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^–3 cm² V^–1 s^–1 than IOIC2 (1.0 × 10^–3 cm² V^–1 s^–1). 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 × 10⁵ M^–1 cm^–1 and high electron mobility of 1.1 × 10^–3 cm² V^–1 s^–1. 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^–4 cm² V^–1 s^–1) than ITIC (2.6 × 10^–4 cm² V^–1 s^–1) 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