A new acceptor–donor–acceptor-structured nonfullerene acceptor, 2,2′-((2Z,2′Z)-(((4,4,9,9-tetrakis­(4-hexylphenyl)-4,9-dihydro-s-indaceno­[1,2-b:5,6-b′]­dithiophene-2,7-diyl)­bis­(4-((2-ethylhexyl)­oxy)­thiophene-4,3-diyl))­bis­(methanylylidene))­bis­(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))­dimalononitrile (i-IEICO-4F), is designed and synthesized via main-chain substituting position modification of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)­dimalononitrile. Unlike its planar analogue IEICO-4F with strong absorption in the near-infrared region, i-IEICO-4F exhibits a twisted main-chain configuration, resulting in 164 nm blue shifts and leading to complementary absorption with the wide-bandgap polymer (J52). A high solution molar extinction coefficient of 2.41 × 105 M–1 cm–1, and sufficiently high energy of charge-transfer excitons of 1.15 eV in a J52:i-IEICO-4F blend were observed, in comparison with those of 2.26 × 105 M–1 cm–1 and 1.08 eV for IEICO-4F. A power conversion efficiency of 13.18% with an open-circuit voltage (0.849 V), a short-circuit current density of 22.86 mA cm–2, and a fill factor of 67.9% were recorded in J52:i-IEICO-4F-based polymer solar cells (PSCs), demonstrating that this main-chain twisted strategy can be a guideline that facilitates the development of new acceptors to maximize the efficiency in PSCs.

Efficient charge generation is a prerequisite to achieve high power conversion efficiency (PCE) in organic/polymer solar cells (OSCs/PSCs), which involves photoinduced electron transfer and/or hole transfer between the donor/acceptor interface upon photoexcitation. A high yield of charge from both processes usually requires sufficient energy offset between the donor and acceptor for charge separation, fast transport, and extraction for charge collection, as well as significant absorption complementation to maximize photon harvest. Here we demonstrate highly efficient PSCs with efficient dual photocurrent generation pathways from a blend of a polymer donor and two narrow-bandgap nonfullerene acceptors, with an outstanding certified PCE of 13.0% (verified as 12.5%) in PSCs with single-junction device architecture. The devices from these material systems show nonradiative recombination loss of ∼0.22–0.24 V, one of the smallest values for OSCs achieved so far and comparable to those of solar cells based on monocrystalline Si or metal-halide perovskites. This study highlights that dual charge generation pathways with high yield and strongly reduced voltage loss are indispensable for further increasing the PCE of OSCs.

A new main-chain twisted small molecular acceptor with nonhalogenated end groups (i-IEICO) is designed and synthesized. In contrast to its planar analogue IECIO, i-IEICO possesses an obviously twisted backbone, leading to significant hypsochromic shift in film absorption, slight enhancement in solution extinction coefficient, and significantly elevated molecular energy level. Benefited from these features, i-IEICO is matched well with two wide band gap polymer donor materials (J52 and PBDB-T) both in absorption spectra and molecular energy levels. Relative to the planar-molecule IEICO-based devices, the open-circuit voltage (V OC ), short-circuit current density, and fill factor of the i-IEICObased devices are simultaneously improved, giving rising to a 10.48% (with J52) and 8.79% (with PBDB-T) power conversion efficiency, respectively. Moreover, J52:i-IEICO device exhibits a high V OC of 0.96 V accompanied by a small energy loss of 0.64 eV, which can be further improved to 1.01 V and 0.59 eV for the PBDB-T-based device. The obtained V OC of i-IEICO-based devices are among one of the highest values of either J52 or PBDB-T-based binary devices, suggesting the effectiveness of main-chain twisted strategy coupled with end-group modification to achieve highly efficient nonfullerene acceptors with low energy loss and high V OC .

Thioxopeptide bond psi[CS-N], a nearly isosteric modification of the native peptide bond, was introduced into insect kinin active core pentapeptide to evaluate the impact of backbone cis/trans photoswitching on bioactivity. The thioxo analog Phe(1)-Tyr(2)-psi[CS-N]-Pro(3)-Trp(4)-Gly(5)-NH(2) (psi[CS-N](2)-kinin), was synthesized by Fmoc solid-phase peptide strategy. The reversible photoswitching property was characterized via spectroscopic methods and HPLC, which showed that the cis conformer increased from 15.7 to 47.7% after 254 nm UV irradiation. A slow thermal reisomerization (t(1/2) = 40 min) permitted us to determine the cockroach hindgut myotropic activity of the thioxopeptide in the photostationary state. The results indicated that the activity increased significantly after UV irradiation and recovered to the ground level after thermal re-equilibration. In the present study, by utilizing the phototriggered isomerization in a specific position of peptide backbone, we revealed that the cis psi[CS-N](2)-kinin conformer is the active conformation when interacting with kinin receptor on cockroach hindgut.

Nonfullerene (NF) small molecular acceptors are very attractive for further improving the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) to overcome the limited absorptive region and fixed-energy-level drawbacks of fullerene-based electronic acceptors (PC61BM and PC71BM). The acceptor–donor–acceptor (A-D-A)-type oligomers (ITIC) containing an electron-rich core (four hexyl-phenyl-substituted indacenodithieno­[3,2-b]­thiophene) as a donor motif sealed with 2-(3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile as an acceptor motif has been intensively investigated, because of its excellent absorptive and photovoltaic properties. Side-chain modifications have been proven to be an effective approach to modulate the energy levels and absorptive behaviors of conjugated polymers, as well as conjugated small molecules. Through the introduction of various side-chain and end groups, a series of promisingly modified ITIC-based small molecules have been synthesized and well-studied. Herein, we reported three novel alkoxy-phenyl modified ITIC-type NF acceptors (namely, pO-ITIC, mO-ITIC, and FpO-ITIC), in which 4-hexyloxy-phenyl, 3-hexyloxy-phenyl, and 3-fluorine-4-hexyloxy-phenyl side-chains were connected on the indacenodithieno­[3,2-b]­thiophene core as the electron-donating segments of the A-D-A molecules. Both three small molecules exhibit good solubility in common solvents, finely tunable energy levels, and adjustable optical bandgaps. The 4-hexyloxy-phenyl and 3-hexyloxy-phenyl-substituted materials possess relatively low bandgaps (1.61 eV for pO-ITIC and 1.63 eV for mO-ITIC) and a 4.7% enhancement in the maximum extinction coefficient, compared to that of ITIC. As the result of the better absorption behaviors, inverted polymer solar cells based on pO-ITIC blended with PTB7-Th achieve an open-circuit voltage (V oc) of 0.80 V, a short-circuit current (J sc) of 14.79 mA/cm2, and a fill factor (FF) of 59.1%, leading to a high-power conversion efficiency (PCE) of 7.51%, relative to the 7.31% PCE of ITIC-based device. By using a new thiazolothiazole-based wide-bandgap polymer (PTZ-DO, 1.98 eV) with deep HOMO energy level (−5.43 eV) to match the optical absorption and molecular energy levels with the three NF acceptors, excellent PCE values9.28% for mO-ITIC and 9.03% for pO-ITICare obtained, which show increments of 15.3% and 12.2%, respectively, relative to that of ITIC (8.05%). This finding should offer useful guidelines for the design of novel NF acceptors for highly efficient PSCs through alkoxy-phenyl side-chains modified on the electron-donating moiety of A-D-A organic small molecules.