In-gap states in solar cell absorbers that are recombination centers determine the cell's photovoltaic performance. Using scanning tunneling spectroscopy (STS), temperature-dependent photoconductivity and steady-state photocarrier-grating measurements we probed, directly and indirectly, the energies of such states, both at the surface and in the bulk of two similar, but different halide perovskites, the single cation MAPbI3 (here MAPI) and the mixed cation halide perovskite, FA0.79MA0.16Cs0.05Pb(I0.83Br0.17)3 (here MCHP). We found a correlation between the energy distribution of the in-gap states, as determined by STS measurements, and their manifestation in the photo-transport parameters of the MCHP absorbers. In particular, our results suggest that the in-gap recombination centers in the MCHP are shallower than those of MAPI. This can be one explanation for the better photovoltaic efficiency of the former.
Bibliographical noteFunding Information:
At the Hebrew University this work was supported in part by ISF grant #661/16 and the Harry de Jur Chair in Applied Science (O.M.) and the Enrique Berman Chair in Solar energy research (I.B.). At the Weizmann Institute of Science this work was supported, in part by its Sustainability and Energy Research Initiative, SAERI (GH) and by grants from the Israel Ministry of Science and Technology. DC held the Schaefer Chair of Energy Research.
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