 sun equivalent current injection. This is direct experimental evidence that conduction band electrons or valence band holes are the culprit behind phase segregation. In contrast, (FA<sub>0.83</sub>,Cs<sub>0.17</sub>)­Pb­(I<sub>0.66</sub>,Br<sub>0.34</sub>)<sub>3</sub>, or “FACs,” prepared at only 75 °C resists phase segregation below 4 sun injection. FACs prepared at 165 °C yields larger grains and withstands higher injected carrier concentrations before phase segregation. The FACs and MACs devices sustain near constant power output at 1 sun and do not affect the current output of a CIGS bottom cell when used as an incident light filter.