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over fullerene-based PSCs, including easily tunable polymer properties, simultaneous light absorption by both donors and acceptors, and enhanced stability against mechanical and thermal stresses. [1] However, few all-PSCs have been reported to exhibit power conversion efficiencies (PCEs) higher than 7%, as many systems have relatively low short-circuit current densities (J SC ) and fill factors (FF). [1d,e,2] The low performance of all-PSCs is mainly attributed to (i) low electron mobility of polymer acceptors within the photoactive layer and (ii) inefficient exciton dissociation at donor/acceptor (D/A) interfaces as a result of the anisotropic packing structure of donor and acceptor polymers. [3] Another hurdle for efficient exciton dissociation is lower dielectric constant of the polymers than that of fullerene derivatives, which increases the binding energy of the excitons in all-PSCs. [4] To develop polymer acceptors with high electron mobility, various n-type polymers have been designed and synthesized, among which naphthalenediimide (NDI)-based copolymers have attracted great attention due to strong π-π interactions between NDI units and facile functionalization through the N-position of NDI moiety. [1b,c,2a,c,5] However, lowest unoccupied molecular orbital (LUMO) of NDI-based polymers is often largely localized on the NDI units due to the high electron affinity of NDI, which hinders efficient intermolecular electron transport. [5n,6] Thus, insertion of strong electron-withdrawing groups into the electron donating moieties of the NDI-based copolymers would be a promising approach to enhance electron transport and intermolecular interactions by delocalizing the LUMO over the polymer backbone and generating stronger orbital overlaps between the adjacent polymer chains. [6a,b] Charge generation at the interfaces of the D/A polymer domains within the photoactive layer depends significantly on the interfacial dipole moment between the donor and acceptor and the internal dipole moment of the polymers. [3a,5l,7] Additionally, for conjugated polymers with a large dipole moment difference between the ground and excited states (Δµ ge ), the electron-hole separation distance within the polymer chain increases as the polarized exciton is formed, which reduces the Designing polymers that facilitate exciton dissociation and charge transport is critical for the production of highly efficient all-polymer solar cells (all-PSCs). Here, the development of a new class of high-performance naphthalenediimide (NDI)-based polymers with large dipole moment change (Δµ ge ) and delocalized lowest unoccupied molecular orbital (LUMO) as electron acceptors for all-PSCs is reported. A series of NDI-based copolymers incorporating electron-withdrawing cyanovinylene groups into the backbone (PNDITCVT-R) is designed and synthesized with 2-hexyldecyl (R = HD) and2-octyldodecyl (R = OD) side chains. Density functional theory calculations reveal an enhancement in Δµ ge and delocalization of the LUMO upon the incorporation of cyano...

Recently, bipolar host materials are the most promising candidates for achieving high performance phosphorescent organic light-emitting diodes (PHOLEDs) in order to maximize recombination efficiency. However, the development of host material with high triplet energy (E T ) is still a great challenge to date to overcome the limitations associated with the present PHOLEDs. Herein, a highly efficient donor-π-acceptor (D-π-A) type bipolar host (4′-(9H-carbazol-9-yl)-2,2′-dimethyl-[1,1′-biphenyl]-4-yl)diphenylphosphine oxide (m-CBPPO) comprising of carbazole, 2,2′-dimethylbiphenyl and diphenylphosphoryl as D-π-A unit, respectively, is developed. Interestingly, a high E T of 3.02 eV is observed for m-CBPPO due to highly twisted conformation. Furthermore, the new host material is incorporated in PHOLEDs as emissive layer with a new carbene type Ir(cb) 3 material as a deep-blue emitter. The optimized devices show an excellent external quantum efficiency (EQE) of 24.8%with a notable Commission internationale de l'éclairage (x, y) ≤ 0.15, (0.136, 0.138) and high electroluminescence performance with extremely low efficiency roll-off. Overall, the above EQE is the highest reported for deep-blue PHOLEDs with very low efficiency roll-off and also indicate the importance of appropriate host for the development of high performance deep-blue PHOLEDs.

