Minimizing
the interfacial defects and improving the charge transferability
of charge-transfer layers have become the most important strategies
to boost the efficiency and stability of perovskite solar cells. However,
most molecular passivators currently employed to alleviate interfacial
defects generate poorly conductive aggregates at the interfaces, hindering
the extraction of charge carriers. Here, a holistic interface engineering
strategy employing a highly crystalline small molecule of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) is reported. We reveal that
C8-BTBT bridges the perovskite film to the hole-transporting layer
with reduced interfacial defects and improved charge carrier management.
Moreover, such interfacial modification with air-stable C8-BTBT achieves
a desirable and robust morphology of Spiro-OMeTAD by reducing the
aggregates. Accordingly, C8-BTBT-treated devices exhibit a great enhancement
to all photovoltaic performance characteristics with an absolute efficiency
improvement exceeding 2%. The C8-BTBT-modified Spiro-OMeTAD enables
decent thermal tolerance, which paves the way for enhancing the performance
of Spiro-OMeTAD-based perovskite optoelectronics.
Lithium bis(trifluoromethanesulfonyl)imide
(Li-TFSI) additive is
widely employed to improve the hole mobility of the hole-transporting
layer (HTL) in perovskite solar cells (PSCs). However, the hygroscopic
nature of Li-TFSI is not beneficial to the long-term stability of
PSCs. Herein, a new more water-resistant Li-PFSI is used to replace
Li-TFSI. As a result, the best power conversion efficiency (PCE) of
22.14% is achieved for Li-PFSI-treated PSCs, exceeding that of the
control cell with Li-TFSI (20.25%). Importantly, the Li-PFSI-based
cell shows impressive environmental and thermal stability. Moreover,
we first comparatively investigate the effect of the amount of fluorine
substitution in lithium salt (2F for Li-FSI, 6F for Li-TFSI, and 10F
for Li-PFSI) on the HTL’s physical properties and their photovoltaic
performance in PSCs. We found that more fluorine substitution can
improve the HTL charge-carrier transfer and photovoltaic performance
in PSCs. Our findings provide key missing information for designing
new additives toward efficient and stable PSCs.
Three cost-effective D-π-D hole transport materials (HTMs) with different π-bridge including biphenyl (SY1), phenanthrene (SY2) and pyrene (SY3) have been synthesized by one-pot reaction with cheap commercially available starting materials...
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