Herein, trifluoromethylation has proven to be an effective strategy for ultra-narrow band-gap NFAs. A PCE of 15.59% is achieved from BTIC-CF 3 -g-based devices, which is the highest value in reported ultra-narrow band-gap acceptors. A ternary device with 16.50% efficiency is also obtained, resulting from its red-shifted absorption. Meanwhile, the single-crystal structure of BTIC-CF 3 -g has been successfully presented, which gives a deep understanding of the solid-state molecular packings in these highly efficient acceptors.
The innovation of non-fullerene acceptors (NFAs) enables the rapid progress of organic solar cells (OSCs) in power conversion efficiencies to over 19%, endowing OSCs with great potential toward real-world application. In this critical review, we outline the recent advances of NFA-based OSCs -from ITIC-to Y6-family, to exemplify the structure-performance correlations, and cover from material chemistry to nanomorphology controlling. In addition, we point out the possible degradation mechanisms behind the NFA-based devices and strategies for mitigating the stability issues. With OSC efficiencies approaching 20% benchmark, increasing attention has been built-up toward the technology's applications. Therefore, we describe the opportunities and challenges in the promising applications, mainly on semitransparent and flexible OSCs for commercial photovoltaics. Finally, we provide a summary and perspective to point out the primary challenges the OSC technology is facing toward commercialization.
Noncovalent conformational lock (NCL)
is a beneficial noncovalent
intramolecular interaction that assists in maintaining the molecular
planar conformation. Such a planar conformation is favorable for a
shorter molecular distance and higher molecular crystallinity, further
yielding a more efficient charge transfer and higher power conversion
efficiency (PCE). In this contribution, a pair of isomeric small-molecular
nonfullerene acceptors (THP-4F and HPT-4F) were designed and synthesized
based on the central core modification. HPT-4F with a negligible dihedral
angle of 0.23° showed a highly planar conformation, bathochromic
absorption, higher charge mobility, suppressed charge recombination,
and enhanced J
sc and fill factor, leading
to a PCE of 8.68%, nearly 8 times higher than 1.31% of its isomer
THP-4F. This work gives a clear view of NCLs and molecular planarity
for molecular design and efficient organic photovoltaic materials
by comparing two structural isomers’ totally different properties.
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