Wide-Band Gap Small-Molecule Donors with Diester-Terthiophene Bridged Units for High-Efficiency All-Small-Molecule Organic Solar Cells

Abstract

It is crucial to maintain both an ordered intermolecular packing and deep highest occupied molecule orbital energy levels (E HOMO ) for cutting-edge organic solar cells (OSCs) with a high open-circuit voltage (V OC ). Although halogen substitution has become the most popular strategy to lower the E HOMO of donor materials, there still remains great room for exploring new approaches to construct wide-band gap small-molecule donors (SMDs) with a deeper E HOMO . For this purpose, in this work, we primarily took a strategy of diester-terthiophene as a π-bridged unit to construct a type of wide-band gap SMDs named BER6 and BECN with an A−π−D−π−A framework using alkyl-thienyl-substituted benzo-dithiophene as a central electron-donating (D) unit and rhodanine or cyanoacetate derivatives as a terminal electron-accepting (A) unit. It is found that both molecules have almost coincident coplanarity and dipole interaction for the diesterterthiophene unit. As a result, an ordered molecular stacking and a deep E HOMO of about −5.40 eV with an optical band gap of 1.85−1.91 eV are presented for both molecules. A high power conversion efficiency of 9.03% with a high V OC of 0.97 eV was obtained in the BER6/IDIC-based all-smallmolecule OSCs (ASM-OSCs). Our results demonstrate that diester-terthiophene is a promising strategy to develop wide-band gap SMDs applied in high-performance ASM-OSCs.

Designing Benzodithiophene-Based Small Molecule Donors for Organic Solar Cells by Regulation of Halogenation Effects

“…The structure of the donor (or acceptor) is the foundation of related photophysical and photochemical properties . For the sake of exploring the factors affecting the properties of donors, it is necessary to discuss the molecular structure.…”

Progress and Future Potential of All-Small-Molecule Organic Solar Cells Based on the Benzodithiophene Donor Material

“…In 2021, two new BDT-based A−π−D−π−A configurations, BER6 and BECN, consisting of diester-terthiophene as a π-bridged unit and alkyl rhodanine or alkyl cyanoacetate as a terminal electron-acceptor unit, were designed and reported. The BER6/IDIC-based devices displayed an efficient PCE of 9.03%, while the devices based on BECN/IDIC displayed a much lower PCE of 5.52% owing to unevenly distributed microcrystalline particles on the surface of BECN/IDIC [ 95 ]. Two new small molecules with a central BDT donor, G17 and G19, using cyclopentadithiophene (CPDT) and dithienosilole (DTS) as the π donor moieties, respectively, were synthesized and reported.…”

Over 17% efficiency all-small-molecule organic solar cells based on an organic molecular donor employing a 2D side chain symmetry breaking strategy

“…The structural tunability of these SMDs is illustrated in terms of synthetic strategies based on three major components: (1) the electrondonating core with pendent side chains, (2) the solubilizing p bridge, and (3) the electron-withdrawing end group (EG). 7,12,24,[30][31][32][33][34][35][36] In these strategies, the electron-donating cores with pendent side chains are considered to be the key components in establishing the intramolecular ''push-pull effect'' and increasing the solubility. A variety of approaches, such as modulation of aromatic topology, halogenation, and substitution sites, have been explored to probe the functions of different side chains, which have been a cutting-edge research hotspot with the aim of improving the device performance.…”