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We have designed and synthesized two wide bandgap new donor‐acceptor (D‐A) copolymers consisting of the same alkylthiazole‐substituted benzo[1,2‐b;4,5‐b′]dithiophene (BDTTz) donor unit and but different acceptor units, i.e., thiazolo[5,4‐d]thiazole (TTZ) (P122) and 1,3,‐4 thiadiazole (TDz) (P123) and investigated their optical and electrochemical properties. We have employed these copolymers as donor and fullerene (PC71BM) and narrow bandgap non‐fullerene (Y6) as acceptor, to fabricate binary and ternary bulk heterojunction polymer solar cells (PSCs). The overall power conversion efficiency (PCE) of optimized binary bulk heterojunction PSCs based on P122:Y6 and P123:Y6 is 12.60% and 13.16%, respectively. The higher PCE for PSCs based on P123 than P122 counterparts may be associated with the broader absorption profile of the P123 and more charge carrier mobilities than that for the P122 active layer. With the incorporation of small amount of PC71BM into either P122:Y6 or P123:Y6 binary blend, the corresponding ternary PSCs showed an overall PCE of 14.89% and 15.52%, respectively, which is higher than the binary counterparts using either Y6 or PC71BM as acceptor. Incorporating the PC71BM in the binary host blend increases the absorption in the 300–500 nm wavelength region, generating more excitons in the active ternary layer and helping to dissociate the excitons into free charge carriers more effectively. The more appropriate nanoscale phase separation in the active ternary layer than the binary counterpart may be one of the reasons for higher PCE. [ABSTRACT FROM AUTHOR]

Two D‐A copolymers consisting of fused ring pyrrolo‐dithieno‐quinoxaline acceptors are synthesized with different donor units, i.e., benzodithiophene (BDT) with alkylthienyl (P134) and 2‐ethylhexyloxy (P117) side chains. These copolymers are used as donors and a narrow bandgap acceptor Y6 to fabricate bulk heterojunction polymer solar cell devices. Owing to the strong electron‐deficient fused ring pyrrolo‐bithieno‐quinoxaline and weak alkyl thienyl side chains in BDT, the polymer solar cells (PSCs) based on P134:Y6 attain the power conversion efficiency (PCE) of 15.42%, which is higher than the P117:Y6 counterpart (12.14%). The superior value of PCE for P134:Y6 can be associated with more well‐adjusted charge transport, weak charge recombination, proficient exciton generation, and dissociation into free charge carriers and their subsequent charge collection owing to the dense π–π stacking distance and more considerable crystal coherence length for the P134:Y6 thin films. This investigation confirms the great potential of a strong acceptor‐weak donor tactic for developing efficient D‐A copolymers consists of quinoxaline acceptor for PSCs. [ABSTRACT FROM AUTHOR]

A new acceptor unit anthra[1,2‐b: 4,3‐b': 6,7‐c'']trithiophene‐8,12‐dione (А3Т) (A2) is synthesized and used to design D‐A1‐D‐A2 medium bandgap donor copolymers with same thiophene (D) and A2 units but different A1, i.e., fluorinated benzothiadiazole (F‐BTz) and benzothiadiazole (BTz) denoted as P130 and P131, respectively. Their detailed optical and electrochemical properties are examined. The copolymers show good solubility in common organic solvents, broad absorption in the visible spectral region from 300 to 700 nm, and deeper HOMO levels of −5.45 and −5.34 eV for P130 and P131, respectively. Finally, an optimized polymer solar cell (PSC) based on P131 as the donor and narrow bandgap non‐fullerene small molecule acceptor Y6 demonstrated a power conversion efficiency (PCE) of >11.13%. To further improve the efficiency of the non‐fullerene PSC, the P130 is optimized by introducing a fluorine atom into the BTz unit, F‐BTz acceptor unit, and PCE PSC based on P130: Y6 active layer increased to >15.28%, which is higher than that for the non‐fluorinated analog P131:Y6. The increase in the PCE for former PSC is attributed to the more crystalline nature and compact π–π stacking distance, leading to more balanced charge transport and reduced charge recombination. These remarkable results demonstrate that A3T‐based copolymer P130 with F‐BTz as the second acceptor is a promising donor material for high‐performance PSCs. [ABSTRACT FROM AUTHOR]

A feasible strategy, backbone‐acceptor and pendant‐donor, for constructing thermally activated delayed fluorescence (TADF) conjugated polymer is presented. In the obtained polymers PSAQFx, the backbone consists of dibenzothiophene‐S,S‐dioxide (S) and 6,7‐difluoroquinoxaline (QF), while two 9,10‐dihydroacridine (A) groups as pendants are grafted on QF acceptor through phenylene bridges. Compared to the model compound AQF, the polymers exhibit redshifted emission owing to extended conjugation along the acceptor backbone. Photoluminescence quantum yields can be improved by managing the molar content (x) of the AQF unit and reach the maximum of 91% for PSAQF5 in neat film. Solution‐processed organic light‐emitting diodes (OLEDs) using these polymers as the emitters achieve a maximum external quantum efficiency (EQE) of 24.8% and a maximum power efficiency of 68.5 lm W−1 with the emission peak at 608 nm and luminance at 58 cd m−2. This is the first example of achieving EQE above 20% with emission peak over 600 nm in the polymer TADF OLEDs. [ABSTRACT FROM AUTHOR]

