The design of polymer acceptors plays an essential role in the performance of all‐polymer solar cells. Recently, the strategy of polymerized small molecules has achieved great success, but most polymers are synthesized from the mixed monomers, which seriously affects batch‐to‐batch reproducibility. Here, a method to separate γ‐Br‐IC or δ‐Br‐IC in gram scale and apply the strategy of monomer configurational control in which two isomeric polymeric acceptors (PBTIC‐γ‐2F2T and PBTIC‐δ‐2F2T) are produced is reported. As a comparison, PBTIC‐m‐2F2T from the mixed monomers is also synthesized. The γ‐position based polymer (PBTIC‐γ‐2F2T) shows good solubility and achieves the best power conversion efficiency of 14.34% with a high open‐circuit voltage of 0.95 V when blended with PM6, which is among the highest values recorded to date, while the δ‐position based isomer (PBTIC‐δ‐2F2T) is insoluble and cannot be processed after parallel polymerization. The mixed‐isomers based polymer, PBTIC‐m‐2F2T, shows better processing capability but has a low efficiency of 3.26%. Further investigation shows that precise control of configuration helps to improve the regularity of the polymer chain and reduce the π–π stacking distance. These results demonstrate that the configurational control affords a promising strategy to achieve high‐performance polymer acceptors.

Oligomeric acceptors are expected to combine the advantages of both highly developed small molecular and polymeric acceptors. However, organic solar cells (OSCs) based on oligomers lag far behind due to their slow development and low diversity. Here, three oligomeric acceptors were produced through oligomerization of small molecules. The dimer dBTICγ‐EH achieved the best power conversion efficiencies (PCEs) of 14.48 % in bulk heterojunction devices and possessed a T80 (80 % of the initial PCE) lifetime of 1020 h under illumination, which were far better than that of small molecular and polymeric acceptors. More excitingly, it showed PCEs of 16.06 % in quasi‐planar heterojunction (Q‐PHJ) devices which is the highest value OSCs using oligomeric acceptors to date. These results suggest that oligomerization of small molecules is a promising strategy to achieve OSCs with optimized performance between the high efficiency and durable stability, and offer oligomeric materials a bright future in commercial applications.

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In addition to efficiency, stability is another key factor in developing organic solar cells. The quasiplanar heterojunction (Q-PHJ) structure, combining two pure layers as major and tiny nanoscale bulk heterojunction (BHJ) at interface, demonstrates superior device stability compared with BHJ devices. In this contribution, the polymer donor, PBQx-H-TF, and configurationally defined polymeric acceptor, PBTIC-γ-TSe are synthesized and used to fabricate bilayer devices by orthogonal solvents, the corresponding Q-PHJ all-polymer solar cells (all-PSCs) deliver reliable stability with high efficiency. An encouraging PCE of 15.77% is achieved, which is the highest one among Q-PHJ all-PSCs with real-bilayer structure. There is a major improvement over the 13.91% PCE in the BHJ device, and the carrier transport performance is improved substantially following the reduction of recombination in the Q-PHJ all-PSCs. Benefiting from the bilayer morphology, the stability of Q-PHJ all-PSCs has been greatly enhanced over that of the BHJ devices. The charge recombination process is also more serious in the aging BHJ compared with the aging Q-PHJ all-PSCs. This work inspires the application of Q-PHJ in the preparation of high-efficient all-PSCs, but also provides guidance on the improvement of device stability from a dual approach of material and device engineering aspects.

The effect of isomerism in polymer donors is appealing as a means of optimization of molecular configurations in organic solar cells (OSCs) but has not been well explored. Two isomers, PAB-α and PAB-γ, with different orientations of their fused thiophene rings were designed and synthesized to investigate the influence of isomerism in polymer donors on their photovoltaic conversions. It was shown that two polymers with almost identical structures exhibited significant differences in the power conversion efficiency (PCE) of solar devices. The PAB-α-based devices achieve an excellent PCE of 15.05%, while the PAB-γ-based devices only obtain an extremely low PCE of 0.04%. Reasons for such a dramatic performance disparity include first, the absorption spectrum of PAB-γ being markedly blue-shifted and failing to match the absorption spectrum of common high-efficiency acceptors, such as Y6, and second, acceptor Y6 has preferable miscibility with PAB-α for a smaller χ value of 0.067 and smaller root-mean-square value of 0.98 nm. What is more, PAB-α has a closer π–π interaction distance compared to its isomer PAB-γ from grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis, and the order-of-magnitude difference between the hole and electron mobilities of two active layers also made the opposing values of their device efficiencies. Therefore, PAB-α has a superior performance in photovoltaic devices, demonstrating that fine tuning of atomic orientation could bring great changes to the properties of the polymer donors. This provides a new train of thought for the material design and evolution of device performance.

