ABSTRACT
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 (A-D-A) type unfused-ring 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 C-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 (ΔEHOMO =0.06â eV) achieves the highest power conversion efficiency (PCE), due to the significantly enhanced open voltage (VOC ) and short current (JSC ) 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.
ABSTRACT
Although promising progress has been made in near-infrared (NIR) electron acceptors for broadening photoresponse of optoelectronics, there are still strong needs for efficient NIR materials with low synthetic complexities. In this work, three simple NIR acceptors are developed with absorption up to 1000 nm and possessing the same dithiophene cores with varied heteroatom linkages to carbon (C) atom for W1, to silicon (Si) for W2, and to nitrogen (N) for W3. It is found that the tuning of only one atom for simple acceptors can surprisingly lead to a large difference in photoelectric properties and solid stacking, as well as the performance in optoelectronics. Although quite simple, these electron acceptors, especially W1 (C), can also perform quite efficiently as organic photovoltaics (OPVs) as well as sensitive organic photodetectors (OPDs) when blended with PTB7-Th polymer. It is worthy to note that, among the representative NIR acceptors with over 950 nm absorption, W1 possesses one of the best figure-of-merit when considering the photoelectric performance versus synthetic complexity of materials. As a result, the PTB7-Th:W1-based OPDs reach a fast temporal response, ultralow-light intensity detection of 1.70 × 10-11 W·cm-2, and a high specific detectivity of 4.28 × 1012 cm·Hz1/2·W-1 at 830 nm, representing a highly sensitive self-powered OPD approach the commercial broadband silicon detectors. These simple structure materials provide a potential example for further application of NIR electron acceptor.
ABSTRACT
We report that variation of a single regio-configuration in molecular Janus particles leads to divergent self-assembly behaviors where each isomer gives a distinct morphology as guided by their molecular symmetry. The differences in their phase diagrams were rationalized based on the proposed molecular packing and relevant interfacial energies.
