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A series of non‐fullerene acceptors based on perylene monoimides coupled in the peri position through phenylene linkers were synthesized via Suzuki‐coupling reactions. Various substitution patterns were investigated using density functional theory (DFT) calculations in combination with experimental data to elucidate the geometry and their optical and electrochemical properties. Further investigations of the bulk properties with grazing incidence wide angle X‐ray scattering (GIWAXS) gave insight into the stacking behavior of the acceptor thin films. Electrochemical and morphological properties correlate with the photovoltaic performance of devices with the polymeric donor PBDB‐T and a maximum efficiency of 3.17 % was reached. The study gives detailed information about structure–property relationships of perylene‐linker‐perylene compounds. [ABSTRACT FROM AUTHOR]

The influence of N‐substituents on the photovoltaic properties of singly bay‐linked perylene diimides (diPDIs) was systematically investigated to understand the aromatic‐aliphatic balance, which is beneficial for achieving high device performance in organic photovoltaic (OPV) systems. The synthesis of various N‐substituted diPDIs was successfully achieved using a newly developed one‐step procedure, resulting in sufficiently high yields. Detailed investigations of seven variants of diPDIs demonstrated that the primary alkyl substituents, particularly the 2‐ethylhexyl group, induce the self‐organized growth of thin films with high crystallinity. This is beneficial for enhancing the device performance of bulk heterojunction (BHJ) systems. The results presented herein reveal the important roles of alkyl side chains as hydrophobic solubilizing auxiliaries or primary determinants in the control of the active layer nanomorphology. This offers a valuable guideline that is essential for developing high‐performance organic semiconductor materials for future practical applications. [ABSTRACT FROM AUTHOR]

One important feature of organic semiconductors is their solution processability, which allows researchers to tune their aggregation states in solution and solid states and to control the processing conditions to reach desirable electronic and optoelectronic properties. Temperature is one of the most important processing parameters of organic semiconductors and has been studied extensively particularly for those conjugated small‐ and macro‐ molecules with strong temperature‐dependent aggregation properties. This minireview summarizes the temperature‐induced aggregation behaviors of organic semiconductors in solution, during solution casting and upon thermal annealing post‐treatment of solid‐state thin films. The influences of different aggregation states on the optoelectronic properties, in particular the photovoltaic properties, are discussed. The conclusions in this work will provide a rational guide to precisely control the aggregation states of organic semiconductors to fabricate high‐performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

The packing mode of small‐molecular semiconductors in thin films is an important factor that controls the performance of their optoelectronic devices. Designing and changing the packing mode by molecular engineering is challenging. Three structurally related diketopyrrolopyrrole (DPP)‐based compounds were synthesized to study the effect of replacing C−C bonds by isoelectronic dipolar B←N bonds. By replacing one of the bridging C−C bonds on the peripheral fluorene units of the DPP molecules by a coordinative B←N bond and changing the B←N bond orientation, the optical absorption, fluorescence, and excited‐state lifetime of the compounds can be tuned. The substitution alters the preferential aggregation of the molecules in the solid state from H‐type (for C−C) to J‐type (for B←N). Introducing B←N bonds thus provides a subtle way of controlling the packing mode. The photovoltaic properties of the compounds were evaluated in bulk heterojunctions with a fullerene acceptor and showed moderate performance as a consequence of suboptimal morphologies, bimolecular recombination, and triplet‐state formation. Bond replacement: Introducing B←N bonds to replace C−C bonds and changing the B←N bond orientation provide a means to change the crystallization behavior, aggregation, energy levels, and solar‐cell performance of diketopyrrolopyrrole (DPP)‐based π‐conjugated compounds (see figure). [ABSTRACT FROM AUTHOR]

A series of three thiophene-naphthalene-based asymmetric oligomers-5-decyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (DtT), 5-decyl-5′′-(naphthalen-2-yl)-2,2′:5′,2′′-terthiophene (D3TN), and 5-(4-decylphenyl)-5′-(naphthalen-2-yl)-2,2′-bithiophene (DP2TN)-was synthesized by Suzuki cross-coupling reactions. The long alkyl side chains improved both the solubility of the oligomers in solvents and their tendency to self-assemble. UV/Vis absorption measurements suggested that DtT, D3TN, and DP2TN form H-type aggregates with a face-to-face packing structure. In addition, the three oligomers were found to adopt vertically aligned crystalline structures in films deposited on substrates, as revealed by grazing-incidence wide-angle X-ray scattering. These oligomers were used as the active layers of p-type organic field-effect transistors, and the resulting devices showed field-effect mobilities of 3.3×10−3 cm2 V−1 s−1 for DtT, 1.6×10−2 cm2 V−1 s−1 for D3TN, and 3.7×10−2 cm2 V−1 s−1 for DP2TN. The differences in transistor performances were attributed to the degree of π overlap and the morphological differences determined by the molecular structures. [ABSTRACT FROM AUTHOR]