Facile synthesis without involvement of toxic reagents is of great significance in the practical application of photovoltaic materials. In this work, four acceptor-donor-acceptor (AÀ DÀ A) type unfusedring acceptors (UFRAs) with stepwise extension in π-conjugation, i. e., CPFB-IC-n (n = 1-4), involving cyclopentadithiophene (CPDT) and 1,4-difluorobenzene (DFB) as cores, are facilely synthesized by an atom-, step-economic and labor-saving method through direct arylation of CÀ H bond (DACH). Among them, CPFB-IC-4 has the longest conjugation lengths among the molecular UFRA ever reported. The dependence of optoelectronic properties and photovoltaic performances of CPFB-IC-n (n = 1-4) on conjugation length were systematically investigated. CPFB-IC-2 with near zero highest occupied molecular orbital (HOMO) offsets (ΔE HOMO = 0.06 eV) achieves the highest power conversion efficiency (PCE), due to the significantly enhanced open voltage (V OC ) and short current (J SC ) caused by the balanced frontier molecular orbitals (FMOs) and complementary light absorption. Our work demonstrates that the optical properties and FMOs of UFRAs can be finely tuned by the stepwise elongation of conjugation lengths. Meanwhile, DACH coupling as a powerful tool here established will be a promising candidate for synthesizing high-performance oligomeric UFRAs.

The basal plane of MoS provides a promising platform for chemical functionalization and the hydrogen evolution reaction (HER); however, its practical utilization remains challenging due to the lack of active sites and its low conductivity. Herein, using first principles simulations, we first proposed a novel and effective strategy for significantly enhancing the activity of the inert MoS surface using a graphene oxide (GO) support (MoS/GOs). The chemical bonding of the functional groups (CH and NH) on the MoS-GO hybrid is stronger than that in freestanding MoS or MoS-graphene. Upon increasing the oxygen group concentration or introducing N heteroatoms into the GO support, the stability of the chemically functionalized MoS is improved. Furthermore, use of GOs to support pristine and defective MoS with a S vacancy (S-MoS) can greatly promote the HER activity of the basal plane. The catalytic activity of S-MoS is further enhanced by doping N into GOs; this results in a hydrogen adsorption free energy of almost zero (ΔG = ∼-0.014 eV). The coupling interaction with the GO substrate reduces the p-type Schottky barrier heights (SBH) of S-MoS and modifies its electronic properties, which facilitate charge transfer between them. Our calculated results are consistent with the experimental observations. Thus, the present results open new avenues for the chemical functionalization of MoS-based nanosheets and HER catalysts.

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Ternary strategy has attracted extensive attention for bulk heterojunction organic solar cells (BHJ OSCs) owing to their potentially improved light harvesting, cascaded energy levels, and optimized film morphology of binary BHJs. Herein, three novel star‐shaped unfused ring electron acceptors (SSUFREAs), i.e., H1–3, with and without fluorine‐substituent in phenyl core or peripheral group are designed and synthesized as third components via direct C–H arylation to incorporate into PM6:Y6 BHJ films. The structure–property–performance dependence study reveals that the isotropic charge transfer, complementary star‐shape structure and light absorption, and energy‐level cascades of H1–3 with PM6 and Y6 allow ternary BHJs to have higher power conversion efficiency (PCE) compared to the PM6:Y6 binary BHJ. Among them, the ternary BHJ involving fluorine‐free H1, i.e., H1:PM6:Y6, possesses the highest PCE (16.57%) owing to the high‐lying frontier molecular orbital and the enlarged torsion angle, which enhances open‐circuit voltage, inhibits the excessive crystallization of Y6, and facilitates exciton dissociation as well as collection. The findings indicate that SSUFREAs have great potential to serve as third components to optimize morphology and improve the open‐circuit voltage of BHJ OSCs.