The performance of all-polymer solar cells (all-PSCs) is often limited by the poor exciton dissociation process. Here, the design of a series of polymer donors (P1-P3) with different numbers of fluorine atoms on their backbone is presented and the influence of fluorination on charge generation in all-PSCs is investigated. Sequential fluorination of the polymer backbones increases the dipole moment difference between the ground and excited states (Δµ ge ) from P1 (18.40 D) to P2 (25.11 D) and to P3 (28.47 D). The large Δµ ge of P3 leads to efficient exciton dissociation with greatly suppressed charge recombination in P3-based all-PSCs. Additionally, the fluorination lowers the highest occupied molecular orbital energy level of P3 and P2, leading to higher opencircuit voltage (V OC ). The power conversion efficiency of the P3-based all-PSCs (6.42%) outperforms those of the P2 and P1 (5.00% and 2.65%)-based devices. The reduced charge recombination and the enhanced polymer exciton lifetime in P3-based all-PSCs are confirmed by the measurements of light-intensity dependent short-circuit current density (J SC ) and V OC , and time-resolved photoluminescence. The results provide reciprocal understanding of the charge generation process associated with Δµ ge in all-PSCs and suggest an effective strategy for designing π-conjugated polymers for high performance all-PSCs.

Deep‐blue triplet emitters remain far inferior to standard red and green triplet emitters in terms of exhibiting high‐color‐purity Commission International de l'Éclairage (CIE) y values of ≤0.1, external quantum efficiencies (EQEs), and high electroluminescent brightnesses in phosphorescent organic light‐emitting diodes. In fact, no deep‐blue triplet emitter with color purity and high device performance has previously been reported. In this study, a deep‐blue triplet emitter, mer‐tris(N‐phenyl, N‐benzyl‐pyridoimidazol‐2‐yl)iridium(III) (mer‐Ir1) is developed, which meets the requirements of the National Television System Committee (NTSC) CIE(x, y) coordinates of (0.149, 0.085) with an extremely high EQE of 24.8% and maximum brightness (Lmax) of 6453 cd m−2, by a device with a 40 vol% doping ratio. Moreover, another device demonstrates an EQEmax of 21.3%, an Lmax of 5247 cd m−2, and CIE(x, y) coordinates of (0.151, 0.086) at a 30 vol% doping ratio. This is the first report of a high‐performance, deep‐blue phosphor, carbene‐based Ir(III) complex device with outstanding CIE(x, y) color coordinates and a high EQE. The results of this study indicate that the novel dopant mer‐Ir1 is a promising candidate for reducing power consumption in display applications.

Three new highly efficient green-emitting heteroleptic phosphorescent iridium(III) complexes are designed and synthesized for the fabrication of solution-processable phosphorescent organic light-emitting diodes (PHOLEDs). Their photophysical, thermal, and electroluminescent (EL) properties are systematically investigated. The Ir(III) complexes comprise an amide-bridged trifluoromethyl (CF 3 )-substituted phenylpyridine unit as the main ligand and picolinic acid (pic) and tetraphenylimidodiphosphinate (tpip) as ancillary ligands. In addition, the 2-ethoxyethnol (EO 2 ) solubilizing group is attached to the 4-position of pic ancillary ligand via tandem reaction, which improved the absolute photoluminescence quantum yields (PLQYs) and EL performance. The high-performance solution-processable PHOLEDs based on the bis[5-methyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one](4-(2-ethoxyethoxy picolinate) iridium(III) (Ir1) complex exhibit a maximum external quantum efficiency (EQE) of 24.22% and a maximum current efficiency (CE) of 92.44 cd A −1 , with the latter being among the best reported CEs achieved though solution processing. In contrast, PHOLEDs with the bis[5-hexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one] (tetraphenylimidodiphosphinato)iridium (Ir3) complex show extremely low efficiency roll-off, with an EQE max of 19.40% and an EQE of 19.29% at 10 000 cd m −2 .

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