No abstract

We report the synthesis of a family of multifluorine substituted oligomers and the corresponding polymer that have the same backbones but different conjugation lengths and amounts of fluorine atoms on the backbone. The physical properties and photovoltaic performances of these materials were systematically investigated using optical absorption, charge mobility, atomic force microscopy, transmission electron microscopy, grazing incidence X-ray diffraction, resonant soft X-ray scattering methods, and photovoltaic devices. The power conversion efficiencies (PCEs) based on oligomers were much higher than that in the polymer. Moreover, the devices based on BIT6F and BIT10F, which have an axisymmetric electron-deficient difluorobenzothiadiazole as the central unit, gave slightly higher PCEs than those with centrosymmetric electron-rich indacenodithiophene (IDT) as the central unit (BIT4F or BIT8F). Using proper solvent vapor annealing (SVA), particularly using thermal annealing (TA) followed by SVA, the device performance could be significantly improved. Notably, the best PCE of 9.1% with a very high FF of 0.76 was achieved using the medium-sized oligomer BIT6F with the optimized film morphology. This efficiency is the highest value reported for organic solar cells from small-molecules without rhodanine terminal group. More excitingly, devices from the shortest oligomer BIT4F showed an impressively high FF of 0.77 (the highest FF value reported for solution-processed small-molecule organic solar cells). These results indicate that photovoltaic performances of oligomers can be modulated through successive change in chain-length and fluorine atoms, alternating spatial symmetric core, and combined post-treatments.

A fused-ring electron acceptor Y6 was used to fabricate single-crystal organic field-effect transistors, providing high ambipolar mobilities.

Designing highly efficient and durable electrocatalysts that accelerate sluggish oxygen reduction reaction kinetics for fuel cells and metal–air batteries are highly desirable but challenging. Herein, a facile yet robust strategy is reported to rationally design single iron active centers synergized with local S atoms in metal–organic frameworks derived from hierarchically porous carbon nanorods (Fe/N,S‐HC). The cooperative trithiocyanuric acid‐based coating not only introduces S atoms that regulate the coordination environment of the active centers, but also facilitates the formation of a hierarchically porous structure. Benefiting from electronic modulation and architectural functionality, Fe/N,S‐HC catalyst shows markedly enhanced ORR performance with a half‐wave potential (E1/2) of 0.912 V and satisfactory long‐term durability in alkaline medium, outperforming those of commercial Pt/C. Impressively, Fe/N,S‐HC‐based Zn–air battery also presents outstanding battery performance and long‐term stability. Both electrochemical experimental and density functional theoretical (DFT) calculated results suggest that the FeN4 sites tailored with local S atoms are favorable for the adsorption/desorption of oxygen intermediate, resulting in lower activation energy barrier and ultraefficient oxygen reduction catalytic activity. This work provides an atomic‐level combined with porous morphological‐level insights into oxygen reduction catalytic property, promoting rational design and development of novel highly efficient single‐atom catalysts for the renewable energy applications.