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A thieno[3,4-b]thiophene-based electron acceptor, ATT-1, is designed and synthesized. ATT-1 exhibits a planar conjugated framework, broad absorption with a large absorption coefficient, and a slightly high LUMO energy level. Bulk-heterojunction (BHJ) solar cells based on PTB7-Th electron donor and ATT-1 electron acceptor delivered power conversion efficiencies of up to 10.07%, which is among the best performances reported for non-fullerene BHJ solar cells using PTB7-Th as the electron donor. [ABSTRACT FROM AUTHOR]

Thiophene-based materials have occupied a crucial position in the development of organic electronics. However, the energy band gaps of oligo- and polythiophenes are difficult to modulate without resorting to push -pull electronic effects. We describe herein a new series of monodisperse oligo (thieno [3,4- bjthiophene) derivatives with well-defined regioregular structures synthesized efficiently by direct C-H arylation. These compounds show a unique palette of colors and amphoteric redox properties with widely tunable energy band gaps. The capacity to stabilize both cations and anions results in both anodic and cathodic electrochromism. Under excitation, these compounds can produce photoionized states able to interconvert into neutral triplet or form these through singlet exciton fission or intersystem crossing. These features arise from a progressive increase in quinoidization on a fully planar platform making the largest effective conjugation length among hetero-oligomers. Oligo(thieno[3,4-b]thiophene)s might represent the more distinctive family of oligothiophenes of this decade. [ABSTRACT FROM AUTHOR]

Monodispersed conjugated oligothiophenes are receiving attention in fundamental and applied science due to their interesting optical, optoelectronic, and charge transport properties. These "low molecular weight" polymers serve as model structures for the corresponding polymer analogues, which are inherently polydispersed. Here we report the synthesis, electronic structure, molecular packing/morphology, and charge transport properties of monodispersed oligothiophenes with up to six didodecylquaterthiophene (DDQT) building block repeat units (i.e., 24 thiophene units). At the point where the effective conjugation length is reached, the electronic structure showed convergence behavior to the corresponding polymer, poly(3,3″-didodecyl-quaterthiophene) (PQT-12). X-ray crystal structure analysis of the dimer (DDQT-2) showed that terminal thiophenes exhibit syn-conformations, similar to the terminal syn-conformations observed in the trimer (DDQT-3). The dimer also exhibits a rare bending of the terminal alkyl side chains in order to prevent steric hindrance with neighboring hydrogens attached to core thiophenes. Grazing incidence X-ray scattering measurements revealed a morphology evolution from small molecule-like packing to polymer-like packing in thin films, with a morphology transition occurring near the effective conjugation length. Charge transport measurements showed a mobility increase with decreasing chain length. We correlated the molecular packing and morphology to charge transport and determined that carrier mobilities are most sensitive to crystallinity and crystal grain misorientation. This indicates that molecular weight is not a decisive factor for improved carrier mobility in the low molecular weight region, but rather the degree in crystallinity and in-plane crystal orientation. These results represent a fundamental advancement in understanding the relationship between conjugation length and carrier mobilities in oligothiophene semiconductors. [ABSTRACT FROM AUTHOR]

A series of acceptor--donor--acceptor simple oligomer-like small molecules based on oligothiophenes, namely, DRCN4T-DRCN9T, were designed and synthesized. Their optical, electrical, and thermal properties and photovoltaic performances were systematically investigated. Except for DRCN4T, excellent performances were obtained for DRCN5T-DRCN9T. The devices based on DRCN5T, DRCN7T, and DRCN9T with axisymmetric chemical structures exhibit much higher short-circuit current densities than those based on DRCN6T and DRCN8T with centrosymmetric chemical structures, which is attributed to their well-developed fibrillar network with a feature size less than 20 nm. The devices based on DRCN5T/PC71BM showed a notable certified power conversion efficiency (PCE) of 10.10% under AM 1.5G irradiation (100 mW cm-2) using a simple solution spin-coating fabrication process. This is the highest PCE for single-junction small-molecule-based organic photovoltaics (OPVs) reported to date. DRCN5T is a rather simpler molecule compared with all of the other high-performance molecules in OPVs to date, and this might highlight its advantage in the future possible commercialization of OPVs. These results demonstrate that a fine and balanced modification/design of chemical structure can make significant performance differences and that the performance of solution-processed small-molecule-based solar cells can be comparable to or even surpass that of their polymer counterparts. [ABSTRACT FROM AUTHOR]