With the efficient synthesis of the crucial dibenzopyran building block, a series of PDBPTBT polymers containing different alkyl side chains and/or fluorine substitution were designed and synthesized via the microwave-assisted Suzuki polycondensation. Quantum chemistry calculations based on density functional theory indicated that different substitutions have significant impacts on the planarity and rigidity of the polymer backbones. Interestingly, the alkyloxy chains of PDBPTBT-4 tend to stay in the same plane with the benzothiadiazole unit, but the others appear to be out of plane. With the S···O and F···H/F···S supramolecular interactions, the conformations of the four polymers will be locked in different ways as predicted by the quantum chemistry calculation. Such structural variation resulted in varied solid stacking and photophysical properties as well as the final photovoltaic performances. Conventional devices based on these four polymers were fabricated, and PDBPTBT-5 displayed the best PCE of 5.32%. After optimization of the additive types, ratios, and the interlayers at the cathode, a high PCE of 7.06% (V = 0.96 V, J = 11.09 mA/cm, and FF = 0.67) is obtained for PDBPTBT-5 with 2.0% DIO as the additive and PFN-OX as the electron-transporting layer. These results indicated DBP-based conjugated polymers are promising wide band gap polymer donors for high-efficiency polymer solar cells.

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Molecular electronic structure plays a vital role in the photovoltaic performances in polymer solar cells (PSCs) due to their influences on light-harvesting, charge carrier transfer, π–π stacking, etc. Indacenodithiophene as a star unit has been well studied in PSCs; various structural derivation methods have been tried, but they are still not efficient in improvement of power conversion efficiencies (PCE) due to the narrow optical absorptions. In this contribution, a novel planar DMIDT with extended lateral π-electron delocalization is efficiently synthesized via introduction of sp2 hybrid carbons as the bridge atoms. Based on this novel building block, a two-dimensional conjugated polymer PDMIDT-TPD is prepared, and the unique structure improves the conjugation at the lateral direction, enlarges the electron delocalization area, and greatly broadens the absorption spectrum with a full coverage from 350 to 700 nm. Finally, a PCE of 8.26% is achieved when blended with PC71BM, which is the highest result among the IDT-based polymer donors. Meanwhile, PDMIDT-TPD also presents good compatibility with the non-fullerene acceptor, and a preliminary PCE of 6.88% is obtained. In all, this work not only provides an excellent donor material but also offers a general and simple derivation strategy for fused aromatic building blocks.

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A new centrosymmetrical dipyran unit (DTDP) is successfully prepared by means of an efficient and universal way, and a series of PDTDP polymers have been prepared so as to assess their potential application in organic photovoltaic. The function of pyran moiety is not merely limited to tune the electron-donating roles and energy levels but it also contributes to solubility improvement. Interestingly, all pyran-based polymers displayed wide absorption ranging from 350 to 780 nm, but varied aggregation phenomena are observed. Furthermore, the quantum chemistry calculations for dimers, morphology study and grazing-incidence wide-angle X-ray scattering analysis for blend films have been utilized to understand the variations at photovoltaic performances. Finally, PDTDP-4 achieved the highest power conversion efficiency of 7.26% ( V = 0.72 V, FF = 0.66, and J = 15.30 mA/cm), demonstrating promising usage for high-efficiency polymer donors in polymer solar cells. In all, not only a promising dipyran building block is provided by this study, more dipyran derivatives and polymers could be prepared via this facile synthetic route.