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Current-Induced Phase Segregation in Mixed Halide Hybrid Perovskites and its Impact on Two-Terminal Tandem Solar Cell Design
journal contribution
posted on 2017-07-24, 00:00 authored by Ian L. Braly, Ryan J. Stoddard, Adharsh Rajagopal, Alexander R. Uhl, John K. Katahara, Alex K.-Y. Jen, Hugh W. HillhouseMixed
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(I0.6Br0.4)3 and (MA0.9,Cs0.1)Pb(I0.6,Br0.4)3, 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, (FA0.83,Cs0.17)Pb(I0.66,Br0.34)3, 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.