Polymerization could be a feasible method to overcome the rigid structure induced self‐quenching effect in conventional thermally activated delayed fluorescence (TADF) emitters. Despite steady progress in TADF polymer research, developing an efficient red TADF polymer still remains a great challenge because of the large non‐radiative internal conversion rate governed by the energy gap law. Herein, a novel strategy for constructing a red TADF conjugated polymer is presented by means of embedding quinoxaline‐6,7‐dicarbonitrile (QC) as an acceptor into a polycarbazole (PCz) backbone and attaching donor 9,10‐dihydroacridine (A) as a pendant. The obtained polymers PCzAQCx with the appropriate molar content of the AQC unit (x ≥ 0.5) exhibit efficient TADF features with a dominant emissive peak at 627−661 nm and a photoluminescence quantum yield of up to 76% in neat film. The non‐doped electroluminescent devices with the polymers produce red emissions with a maximum external quantum efficiency (EQE) of up to 12.5% and the emission peak at 620 nm, which represents state‐of‐the‐art performance for solution‐processed devices based on red TADF polymers. Furthermore, combined with a blue TADF emitter, the bright white devices with tunable spectra cover the whole visible–near infrared range from 400 to 900 nm and a record‐high EQE of up to 22.4% is achievable. [ABSTRACT FROM AUTHOR]

A series of novel donor–acceptor (D–A) random conjugated terpolymers P2‐P4 along with the homopolymers P1 (BDT‐DPP) and P5 (BDT‐BTDQ) were designed and synthesized by copolymerizing a benzo[1,2‐b:4,5‐b]dithiophene (BDT) donor with an electron‐deficient diketopyrrolo[3,4‐c]pyrrole (DPP) unit and a benzothiadiazolo[3,4‐e]quinoxaline (BTDQ) moieties of different electron‐withdrawing strengths, and the resultant terpolymers showed broad absorption profile ranging from 300 to 1200 nm. The HOMO levels of the polymers were adjusted from −5.23 to −5.11 eV, and the optical bandgaps were controlled from 1.32 to 1.13 eV by changing the molar ratio of DPP and BTDQ acceptors. These terpolymers were used as a donor along with PC71BM as an acceptor for the creation of polymer solar cells, and the performance was optimized via variable the donor to acceptor ratio and solvent vapor annealing. The polymer solar cells made from the random terpolymer P3 showed the highest overall power conversion efficiency of (9.27%), which is higher than that for the corresponding homo‐polymers counterparts, that is, P1 (7.27%) and P5 (7.68%). The results demonstrate that the designing of random D‐A1‐D‐A2 terpolymers may be the best approach for efficient polymer solar cells. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1478–1485 [ABSTRACT FROM AUTHOR]

A cross-linkable conjugated polymer with bromo groups on the side chain has been developed and used as an anode interlayer to improve the active layer morphology and consequently enhance the device performance of polymer solar cells (PSCs). The polymer, PCDTBT-Br, has cross-linkable bromo groups attached to the side chain of a widely-used donor polymer, poly[N-9-heptadecanyl-2,7-carbazole- alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT). The pendant bromo groups do not significantly change the LUMO/HOMO energy levels and absorption spectrum of the PCDTBT polymer backbone. PDCTBT-Br can crosslink under UV irradiation to give a robust film, which enables multilayer PSC device fabrication. Moreover, the much lower surface energy of PCDTBT-Br (20.4 mJ m−2) compared to PEDOT:PSS (91.6 mJ m−2) is beneficial for achieving optimal active layer morphology. As a result, with PCDTBT:[6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) as the active layer, the PSC device with PCDTBT-Br as the underlying layer shows a power conversion efficiency (PCE) of 6.59 %, in comparison to a PCE of 5.86 % of the control device. The device performance enhancement is ascribed to the much improved phase separation with a fibrillar nanostructure in the active layer. [ABSTRACT FROM AUTHOR]

We demonstrate that polymer electron acceptors with excellent all-polymer solar-cell (all-PSC) device performance can be developed from polymer electron donors by using B←N units. By alleviating the steric hindrance effect of the bulky pendant moieties on the conjugated polymers that contain B←N units, the π-π stacking distance of polymer backbones is decreased and the electron mobility is consequently enhanced by nearly two orders of magnitude. As a result, the power conversion efficiency of all-PSCs with the polymer acting as the electron acceptor is greatly improved from 0.12 % to 5.04 %. This PCE value is comparable to that of the best all-PSCs with state-of-the-art polymer acceptors. [ABSTRACT FROM AUTHOR]

