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The employment of an intrinsic quinoidal building block, benzodipyrrolidone (BDP), on constructing conjugated polymers (PBDP-2F and PBDP-2CN) with high electron mobility and unipolar transport characteristic in polyethylenimine ethoxylated (PEIE) modified organic field-effect transistors (OFETs) is reported. The intrinsic quinoidal characteristic and excellent co-planarity of BDP can lower the lowest unoccupied molecular orbital (LUMO) levels and improve ordered interchain packing of the resulting polymers in solid states, which are favorable for electron-injection and transport. By using PEIE as the interlayer to block the hole injection, unipolar n-type transport characteristics with high electron mobility of 0.58 and 1.01 cm2 V−1 s−1 were achieved by the OFETs based on PBDP-2F and PBDP-2CN, respectively. More importantly, the extracted mobilities are highly reliable with the reliability factor of above 80%. To the best of our knowledge, PBDP-2CN is the very first quinoid-based conjugated polymer with reliable electron mobility exceeding 1 cm2 V−1 s−1. This work represents a significant step in exploring intrinsic quinoidal CPs for application in n channel OFETs and logic complementary circuits.

Polythiophenes, with merits of low cost and high scalability of synthesis, have received growing interest in organic solar cells. To date, the best-performing polythiophene:nonfullerene solar cells exhibit typical power conversion efficiencies (PCEs) of 10%–12%, which is much lower than those employing PM6- and D18-type polymers. This inferior performance is mostly limited by the improper miscibility between polythiophene and acceptors. Efforts on engineering the molecular structure to systematically tune the miscibility are required. With the aid of group contribution calculations, the miscibility of polythiophene:nonfullerene blend system was finely tuned by varying the ratios of siloxane-terminated chains and alkyl chains in ester-substituted polythiophenes through random copolymerization. Based on a series of the polythiophene and nonfullerene acceptors, the detailed analysis of blend miscibility and performance reveals a surprising anticorrelation between the Flory-Huggins interaction parameter ( χ aa) and the optimal time of solvent vapor annealing for device performance across these systems. Primarily due to the slightly higher χ aa, the blend of PDCBT-Cl-Si5 and ITIC-Th1 results in a record-high PCE of 12.85% in polythiophene:nonfullerene solar cells. The results not only provide a calculation-guided approach for molecular design but also prove that precise control of the miscibility is an effective way to design high-performance polythiophene:nonfullerene blends and beyond.

Active layer morphology is a key factor that dictates the device performance and stability of polymer solar cells (PSCs). Herein, we investigate the morphology evolution of the active layer and the impacts on device performance and stability upon varying the molecular weights of polymer donor (PBDB-T4Cl5S) from 17 to 98 kg mol−1. When blended with a leading non-fullerene acceptor (Y6), both the short-circuit current density and fill factor of the PSCs rise gradually with increasing the polymer molecular weights. Detailed morphology analysis showed that the reduced phase separation scale and improved phase purity accounted for these enhancements. Interestingly, the best device stability was achieved by the polymer with a medium molecular weight of 30 kg mol−1, which is most likely caused by the nearly-optimal miscibility between the polymer donor and Y6. These results demonstrate that the optimization of molecular weights of polymer donors is crucial to achieve high-efficiency and high-stability simultaneously for non-fullerene PSCs.

Due to the simple structure and excellent scalability, regioregular poly(3-hexylthiophene) (P3HT) has become much more popular as a low-cost donor polymer partner with the emerging nonfullerene acceptors in recent years. Presently, the application and the molar mass dependence of direct arylation polycondensation (DArP) prepared P3HT in fullerene-free organic solar cells have not been explored yet. In this work, five batches of P3HT with weight-average molar mass ranging from 8.9 kg mol−1 to 89.1 kg mol−1 were successfully prepared via DArP, with the aim to detail the interaction–performance relationships in the state-of-the-art P3HT:nonfullerene photovoltaic blend, namely P3HT:ZY-4Cl. Our thermodynamic analysis revealed that the amorphous–amorphous interaction parameters strongly depend on the P3HT molar mass and can be varied by a factor of 2.75. Owing to the best π–π stacking order deduced from grazing incidence X-ray diffraction and the smallest domain size, the blend based on the medium molar mass batch (25.5 kg mol−1) delivered the highest current density, fill factor, and power conversion efficiency up to ∼10% among the five systems. Our study confirmed that DArP is an effective protocol for the synthesis of P3HT for efficient non-fullerene polymer solar cells and the established relationships can be applied to screen the best batch for P3HT-based organic photovoltaics.

