The
role electron-transport layers (ETLs) play in perovskite solar
cells (PSCs) is still widely debated. Conduction band alignment at
the perovskite/ETL interface has been suggested to be an important
role for the performance of the solar cells. However, little is known
about the effects of work-function shifts on the solar-cell performance,
and specifically, the open-circuit voltage (V
OC). Here, the effects of surface modification of SnO2 ETLs using polar phosphonic acids are investigated, including the
effects on work function, surface energy, device performance, and
device stability in inert atmosphere. The phosphonic acid modifications
did not have a large effect on V
OC; however,
a sharp decrease in the overall device performance was found, mostly
due to reduced fill factors. When exposed to conditions of low oxygen
concentration, the phosphonic acid surface modified devices yielded
current–voltage (J–V) curves with considerably lower hysteresis than those based on unmodified
SnO2. This suggests that this modification method may be
valuable for achieving stabilized power conversion efficiency without
hysteresis.
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