In organic photovoltaics (OPVs) using nonfullerene acceptors, the fine-tuning of interfaces between donor and acceptor in the bulk-heterojunction (BHJ) structure has become an important factor to improve the performance. A series of electron-accepting π-conjugated compounds based on benzothiadiazole and arenedicarboximides were systematically synthesized to investigate the impact of structural modification on molecular orientation at donor−acceptor interfaces. X-ray diffraction and surface free energy measurements of these compounds in the film state revealed that the crystallinity correlates with the London dispersion (γ d ) and the polar components of their interfacial energies. BHJ solar cells prepared with our π-conjugated compounds as acceptors and poly(3-hexyl)thiophene as a donor exhibited that the structural modification exerts a significant influence on the photovoltaic characteristics, and afforded the highest power conversion efficiency of 2.05%. Absorption, photoluminescence, and carrier mobility measurements of the blend films showed that the OPV performance of our system are mainly governed by the efficiency of charge-separation into free carrier at the donor−acceptor interfaces. Furthermore, a strong correlation was found between the short-circuit current density of OPV and γ d of acceptors, indicating that this quantity promotes the formation of desirable charge-separated states. The findings provide novel information for the development of nonfullerene acceptors for OPVs.

Progressive advancement of remarkably high power conversion efficiencies (PCEs) of organic solar cells (OSCs) largely depends on the development of norfullerene acceptors (NFAs), revealing stupendous ability of OSCs to shift...

A series of new p-conjugated systems bearing arenedithiocarboxyimides (dithioimides) as electron-accepting terminal units were prepared utilizing thionation of the imide compounds in the final step of the synthesis.The thermal properties of the dithioimide compounds demonstrated that they had a weak crystallization nature, and their photophysical and electrochemical properties were significantly different from those of their imide analogs. As a result, the dithioimide compounds had narrower highest occupied molecular orbital (HOMO)lowest unoccupied molecular orbital (LUMO) energy gaps, and lower LUMO energy levels than those of the corresponding imide compounds. Organic field-effect transistors (OFETs) based on the dithioimide compounds showed good electron-transporting characteristics. Furthermore, the observed OFET performances were dramatically improved compared to those for the crystalline films of the corresponding imide derivatives, despite their tendency to form amorphous films. This unexpected phenomenon could be attributed to the presence of strong intermolecular electronic interactions for the dithioimide compounds, which induced the construction of a non-directional charge-transport pathway.Thus, the increase in electron mobilities for the dithioimide compounds was attributed to the combined effect of the low-lying LUMO energy level and the strong intermolecular electronic interactions in the solid state. Organic photovoltaics based on poly(3-hexylthiophene) as the hole-transporting material and the dithioimide compounds as the electron-transporting material exhibited poorer performances due to the high miscibility between the two compounds.

We revealed the relationship between the London dispersion components of three-dimensional non-fullerene acceptors and photocurrent generation efficiency in bulk-heterojunction-type organic photovoltaics.

Electron-donor function of methanofullerenes (MFs) in bulk heterojunction systems is demonstrated by the combination of MFs with the electron-transporting π-system that has a much higher electron affinity than MFs.