The quest for sustainable energy sources has led to accelerated growth in research of organic solar cells (OSCs). A solution‐processed bulk‐heterojunction (BHJ) OSC generally contains a donor and expensive fullerene acceptors (FAs). The last 20 years have been devoted by the OSC community to developing donor materials, specifically low bandgap polymers, to complement FAs in BHJs. The current improvement from ≈2.5% in 2013 to 17.3% in 2018 in OSC performance is primarily credited to novel nonfullerene acceptors (NFA), especially fused ring electron acceptors (FREAs). FREAs offer unique advantages over FAs, like broad absorption of solar radiation, and they can be extensively chemically manipulated to tune optoelectronic and morphological properties. Herein, the current status in FREA‐based OSCs is summarized, such as design strategies for both wide and narrow bandgap FREAs for BHJ, all‐small‐molecule OSCs, semi‐transparent OSC, ternary, and tandem solar cells. The photovoltaics parameters for FREAs are summarized and discussed. The focus is on the various FREA structures and their role in optical and morphological tuning. Besides, the advantages and drawbacks of both FAs and NFAs are discussed. Finally, an outlook in the field of FREA‐OSCs for future material design and challenges ahead is provided.

A series of diaryl‐substituted perylene bis(imides) (PBIs) containing electron‐donating and ‐withdrawing aryl groups in the bay region (1‐, 6‐, 7‐ and/or 12‐positions of the perylene core) were synthesized by Suzuki coupling reaction. The corresponding regioisomers, namely, 1,7‐ and 1,6‐regioisomer, were separated from the mixture by conventional column chromatography without any need of recrystallization. All the individual regioisomers were fully characterized by 1H NMR and HRMS spectroscopy. The compounds were studied by optical spectroscopy and electrochemical techniques. The optical and electrochemical properties of 1,7‐regioisomer are slightly different from the 1,6‐regioisomer of the respective diaryl‐PBI. Significant redshift and broadening of the absorption and emission maxima were observed in all synthesized PBIs depending upon the electronic nature of the attached aryl group. This is very first time such large series of 1,6‐diarylperylenetetracarboxydiimides with their corresponding 1,7‐regioisomers were synthesized, separated, characterized and studied in detail.

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We report the synthesis and characterization of four novel small bandgap copolymers incorporating the electron-deficient thieno­[2,3-d:5,4-d′]­bisthiazole and selenopheno­[2,3-d:5,4-d′]­bisthiazole building blocks with a series of electron-deficient diketopyrrolopyrole units. The four resultant copolymers were synthesized via palladium Stille cross-coupling reaction, and their optical, thermal stability, electrochemical, and field-effect charge transport properties were investigated. All copolymers showed low optical bandgaps (1.53–1.56 eV); in addition, X-ray diffraction on solution-cast films revealed that the selenium-containing copolymers exhibit higher crystallinity compared to their thiophene counterparts.