A-A Strategy Enables Desirable Performance of All-Polymer Solar Cells Fabricated with Nonhalogenated Solvents

Green-Solvent-Processed All-Polymer Solar Cells with Enhanced Efficiency and Stability through Molecular Design and Side-Chain Engineering

Green-solvent-processed all-polymer solar cells (AP-SCs) are regarded as an excellent candidate for renewable energy due to their better stability and eco-friendly features. Two polymers, PYF-U and PYF-BO, have been designed by introducing a Y-series derivative with difluoro-substituted dicyanindenone units and a difluorobenzotriazole derivative as the first and second electron-deficient (A) units, respectively. The introduction of two additional F atoms on dicyanindenone units leads to a more coplanar backbone because of noncovalent interactions. Compared with the polymer PYF-U with undecyl chains on thiophene, the polymer PYF-BO with 2-butyloctyl chains exhibits stronger intermolecular aggregation during the film-forming process, more dominant face-on molecular packing, and higher crystallinity in films. Therefore, the PM6:PYF-BO AP-SC achieves an efficiency of 15.38%, outperforming that of the PM6:PYF-U device (14.27%). Moreover, the former exhibits a longer T80 lifetime (1789 h) than the latter (826 h) under thermal aging at 65 °C because of better molecular packing and morphology. Our research demonstrates that combining noncovalent interactions to enhance the coplanarity of the polymeric backbone with side-chain engineering to optimize molecular packing and blend-film morphology is one of the efficient strategies for developing high-performance polymer acceptors.

The Double-Cross of Benzotriazole-Based Polymers as Donors and Acceptors in Non-Fullerene Organic Solar Cells

Organic solar cells (OSCs) are considered a very promising technology to convert solar energy to electricity and a feasible option for the energy market because of the advantages of light weight, flexibility, and roll-to-roll manufacturing. They are mainly characterized by a bulk heterojunction structure where a polymer donor is blended with an electron acceptor. Their performance is highly affected by the design of donor-acceptor conjugated polymers and the choice of suitable acceptor. In particular, benzotriazole, a typical electron-deficient penta-heterocycle, has been combined with various donors to provide wide bandgap donor polymers, which have received a great deal of attention with the development of non-fullerene acceptors (NFAs) because of their suitable matching to provide devices with relevant power conversion efficiency (PCE). Moreover, different benzotriazole-based polymers are gaining more and more interest because they are considered promising acceptors in OSCs. Since the development of a suitable method to choose generally a donor/acceptor material is a challenging issue, this review is meant to be useful especially for organic chemical scientists to understand all the progress achieved with benzotriazole-based polymers used as donors with NFAs and as acceptors with different donors in OSCs, in particular referring to the PCE.

Noncovalent Interaction Boosts Performance and Stability of Organic Solar Cells Based on Giant-Molecule Acceptors

Designing giant-molecule acceptors is deemed as an up-and-coming strategy to construct stable organic solar cells (OSCs) with high performance. Herein, two giant dimeric acceptors, namely, DYV and DYFV, have been designed and synthesized by linking two Y-series derivatives with a vinyl unit. DYFV exhibits more red-shifted absorption, down-shifted energy levels, and enhanced intermolecular packing than DYV because the intramolecular noncovalent interaction (H···F) of DYFV leads to better coplanarity of the backbone. The D18:DYFV film owns a distinct nanofibrous nanophase separation structure, a more dominant face-on orientation, and more balanced carrier mobilities. Therefore, the D18:DYFV OSC achieves a higher photoelectron conversion efficiency of 17.88% and a longer-term stability with a t80 over 45,000 h compared with the D18:DYV device. The study demonstrates that the intramolecular noncovalent interaction is a superior strategy to design giant-molecule acceptors and boost the photovoltaic performance and stability of the OSCs.