Incorporation of Designed Donor–Acceptor–Donor Segments in a Host Polymer for Strong Near-Infrared Emission from a Large-Area Light-Emitting Electrochemical Cell

Abstract

Cost-efficient thin-film devices that emit in the nearinfrared (NIR) range promise a wide range of important applications. Here, the synthesis and NIR application of a series of copolymers comprising poly [indacenodithieno[3,2-b]thiophene-2,8-diyl] (PIDTT) as the host and different donor−acceptor−donor (DAD) segments as the guest are reported. We find that a key design criterion for efficient solid-state host-to-guest energy transfer is that the DAD conformation is compatible with the conformation of the host. Such host−guest copolymers are evaluated as the emitter in light-emitting electrochemical cells (LECs) and organic light-emitting diodes, and the best performance is invariably attained from the LEC devices because of the observed balanced electrochemical doping that alleviates issues with a noncentered emission zone. An LEC device comprising a host−guest copolymer with 4,4bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene as the donor and benzo[c][1,2,5]thiadiazole as the acceptor delivers an impressive near-infrared (NIR) performance in the form of a high radiance of 1458 μW/cm 2 at a peak wavelength of 725 nm when driven by a current density of 500 mA/cm 2 , a second-fast turn-on, and a good stress stability as manifested in a constant radiance output during 3 days of uninterrupted operation. The high-molecular-weight copolymer features excellent processability, and the potential for low-cost and scalable NIR applications is verified through a spray-coating fabrication of a >40 cm 2 large-area device, which emits intense and uniform NIR light at a low drive voltage of 4.5 V.

Combining Benzotriazole and Benzodithiophene Host Units in Host–Guest Polymers for Efficient and Stable Near‐Infrared Emission from Light‐Emitting Electrochemical Cells

“…Table and the inset in Figure c reveal that the turn‐on time to significant light emission is very fast in the few‐seconds range, particularly for the PBDTTBTzT* LEC but also for the PBDTBTz* LEC. This implies that the ion transport is facile in these two active materials, presumably because of a good compatibility between the polymeric emitter and the electrolyte . We further suggest that the slower turn‐on kinetics for the PBDTTBTzFT* LEC could be due to hydrogen bonding within the conjugated‐copolymer phase, which slows down the ion motion by limiting the free volume.…”

“…Materials and Synthesis : The synthesis of the dibromo‐substituted TBT monomer and the dibromo‐substituted BTz, TBTzT, TBTzFT monomers followed procedures in the literature. The distannyl‐substituted BDT monomer was purchased from Solarmer Energy Inc., while the other materials and solvents were obtained from Merck.…”

“…Albeit promising, these studies suffer from that a high‐frequency operation depends on a converter circuit in mobile applications, that Ru is a rare and expensive compound, and that the measured lifetime of the Ru‐based NIR‐LEC was very limited at a mere 20 min. Our group recently reported on NIR‐LECs based on an emissive host–guest copolymer with indacenodithieno[3,2‐ b ]thiophene (IDTT) as the single host unit, which delivered NIR emission centered at 725 nm with a high radiance of 263 µW cm −2 when driven by a constant current …”

Retracted Article: Facile preparation of bithiazole-based material for inkjet printed light-emitting electrochemical cell

“…[14][15][16] The most efficient device used to date for LECs are biscyclometalated iridium(III) (Ir) complexes, because they have highly efficient and stable devices spanning the whole visible range. [17][18][19] However, avoiding the use of Ir is strongly desired because of its high cost and limited supply. [20][21][22] Till now, thiazole has worked as active component in a LECs system with a long-lived charge-separation molecule, without additional ions in its active layer.…”

Structural engineering of pyrrolo[3,4-f]benzotriazole-5,7(2H,6H)-dione-based polymers for non-fullerene organic solar cells with an efficiency over 12%

“…The donor-acceptor (D-A) alternating conjugated polymer synthesis is the commonly used strategy to prepare efficient donor polymers. In this regard, among the commonly investigated wide band-gap polymers are thieno [3,4-c]pyrrole-4,6-dione [17][18][19] (TPD)-, [2,1,3]benzothiadiazole [20][21][22][23][24][25][26][27] (BT)-and 2H-benzo [d] [1,2,3]triazole 8,[28][29][30][31] (BTz)-based D-A conjugated polymers. Yin et al 32 combined TPD and BT to garner the advantages of solubility and deep HOMO energy levels simultaneously, and synthesized the [2,1,3]benzothiadiazole-5,6dicarboxylic imide-based acceptor monomer 4,8-bis(5-bromothiophen-2-yl)-6-(2-ethylhexyl)-5H- [1,2,5]thiadiazolo [3,4-f]isoindole-5,7(6H)-dione.…”