Improving the Intrinsic Stretchability of Fully Conjugated Polymer for Deep-Blue Polymer Light-Emitting Diodes with a Narrow Band Emission: Benefits of Self-Toughness Effect

Elastic-Plastic Fully π-Conjugated Polymer with Excellent Energy Dissipation Capacity for Ultra-Deep-Blue Flexible Polymer Light-Emitting Diodes with CIEy = 0.04

Emerging intrinsically flexible fully π-conjugated polymers (FπCPs) are a promising functional material for flexible optoelectronics, attributed to their potential interchain interpenetration and entanglement. However, the challenge remains in obtaining elastic-plastic FπCPs with intrinsic robust optoelectronic property and excellent long-term and cycling deformation stability simultaneously for applications in deep-blue flexible polymer light-emitting diodes (PLEDs). This study, demonstrates a series of elastic-plastic FπCPs (P1-P4) with an excellent energy dissipation capacity via side-chain internal plasticization for the ultra-deep-blue flexible PLEDs. First, the freestanding P1 film exhibited a maximum fracture strain of 34.6%. More interestingly, the elastic behavior is observed with a low strain (≤10%), and the stretched film with a high deformation (>10%) attributed to plastic processing revealed the robust capacity to realize energy absorption and release. The elastic-plastic P1 film exhibits outstanding ultra-deep-blue emission, with an efficiency of 56.38%. Subsequently, efficient PLEDs are fabricated with an ultra-deep-blue emission of CIE (0.16, 0.04) and a maximum external quantum efficiency of 1.73%. Finally, stable and efficient ultra-deep-blue electroluminescence are obtained from PLEDs based on stretchable films with different strains and cycling deformations, suggesting excellent elastic-plastic behavior and deformation stability for flexible electronics.

A Holistic Review of C = C Crosslinkable Conjugated Molecules in Solution-Processed Organic Electronics: Insights into Stability, Processibility, and Mechanical Properties

Solution-processable organic conjugated molecules (OCMs) consist of a series of aromatic units linked by σ-bonds, which present a relatively freedom intramolecular motion and intermolecular re-arrangement under external stimulation. The cross-linked strategy provides an effective platform to obtain OCMs network, which allows for outstanding optoelectronic, excellent physicochemical properties, and substantial improvement in device fabrication. An unsaturated double carbon-carbon bond (C = C) is universal segment to construct crosslinkable OCMs. In this review, the authors will set C = C cross-linkable units as an example to summarize the development of cross-linkable OCMs for solution-processable optoelectronic applications. First, this review provides a comprehensive overview of the distinctive chemical, physical, and optoelectronic properties arising from the cross-linking strategies employed in OCMs. Second, the methods for probing the C = C cross-linking reaction are also emphasized based on the perturbations of chemical structure and physicochemical property. Third, a series of model C = C cross-linkable units, including styrene, trifluoroethylene, and unsaturated acid ester, are further discussed to design and prepare novel OCMs. Furthermore, a concise overview of the optoelectronic applications associated with this approach is presented, including light-emitting diodes (LEDs), solar cells (SCs), and field-effect transistors (FETs). Lastly, the authors offer a concluding perspective and outlook for the improvement of OCMs and their optoelectronic application via the cross-linking strategy.

Control of Properties through Hydrogen Bonding Interactions in Conjugated Polymers

Molecular design is crucial for endowing conjugated polymers (CPs) with unique properties and enhanced electronic performance. Introducing Hydrogen-bonding (H-bonding) into CPs has been a broadly exploited, yet still emerging strategy capable of tuning a range of properties encompassing solubility, crystallinity, electronic properties, solid-state morphology, and stability, as well as mechanical properties and self-healing properties. Different H-bonding groups can be utilized to tailor CPs properties based on the applications of interest. This review provides an overview of classes of H-bonding CPs (assorted by the different H-bond functional groups), the synthetic methods to introduce the corresponding H-bond functional groups and the impact of H-bonding in CPs on corresponding electronic and materials properties. Recent advances in addressing the trade-off between electronic performance and mechanical durability are also highlighted. Furthermore, insights into future directions and prospects for H-bonded CPs are discussed.

Intrinsically Stretchable and Efficient Fully Π-Conjugated Polymer via Internal Plasticization for Flexible Deep-Blue Polymer Light-Emitting Diodes with CIEy = 0.08

Intrinsically stretchable polymeric semiconductors are essential to flexible polymer light-emitting diodes (PLEDs) owing to their excellent strain tolerance capacity under long-time deformation operation. Obtaining intrinsic stretchability, robust emission properties, and excellent charge-transport behavior simultaneously from fully π-conjugated polymers (FCPs) is difficult, particularly for applications in deep-blue PLEDs. Herein, an internal plasticization strategy is proposed to introduce a phenyl-ester plasticizer into polyfluorenes (PF-MC4, PF-MC6, and PF-MC8) for narrowband deep-blue flexible PLEDs. Compared with controlled poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPFs) (2.5%), the freestanding PF-MC8 thin film shows a fracture strain of >25%. The three stretchable films exhibit stable and efficient deep-blue emission (PLQY > 50%) because of the encapsulation of π-conjugated backbone via pendant phenyl-ester plasticizers. The PF-MC8-based PLEDs show deep-blue emission, which corresponds to CIE and EQE values of (0.16, 0.10) and 1.06%, respectively. Finally, the narrowband deep-blue electroluminescence (FWHM of ≈25 nm; CIE coordinates: (0.15, 0.08)) and performance of the transferred PLEDs based on the PF-MC8 stretchable film are independent of the tensile ratio (up to 45%); however, they show a maximum brightness of 1976 cd m-2 at a ratio of 35%. Therefore, internal plasticization is a promising approach for designing intrinsically stretchable FCPs for flexible electronics.