Organic–inorganic hybrid halide perovskite solar
cells (PSCs)
have attracted substantial attention from the photovoltaic research
community, with the power conversion efficiency (PCE) already exceeding
26%. Current state-of-the-art devices rely on Spiro-OMeTAD as the
hole-transporting material (HTM); however, Spiro-OMeTAD is costly
due to its complicated synthesis and expensive product purification,
while its low conductivity ultimately limits the achievable device
efficiency. In this work, we build upon our recently introduced family
of low-cost amide-based small molecules and introduce a molecule (termed
TPABT) that results in high conductivity values (∼10–5 S cm–1 upon addition of standard ionic additives),
outperforming our previous amide-based material (EDOT-Amide-TPA, ∼10–6 S cm–1) while only costing an estimated
$5/g. We ascribe the increased optoelectronic properties to favorable
molecular packing, as shown by single-crystal X-ray diffraction, which
results in close spacing between the triphenylamine blocks. This,
in turn, results in a short hole-hopping distance between molecules
and therefore good mobility and conductivity. In addition, TPABT exhibits
a higher bandgap and is as a result more transparent in the visible
range of the solar spectrum, leading to lower parasitic absorption
losses than Spiro-OMeTAD, and has increased moisture stability. We
applied the molecule in perovskite solar cells and obtained good
efficiency values in the ∼15% range. Our approach shows that
engineering better molecular packing may be the key to developing
high-efficiency, low-cost HTMs for perovskite solar cells.