A double B←N bridged bipyridyl (BNBP) is a novel electron-deficient building block for polymer electron acceptors in all-polymer solar cells. The B←N bridging units endow BNBP with fixed planar configuration and low-lying LUMO/HOMO energy levels. As a result, the polymer based on BNBP units (P-BNBP-T) exhibits high electron mobility, low-lying LUMO/HOMO energy levels, and strong absorbance in the visible region, which is desirable for polymer electron acceptors. Preliminary all-polymer solar cell (all-PSC) devices with P-BNBP-T as the electron acceptor and PTB7 as the electron donor exhibit a power conversion efficiency (PCE) of 3.38 %, which is among the highest values of all-PSCs with PTB7 as the electron donor. [ABSTRACT FROM AUTHOR]

The key parameters of conjugated polymers are lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Few approaches can simultaneously lower LUMO and HOMO energy levels of conjugated polymers to a large extent (>0.5 eV). Disclosed herein is a novel strategy to decrease both LUMO and HOMO energy levels of conjugated polymers by about 0.6 eV through replacement of a CC unit by a B←N unit. The replacement makes the resulting polymer transform from an electron donor into an electron acceptor, and is proven by fluorescence quenching experiments and the photovoltaic response. This work not only provides an effective approach to tune the LUMO/HOMO energy levels of conjugated polymers, but also uses organic boron chemistry as a new toolbox to develop conjugated polymers with high electron affinity for polymer optoelectronic devices. [ABSTRACT FROM AUTHOR]

Solution-processed white organic light-emitting diodes (WOLEDs) have drawn great attention both in the academic and industrial research communities due to the potential application in low-cost, large-area, solid-state lightings. Issues related to the device efficiencies are largely hampering progress in this field. Alongside the development of new materials and novel device architectures, distinct progress has been made for such white devices. In particular, the all-phosphorescent light-emitting strategy has been intensively developed in recent years, mainly focusing on a hostguest, doping-system-based, single-active-layer structure and a solution-processed, multilayer device structure. Novel approaches, including white single polymers and excimer-/exciplex-based white devices, have also appeared as a promising choice and received great attention. As a prerequisite, the issue of the morphology of the emissive layer is also important and has an influence on the optoelectronic behavior of the device. Herein, major advances in solution-processed WOLEDs based on polymers, dendrimers, or solution-processed small molecules are summarized. Special attention is focused on the main progress in high-efficiency, solution-processed WOLEDs with the key strategies mentioned above and the morphology issue in these systems. The remaining challenges in pursuing the development of reliable and energy-saving lighting devices are also discussed. [ABSTRACT FROM AUTHOR]

The back cover page of the journal "Angewandte Chemie International Edition" is presented.

It is reported a kind of solution-processible transparent conductive film consisting of reduced graphene oxide (rGO) nanosheets and silver nanowires (AgNWs). The sandwiched structure of rGO/AgNWs/rGO is readily deposited via layer-by-layer blade-coating on the rigid glass or flexible PET substrate at mild annealing temperature. The rGO nanosheets sandwiching the AgNWs networks not only induce close contact of the AgNWs networks as a clipper to improve the conductivity, but also link the discrete AgNWs as a connector to improve the uniformity of the film conductivity. The transparent rGO/AgNWs/rGO film exhibits sheet resistance as low as 14.29 Ω/□ with transmittance over 90% at 550 nm. Moreover, the rGO/AgNWs/rGO composite film shows good ambient stability due to the rGO coverage and the existing charge interaction between AgNWs and rGO. Polymer solar cells are fabricated on the transparent rGO/AgNWs/rGO-coated glass or flexible PET substrates and they exhibit comparable photovoltaic perfromance to the control devices fabricated on the commercial ITO substrate. More importantly, the PSCs based on the rGO/AgNWs/rGO/PET substrate show more excellent flexibility than that of the device based on the ITO/PET substrate. [ABSTRACT FROM AUTHOR]

• Effect of the polymer M n on the TADF property was explored for the first time. • More compacted stacking and better energy transfer is observed in low M n polymers. • Low M n polymer achieves a record-high maximum EQE of 21.2 % at 628 nm. Thermally activated delayed fluorescence (TADF) polymers have made remarkable progress in solution processed organic light-emitting diodes (OLEDs) due to their superior film-forming stability. However, the effect of some factors such as the molecular weight and end groups on the optoelectronic properties is never explored so far. Herein, a set of the TADF conjugated polymers with the different number-average molecular weights (M n s) of 5.4, 24.8, 41.8 and 146.1 kg/mol are synthesized and their M n effect on the photoluminescence (PL) and electroluminescence (EL) is systematically investigated. The microstructure models of the spin-coated polymer films based on the M n and chain length are proposed for realizing efficient non-doped OLEDs. Low M n produces more compacted polymer chain stacking and smoother film morphology, leading to restricted non-radiative loss and more effective energy transfer. In particular, the polymers with low M n s of 5.4 and 24.8 kg/mol achieve the higher PL quantum yields and more efficient reverse intersystem cross from triplet to singlet excited state, as well as the record external quantum efficiencies of 21.2 % and 18.4 % with the EL emission peaks over 620 nm. In contrast, the PL and EL performances eventually deteriorate with further increasing M n s due to the sparser chain stacking and larger phase separation. The results show that the lower M n s enable the rigid polymers to form perfect amorphous films and render the luminescent unit more uniform distribution, similar to the classical doped systems, improving the EL behaviors of the polymers. [ABSTRACT FROM AUTHOR]