It is challenging yet appealing for researchers to construct new polymer donors that can work cooperatively with the polymer acceptors and thus realize maximum power conversion efficiencies (PCEs) of all-polymer solar cells (PSCs). We have synthesized two dithieno[3,2-f:2′,3′-h]quinoxaline-based wide band gap donor polymers (PBQx-Me-TF and PBQx-H-TF) and a new γ-position based narrow band gap polymer acceptor: PBTIC-γ-TT. The temperature-dependent absorption spectra showed that removal of a weaker electron-donating methyl group in the donor polymer strengthened the aggregation and the absorption coefficients. The crystal structures showed that PBQx-H-TF had a closer π−π stacking distance of 3.33 Å when compared to the PBQx-Me-TF (3.40 Å). The smaller E HOMO offset (0.07 eV) between the donor PBQx-H-TF and acceptor PBTIC-γ-TT than that of PBQx-Me-TF/PBTIC-γ-TT (0.10 eV) provided a better hole transport. The PBQx-H-TF/PBTIC-γ-TT films showed a smaller total energy loss (0.574 eV) than the PBQx-Me-TF/PBTIC-γ-TT film (0.607 eV); hence, this molecular structure adjustment reduced the nonradiative energy loss. PBQx-H-TF also showed better miscibility with PBTIC-γ-TT with a smaller χ value of 0.25. In addition, a bicontinuous interpenetrating microstructure was observed in the active layer blend film (PBQx-H-TF/PBTIC-γ-TT), resulting in a J SC of 22.24 mA cm −2 , a FF of 67.80%, and a PCE of 14.21% in the device. These observations revealed the significance of molecular structure adjustment for better device performance, and therefore, PBQx-H-TF can be an excellent candidate for all-PSCs.

NIR-II-emitting photosensitizers (PSs) have attracted great research interest due to their promising clinical applications in imaging-guided photodynamic therapy (PDT). However, it is still challenging to realize highly efficient PDT on NIR-II PSs. In this work, we develop a chlorination-mediated π-π organizing strategy to improve the PDT of a PS with conjugation-extended A-D-A architecture. The significant dipole moment of the carbon-chlorine bond and the strong intermolecular interactions of chlorine atoms bring on compact π-π stacking in the chlorine-substituted PS, which facilitates energy/charge transfer and promotes the photochemical reactions of PDT. Consequently, the resultant NIR-II emitting PS exhibits a leading PDT performance with a yield of reactive oxygen species higher than that of previously reported long-wavelength PSs. These findings will enlighten the future design of NIR-II emitting PSs with enhanced PDT efficiency.

Substitution of two-dimensional (2D) extended conjugation is considered to be an effective strategy to modify the optoelectronic properties of molecules, but the effects of these fused 2D-expansion are not clearly understood. Here, phenanthrene and acenaphthene were applied in A-DAD-A systems to study the impacts of different fused 2D-expansions. It was found that the aggregation behaviors in small molecules are quite different from those of polymer acceptors. The reasons can be explained by theoretical calculations with various configurations of monomers and dimers. This phenomenon leads to obvious diversities in morphologies in blend films, resulting in discrepancies with the performance of mobilities, exciton splitting, and bimolecular recombination in devices with the final organic solar cells (OSCs). The phenanthrene- and acenaphthene-based OSC devices, PTIC-HD-4Cl and PATIC-HD-Th, with appropriate aggregation states achieve superior power conversion efficiencies (PCEs) of 13.71% and 12.47%, while inferior PCEs of 7.29% and 6.57% are observed in OSC devices based on the ATIC-HD-4Cl and PPTIC-HD-Th with excessive aggregations. Our studies demonstrate that the packing arrangements of small molecules are quite different from that of polymer acceptors, and the fused 2D-expansion was found to be an effective strategy with which to adjust the aggregation behaviors for the design of high-crystallinity materials.