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) based on non-fullerene acceptors are still limited by large energy loss (ΔEloss). Herein, we report an easy and feasible way to reduce the ΔEloss, specifically the energy losses caused by non-radiative recombination of OSCs via introducing 3,4-dicyanothiophene (DCT), a structurally simple building block with strong electron-withdrawing ability, into a state-of-the-art donor polymer PBDB-TF to form ternary copolymers. The effects of DCT content in the ternary copolymers on the optical properties, energy levels, film morphology, charge transport, photovoltaic performance, and energy losses are studied comprehensively. Significant efficiency improvement in OSCs has been achieved by the DCT-based ternary copolymers as compared to the benchmark polymer PBDB-TF mainly because of a higher open-circuit voltage enabled by the reduced non-radiative recombination energy loss. A high PCE of 16.6% and a low non-radiative recombination energy loss (0.22 eV) were achieved in ternary OSCs with the DCT-based terpolymer as the electron donor and Y6-BO and PC71BM as the electron acceptors.

Summary Polythiophene (PT) and its derivatives have attracted long-standing attention in the organic photovoltaic community for their low cost and high scalability of synthesis. However, due to the lack of rational guidelines in controlling morphology and matching materials, the power conversion efficiencies (PCEs) based on PTs reported so far are generally below 10%. Here, we establish the first-ever relationship between miscibility, morphology, and device performance of binary blends, based on various nonfullerene acceptors (ITIC-Th1, ITIC, IT4F, IDIC, and Y6) and a PT derivative named PDCBT-Cl by scattering and calorimetric characterizations. Benefiting from a properly quenched mixed phase, PDCBT-Cl:ITIC-Th1 system shows the best efficiency of over 12%. Conversely, the blend of PDCBT-Cl and the star acceptor Y6 remained in a homogeneous state due to their high miscibility, resulting in abysmal performance with PCE of 0.5%. Specific guidelines are also proposed to remediate the performance of PDCBT-Cl:Y6, which are crucial for advancing their practical applications.

Understanding the key factors influencing the mechanical and electrical properties of semiconducting polymers is crucial to the development of stretchable electronics. In this work, a high-mobility...

An A2B2 type monomer, 1,6-bis(4-formylphenyl)-3,8-bis(4-aminophenyl)pyrene (BFBAPy), was employed for the fabrication of continuous and highly crystalline 2D imine-linked covalent organic framework (COF) films with tunable thickness via interfacial self-polymerization. These films served as stable acidichromism sensors with rapid response, low detection limit and good repeatability.

Top-performance organic solar cells (OSCs) consisting of conjugated polymer donors and nonfullerene small molecule acceptors (NF-SMAs) deliver rapid increases in efficiencies. Nevertheless, many of the polymer donors exhibit high stiffness and small molecule acceptors are very brittle, which limit their applications in wearable devices. Here, a simple and effective strategy is reported to improve the stretchability and reduce the stiffness of high-efficiency polymer:NF-SMA blends and simultaneously maintain the high efficiency by incorporating a low-cost commercial thermoplastic elastomer, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS). The microstructure, mechanical properties, and photovoltaic performance of PM6:N3 with varied SEBS contents and the molecular weight dependence of SEBS on microstructure and mechanical properties are thoroughly characterized. This strategy for mechanical performance improvement exhibits excellent applicability in some other OSC blend systems, e.g., PBQx-TF:eC9-2Cl and PBDB-T:ITIC. More crucially, the elastic modulus of such complex ternary blends can be nicely predicted by a mechanical model. Therefore, incorporating thermoplastic elastomers is a widely applicable and cost-effective strategy to improve mechanical properties of nonfullerene OSCs and beyond.

Regulating molecular structure to optimize the active layer morphology is of considerable significance for improving the power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, we demonstrated a simple ternary copolymerization approach to develop a terpolymer donor PM6-Tz20 by incorporating the 5,5'-dithienyl-2,2'-bithiazole (DTBTz, 20 mol%) unit into the backbone of PM6 (PM6-Tz00). This method can effectively tailor the molecular orientation and aggregation of the polymer, and then optimize the active layer morphology and the corresponding physical processes of devices, ultimately boosting FF and then PCE. Hence, the PM6-Tz20: Y6-based OSCs achieved a PCE of up to 17.1% with a significantly enhanced FF of 0.77. Using Ag (220 nm) instead of Al (100 nm) as cathode, the champion PCE was further improved to 17.6%. This work provides a simple and effective molecular design strategy to optimize the active layer morphology of OSCs for improving photovoltaic performance.