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Fabricating solar cells with tandem structure is an efficient way to broaden the photon response range without further increasing the thermalization loss in the system. In this work, a tandem organic solar cell (TOSC) based on highly efficient nonfullerene acceptors (NFAs) with series connection type is demonstrated. To meet the different demands of front and rear sub-cells, two NFAs named F-M and NOBDT with a whole absorption range from 300 to 900 nm are designed, when blended with wide bandgap polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))] (PBDB-T) and narrow bandgap polymer PTB7-Th, respectively, the PBDB-T: F-M system exhibits a high V of 0.98 V and the PTB7-Th: NOBDT system shows a remarkable J of 19.16 mA cm , which demonstrate their potential in the TOSCs. With the guidance of optical simulation, by systematically optimizing the thickness of each layer in the TOSC, an outstanding power conversion efficiency of 14.11%, with a V of 1.71 V, a J of 11.72 mA cm , and a satisfactory fill factor of 0.70 is achieved; this result is one of the top efficiencies reported to date in the field of organic solar cells.

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Compared with inorganic photovoltaic technologies, flexibility is the most prominent feature of organic solar cells (OSCs). Flexible OSCs have been considered as one of the most promising directions in the OSC field, and have drawn tremendous attention in recent years. However, the power conversion efficiencies (PCEs) of flexible OSCs still lag behind those of their rigid counterparts. To further improve the performance of flexible OSCs, it is of great necessity for synergistic efforts to optimize flexible transparent electrodes (FTEs), photoactive materials, electrode buffer layers, and device structure engineering. Herein, the recent progress in flexible OSCs from the perspective of FTEs, including indium tin oxides, carbon nanomaterials, conducting polymers, silver nanowires, and ultrathin metal films and metal meshes, is summarized. In addition, the photoactive materials and electrode buffer layers in flexible OSCs are discussed to reveal the effects of material engineering and interface modification. Finally, a discussion of the future outlook and challenges of flexible OSCs is presented.

It is a great challenge to simultaneously improve the two tangled parameters, open circuit voltage (Voc) and short circuit current density (Jsc) for organic solar cells (OSCs). Herein, such a challenge is addressed by a synergistic approach using fine‐tuning molecular backbone and morphology control simultaneously by a simple yet effective side chain modulation on the backbone of an acceptor–donor–acceptor (A–D–A)‐type acceptor. With this, two terthieno[3,2‐b]thiophene (3TT) based A–D–A‐type acceptors, 3TT‐OCIC with backbone modulation and 3TT‐CIC without such modification, are designed and synthesized. Compared with the controlled molecule 3TT‐CIC, 3TT‐OCIC shows power conversion efficiency (PCE) of 13.13% with improved Voc of 0.69 V and Jsc of 27.58 mA cm−2, corresponding to PCE of 12.15% with Voc of 0.65 V and Jsc of 27.04 mA cm−2 for 3TT‐CIC–based device. Furthermore, with effective near infrared absorption, 3TT‐OCIC is used as the rear subcell acceptor in a tandem device and gave an excellent PCE of 15.72%.

Guided by a semi-empirical model, two small-molecule acceptors were rationally designed and an impressive PCE of 15.05% was achieved.

A new acceptor–donor–acceptor (A–D–A) type nonfullerene acceptor, 3TT‐FIC, which has three fused thieno[3,2‐b]thiophene as the central core and difluoro substituted indanone as the end groups, is designed and synthesized. 3TT‐FIC exhibits broad and strong absorption with extended onset absorption to 995 nm and a low optical bandgap of 1.25 eV. The binary device based on 3TT‐FIC and the polymer PTB7‐Th exhibits a power conversion efficiency (PCE) of 12.21% with a high short circuit current density (   J sc) of 25.89 mA cm−2. To fine‐tune the morphology and make full use of the visible region sunlight, phenyl‐C71‐butyricacid‐methyl ester (PC71BM) is used as the third component to fabricate ternary devices. In contrast to the binary devices, the ternary blend organic solar cells show significantly enhanced EQE ranging from 300 to 700 nm and thus an improved  J sc with a high value of 27.73 mA cm−2. A high PCE with a value of 13.54% is achieved for the ternary devices, which is one of the highest efficiencies in single junction organic solar cells reported to date. The results provide valuable insight for the ternary devices in which the external quantum efficiency (EQE) induced by the third component is evidently observed and directly contributed to the enhancement of the device efficiency.