A Wide-Bandgap Conjugated Polymer Based on Quinoxalino[6,5-f ]quinoxaline for Fullerene and Non-Fullerene Polymer Solar Cells

Non-Covalent Interactions between Polyvinyl Chloride and Conjugated Polymers Enable Excellent Mechanical Properties and High Stability in Organic Solar Cells

The incorporation of insulating polymers into conjugated polymers has been widely explored as a strategy to improve mechanical properties of flexible organic electronics. However, phase separation due to the immiscibility of these polymers has limited their effectiveness. In this study, we report the discovery of multiple non-covalent interactions that enhances the miscibility between insulating and conjugated polymers, resulting in improved mechanical properties. Specifically, we have added polyvinyl chloride (PVC) into the conjugated polymer PM6 and observed a significant increase in solution viscosity, indicative of favorable miscibility between these two polymers. This phenomenon has been rarely observed in other insulating/conjugated polymer composites. Thin films of PM6/PVC exhibit a much-improved crack-onset strain of 19.35 %, compared to 10.12 % for pristine PM6 films. Analysis reveal that a "cyclohexyl-like" structure formed through dipole-dipole interactions and hydrogen bonding between PVC and PM6 acted as a cross-linking site in the thin films, leading to improved mechanical properties. Moreover, PM6/PVC blend films have demonstrated excellent thermal and bending stability when applied as an electron donor in organic solar cells. These findings provide new insights into non-covalent interactions that can be utilized to enhance the properties of conjugated polymers and may have potential applications in flexible organic electronics.

Enhanced photothermal therapy performance of D-A conjugated polymers based on [1,2,3]triazolo[4,5-g]quinoxaline by manipulating molecular motion

Donor-acceptor (D-A) conjugated polymers can favor the nonradiative thermal dissipation process, due to the formation of an intramolecular charge transfer (ICT) state resulting from the electron cloud delocalization of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital). Thus, to realize a high extinction coefficient and excellent photothermal conversion ability for a single photothermal agent, donor-acceptor type conjugated polymers PBDT-QTz and PCDT-QTz, comprising a new electron-deficient unit 2-(2-decyltetradecyl)-6,7-dimethyl-2H-[1,2,3]triazolo [4,5-g] quinoxaline (QTz) as the acceptor and 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (BDT) or 4H-cyclopenta[2,1-b:3,4-b'] dithiophene (CDT) as the donor, are designed and synthesized by manipulating intramolecular motion. The high extinction coefficient of 28.5 L g-1 cm-1 at 850 nm and the optimal photothermal conversion efficiency of 64.3% under an 808 nm laser are achieved based on PBDT-QTz. Consequently, PBDT-QTz nanoparticles can be successfully used for both in vitro and in vivo experiments. After intravenous administration and 808 nm laser irradiation, HeLa tumor-bearing mice achieve complete tumor remission without recurrence. The results provide an efficient photothermal agent by manipulating molecular motion.

Quinoxaline-Based D-A Copolymers for the Applications as Polymer Donor and Hole Transport Material in Polymer/Perovskite Solar Cells

Polymer solar cells (PSCs) have achieved great progress recently, benefiting from the rapid development of narrow bandgap small molecule acceptors and wide bandgap conjugated polymer donors. Among the polymer donors, the D-A copolymers with quinoxaline (Qx) as A-unit have received increasing attention since the report of the low-cost and high-performance D-A copolymer donor based on thiophene D-unit and difluoro-quinoxalline A-unit in 2018. In addition, the weak electron-deficient characteristic and the multiple substitution positions of the Qx unit make it an ideal A-unit in constructing the wide bandgap polymer donors with different functional substitutions. In this review article, recent developments of the Qx-based D-A copolymer donors, including synthetic method of the Qx unit, backbone modulation, side chain optimization, and functional substitution of the Qx-based D-A copolymers, are summarized and discussed. Furthermore, the application of the Qx-based D-A copolymers as hole transport material in perovskite solar cells (pero-SCs) is also introduced. The focus mainly on the molecular design strategies and structure-properties relationship of the Qx-based D-A copolymers, aiming to provide a guideline for developing high-performance Qx-based D-A copolymers for the applications as donor in PSCs and as hole transport material in pero-SCs.

Fine Tuning Alkyl Substituents on Dithienoquinoxaline-Based Wide-Bandgap Polymer Donors for Organic Photovoltaics

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.