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

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.