5 research outputs found
Alkoxy-Induced Near-Infrared Sensitive Electron Acceptor for High-Performance Organic Solar Cells
We develop a fused-ring electron
acceptor (IOIC3) based on naphtho[1,2-<i>b</i>:5,6-<i>b</i>′]dithiophene core with alkoxy side-chains and compare
it with its counterpart (IOIC2) with alkyl side-chains. Change in
the side-chains affects electronic, optical, charge transport, and
morphological properties of the analogues. Because of π-conjugative
effect and σ-inductive effect of the oxygen atoms, IOIC3 exhibits
a slightly upshifted HOMO level (−5.38 eV) and a downshifted
LUMO level (−3.84 eV) relative to IOIC2 (HOMO = −5.41
eV, LUMO = −3.78 eV), leading to red-shifted absorption and
smaller optical bandgap of 1.45 eV than that of IOIC2 (1.54 eV). IOIC3
exhibits a higher electron mobility of 1.5 × 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> than
IOIC2 (1.0 × 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>). Organic solar cells (OSCs) based on PTB7-Th:IOIC3
exhibit power conversion efficiency (PCE) as high as 13.1%, significantly
higher than that of PTB7-Th:IOIC2 (9.33%). The semitransparent OSCs
based on PTB7-Th:IOIC3 afford PCEs of up to 10.8% with an average
visible transmittance (AVT) of 16.4%, higher than those of PTB7-Th:IOIC2
(PCE = 7.32%, AVT = 13.1%)
Influence of Thiophene Moiety on the Excited State Properties of Push–Pull Chromophores
The magnitude of intramolecular charge-transfer
(ICT) in push–pull
chromophores and the fraction of delocalized excitation in multibranched
chromophores and conjugated polymers play a crucial role in high photovoltaic
efficiency of a solar cell. In this work, we present a joint theoretical
and experimental study aimed to understand the influence of thiophene
moiety on photophysical properties of push–pull chromophores
for solar cell application. It is found that insertion of a thiophene
moiety as the conjugated bridge enhances the magnitude of ICT in push–pull
chromophores due to the inductive effect of the thiophene moiety.
In addition, introduction of a thiophene moiety as the conjugated
side chain significantly increases transition dipole moment of the
chromophore, and as a consequence, interchromophoric coupling is enhanced,
giving rise to a larger fraction of delocalized excitation within
multibranched chromophores. The results presented here show that introduction
of a thiophene moiety in push–pull chromophores contributes
to the improvement of the photophysical properties necessary for highly
efficient solar cell performance
A Facile Planar Fused-Ring Electron Acceptor for As-Cast Polymer Solar Cells with 8.71% Efficiency
A planar fused-ring electron acceptor
(IC-C6IDT-IC) based on indacenodithiophene
is designed and synthesized. IC-C6IDT-IC shows strong absorption in
500–800 nm with extinction coefficient of up to 2.4 ×
10<sup>5</sup> M<sup>–1</sup> cm<sup>–1</sup> and high
electron mobility of 1.1 × 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. The as-cast polymer
solar cells based on IC-C6IDT-IC without additional treatments exhibit
power conversion efficiencies of up to 8.71%
High-Performance Electron Acceptor with Thienyl Side Chains for Organic Photovoltaics
We
develop an efficient fused-ring electron acceptor (ITIC-Th)
based on indacenodithieno[3,2-<i>b</i>]thiophene core and
thienyl side-chains for organic solar cells (OSCs). Relative to its
counterpart with phenyl side-chains (ITIC), ITIC-Th shows lower energy
levels (ITIC-Th: HOMO = −5.66 eV, LUMO = −3.93 eV; ITIC:
HOMO = −5.48 eV, LUMO = −3.83 eV) due to the σ-inductive
effect of thienyl side-chains, which can match with high-performance
narrow-band-gap polymer donors and wide-band-gap polymer donors. ITIC-Th
has higher electron mobility (6.1 × 10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) than ITIC (2.6
× 10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) due to enhanced intermolecular interaction
induced by sulfur–sulfur interaction. We fabricate OSCs by
blending ITIC-Th acceptor with two different low-band-gap and wide-band-gap
polymer donors. In one case, a power conversion efficiency of 9.6%
was observed, which rivals some of the highest efficiencies for single
junction OSCs based on fullerene acceptors
Effect of Alkyl Side Chains of Conjugated Polymer Donors on the Device Performance of Non-Fullerene Solar Cells
The influence of the chemical structure
of conjugated polymers
on the nanophase separation and device performance in fullerene-based
solar cells has been widely studied, while this is less investigated
in non-fullerene solar cells. In this work, we design three conjugated
polymers with different length of side chains, and we find that the
length of side chains has little influence on the quantum efficiencies
of non-fullerene solar cells. As a comparison, the length of side
chains has a significant effect on the quantum efficiencies of fullerene-based
solar cells. This indicates that morphology of the blended thin films
in non-fullerene solar cells is rather independent of the length of
the donor side chains, and the mechanism for morphology evolution
in the non-fullerene system is completely different from that in the
fullerene system. Our conclusion is confirmed by a variety of advanced
characterization techniques. The studies reveal that in blended thin
films based on the non-fullerene material the donor polymers with
different side chains have a similar coherence length of π–π
stacking, crystal size and domain purity, giving rise to similar internal
quantum efficiency and power conversion efficiency of the solar cells