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Processing Dependent Influence of the Hole Transport Layer Ionization Energy on Methylammonium Lead Iodide Perovskite Photovoltaics

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posted on 19.04.2018, 00:00 by So Min Park, Samuel M. Mazza, Zhiming Liang, Ashkan Abtahi, Alex M. Boehm, Sean R. Parkin, John E. Anthony, Kenneth R. Graham
Organometal halide perovskite photovoltaics typically contain both electron and hole transport layers, both of which influence charge extraction and recombination. The ionization energy (IE) of the hole transport layer (HTL) is one important material property that will influence the open-circuit voltage, fill factor, and short-circuit current. Herein, we introduce a new series of triarylamino­ethynylsilanes with adjustable IEs as efficient HTL materials for methyl­ammonium lead iodide (MAPbI3) perovskite based photovoltaics. The three triarylamino­ethynylsilanes investigated can all be used as HTLs to yield PV performance on par with the commonly used HTLs PEDOT:PSS and Spiro-OMeTAD in inverted architectures (i.e., HTL deposited prior to the perovskite layer). We further investigate the influence of the HTL IE on the photovoltaic performance of MAPbI3 based inverted devices using two different MAPbI3 processing methods with a series of 11 different HTL materials, with IEs ranging from 4.74 to 5.84 eV. The requirements for the HTL IE change based on whether MAPbI3 is formed from lead acetate, Pb­(OAc)2, or PbI2 as the Pb source. The ideal HTL IE range is between 4.8 and 5.3 eV for MAPbI3 processed from Pb­(OAc)2, while with PbI2 the PV performance is relatively insensitive to variations in the HTL IE between 4.8 and 5.8 eV. Our results suggest that contradictory findings in the literature on the effect of the HTL IE in perovskite photovoltaics stem partly from the different processing methods employed.