In the past decade, the study on organic solar cells (OSCs) has made great progress. For commercial application, achieving high efficiency OSCs with the prominent stability is a crucial issue. Here, two crosslinkable vinyl-functionalized D–A–D–D₁-type polymers PM6-Ax (x: 5 or 15) were successfully synthesized by introducing a crosslinkable benzodithiophene (D₁) unit with vinyl functionality into the D–A polymer PM6. As expected, the un-crosslinked PM6-A5:Y6-based OSC process an outstanding PCE (15.20%) without additives, which is higher than that of the reference PM6:Y6-based OSCs (13.65%) by the D–A–D–D₁ strategy. It is found that polymers PM6-Ax can be crosslinked to some extent after annealing at 150 °C for a certain period of time. Meanwhile, by thermal crosslinking of the active layer, the PM6-Ax:Y6-based devices were fabricated and the stability was studied. Reference PM6:Y6-based devices were also fabricated. As a result, crosslinked PM6-A5:Y6-based devices retained 91.0% of the initial PCE under 48 h of continuous 60 °C thermal aging and 92.8% of the initial PCE under 72 h continuous white LED light illumination, whereas the reference PM6:Y6-based devices retained 81.9% and 72.7% under the same aging conditions. Moreover, crosslinked PM6-A5:Y6-based devices showed superior shelf-life stability over the reference devices. These results demonstrate that crosslinking of the PM6-A5:Y6-based active layer can significantly boost overall stability (including thermal-stability, photo-stability, and storage-stability) of the OSCs.

Four thiophene derivatives were prepared by replacing the 3,4 positions of thiophene by -OCH₃, -CH₃ -COOCH₃ and -CN, respectively. The polycondensations via direct arylation took place between the four thiophene derivatives and 2,7-dibromo-9,9-dioctylfluorene under six various catalytic conditions to investigate the substituent effects. The substituent can affect the electron cloud density of the active C-H bond, which can be monitored by the NMR chemical shift. The experimental results show that the reactivity decreases with increasing the chemical shift of active C-H bonds in the four thiophene derivatives, and thus can promote the direct arylation polycondensation. This phenomenon is explained by the electrophilic aromatic substitution (S_EAr) mechanism. UV-Visible absorption and photoluminescence were studied to investigate the substituent effect on optical properties of the four copolymers. The results show that these alternating fluorene-thiophene copolymers with different substituents are good fluorescent materials and promising in PLED applications.

We developed novel D–A–D–D₁-type polymers with unequal D and A units by incorporating a third component into the backbone of PM6 for enhanced short-circuit current density.

A series of novel praseodymium(Pr)-coordinated polymers with fluorene, phthalimide and bipyridine moieties in the main chain were synthesized via a coordination reaction and palladium-catalyzed Suzuki coupling polycondensation. Their structures, optical features and memory performance have been well studied. A resistive switching device with the configuration of ITO/polymer/Al was constructed using a spin-coating process. The device exhibits nonvolatile write-once-read-many-times (WORM) memory behavior. Based on the electrochemical properties and theoretical calculations of the polymers, the effects of the phthalimide moiety and neutral Pr complex on the polymer memory device performance were investigated. Our work offers valuable clues on the development of polymer memory devices.