In this work, two asymmetric non-fullerene acceptors (NFAs), BTP-EHBO-4F and BTP-PHD-4F, are designed to be applied in green-solvent-processable organic photovoltaics (OPVs). BTP-EHBO-4F and BTP-PHD-4F show good solubilities in green solvent o-xylene. As a result, PM6:BTP-EHBO-4F-based devices exhibit outstanding photovoltaic performances using o-xylene as a solvent. By comparison, due to the poor solubility of Y6 in o-xylene, PM6:Y6-based devices show poor performances. Owing to the favorable phase separation, molecule packing, and orientation observed from atomic force microscopy (AFM) and grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements, PM6:BTP-PHD-4F-based devices demonstrate a PCE of 15.91% with a V OC of 0.87 V, a J SC of 25.64 mA/cm2, and an FF of 71.34%. Moreover, PM6:BTP-EHBO-4F-based devices exhibit an impressive PCE of 16.82% with a V OC of 0.85 V, a J SC of 26.12 mA/cm2, and an FF of 75.78%, which is outstanding for OPVs using o-xylene as a solvent.

The molecular design of wide-bandgap conjugated polymer donors (WB-CPDs) is a promising strategy for tuning the bulk heterojunction blend film morphologies to achieve high-performance organic photovoltaic (OPV) devices. Herein, we synthesize two WB-CPDs, namely, PBQ-H and PBQ-M, with and without methyl groups on the fused-dithieno­[3,2-f:2′,3′-h]­quinoxaline (DTQx) moiety. We systematically investigate their structure–property relationship and OPV performances. The AFM and 2D grazing-incidence wide-angle X-ray scattering (GIWAXS) studies reveal that the PBQ-H:BO-4Cl BHJ blend shows strengthened aggregation behavior and stronger π–π stacking on face-on orientation compared with the PBQ-M:BO-4Cl BHJ blend, enhancing the phase separation, charge transport, and fill factor (FF). Blend film absorption spectra, however, show that the PBQ-H:BO-4Cl BHJ blend exhibits a lower absorption coefficient than that of the PBQ-M:BO-4Cl BHJ blend, which decreases the short-circuit current density (J SC). As a consequence, the optimized PBQ-H:BO-4Cl BHJ blend delivers a higher power conversion efficiency (PCE) of 12.88% with a J SC of 23.97 mA/cm2, an open-circuit voltage (V OC) of 0.86 V, and an FF of 62.46%, compared with the PBQ-M:BO-4Cl BHJ blend (PCE of 11.81% with a J SC of 24.78 mA/cm2, a V OC of 0.85 V, and an FF of 56.11%). Overall, this work demonstrates that alkyl group substitution on the DTQx moiety on the basis of WB-CPDs is critical for controlling the film morphology and thus obtaining high OPV performances.

Molecular backbone modification, alkyl-chain engineering, and end-group functionalization are promising strategies for developing efficient high-performance non-fullerene acceptors (NFAs). Herein, two new NFAs, named TPQ-eC7-4F and TPQ-eC7-4Cl, are designed and synthesized. Both molecules have linear octyl chains on fused quinoxaline-containing heterocyclics as the central backbone and difluorinated (2F)/dichlorinated (2Cl) 1,1-dicyanomethylene-3-indanone (IC) as the end-group units. The influences of alkyl-chains on fused quinoxaline backbone and different halogenated end-groups on optical, electrochemical, and photovoltaic performances of organic solar cells (OSCs) are studied. In comparison with TPQ-eC7-4Cl, TPQ-eC7-4F exhibits blue-shifted absorptions with higher molar extinction coefficients in the film state as well as in the donor/acceptor (D/A) blend film state and up-shifting lowest unoccupied molecular orbital (LUMO) energy level. As a result, the OSC devices based on the PBDB-T:TPQ-eC7-4F display an outstanding power conversion efficiency (PCE) of 15.83% with a simultaneously increased open-circuit voltage (V oc) of 0.85 V, a short-circuit current-density (J sc) of 25.89 mA cm–2, and a fill factor (FF) of 72.20%, whereas the PBDB-T:TPQ-eC7-4Cl-based OSC device shows a decent PCE of 14.48% with a V oc of 0.84 V, a J sc of 24.56 mA/cm2, and an FF of 69.77%. To the best of our knowledge, this is the highest photovoltaic performance of PBDB-T-based single-junction binary-OSCs. In comparison, ascribed to the high crystallinity and low solubility of BTP-eC7-4Cl, the corresponding PBDB-T:BTP-eC7-4Cl-based OSC device shows poor photovoltaic performance (PCE of 11.87%). The experimental results demonstrate that fine-tuning the fused quinoxaline backbone with alkyl-chain and end-group functionalization are promising strategies to construct high-performance NFAs for PBDB-T-based single-junction binary-OSCs.

D18 and its derivatives (such as D18-Cl) newly emerged as high-performance conjugated polymers for bulk heterojunction (BHJ) solar cells, with efficiency breaching 17% when paired with small molecule acceptors such as Y6 and its derivatives. However, the complex synthesis of D18 series has limited their accessibility to the research community. We redesigned the original synthetic scheme of D18, particularly the key monomer, 5,8-bis(5-bromo-4-(2-butyl­octyl)thiophen-2-yl)­dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2-c][1,2,5]thiadiazole (Br2-T2-DTBT), and replaced a few key steps in the original scheme that were hard to reproduce and/or low yielding with simple to operate and high yielding reactions. Carother’s equation was successfully applied to control/tune the molar mass of D18-Cl, and three representative molar masses (high, medium, and low) of D18-Cl were subject to device testing. It is discovered that a medium molar mass (56 kg/mol) D18-Cl offered the highest performance (average 16.6%) when paired with Y6 as the acceptor in a typical BHJ device configuration, consistent with the literature report. This optimized synthesis of D18 series offers great synthetic tunability, and the modular nature/optimized key reactions will facilitate the design and synthesis of conjugated polymers for optoelectronics.

In high-performance bulk heterojunction organic solar cells (BHJ OSCs), cathode interlayers (CILs) have been effective in enhancing the device stability and photovoltaic performance by reducing the electron traps of ZnO layers. In this work, three water/alcohol-soluble conjugated polyelectrolytes (CPEs), P2T-CDTNa, PC-CDTNa, and PNDIT-FNa, as cathode interlayers (CILs) are reported. The effect of these three CPEs is validated by using PBDB-T:ITIC and PM6:Y6 as photoactive blends. Compared with ZnO-only devices, all three ZnO/CPE-based devices demonstrate enhanced photovoltaic performances. Especially, the ZnO/P2T-CDTNa-based devices show impressive power conversion efficiencies (PCEs) of 9.93% (V OC = 0.87 V, J SC = 16.56 mA/cm2, and FF = 69.04%) and 16.15% (V OC = 0.84 V, J SC = 27.71 mA/cm2, and FF = 69.60%) for PBDB-T:ITIC and PM6:Y6 BHJ photoactive blends, respectively.