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Abstract: We present the results of a systematic study on how the solvent processing affects the EL properties of a single emissive layer white PLED based on a polyfluorene derivative polymer. The EL spectrum of the device using solvent processing, peaked at 436, 572nm, shows a pure white emission and the luminous efficiency is enhanced, which is attributed to the presence of the crystalline polyfluorene induced by solvent processing. The crystalline polyfluorene that acts as the self-dopant enhances the blue emission and increases the purity of the white light. Most importantly, the charge transport is balanced after solvent processing, which favors improving the luminous efficiency. A light-emitting efficiency of 12cd/A is achieved after solvent processing, about 50% increase compared to the as-spincoated device. [Copyright &y& Elsevier]

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]

Abstract: New random poly{benzo[1,2-b:4,5-b'']dithiophene-thieno[3,4-c]pyrrole-4,6-dione-pyrrolo[3,4-c]pyrrole-1,4-dione} (PBDT-TPD-DPP) based on benzo[1,2-b:4,5-b'']dithiophene (BDT) as donor and thieno[3,4-c]pyrrole-4,6-dione (TPD, 60–90%), pyrrolo[3,4-c]pyrrole-1,4-dione (DPP, 10–40%) as acceptors were synthesized through Stille coupling reaction. The photophysical, electrochemical and photovoltaic properties of random polymers were investigated. The random polymers with high molecular weight (M n = 33.5–41.7 kDa) exhibited broad and strong absorption covering the spectra range from 350 nm up to 922 nm with absorption maxima at around 700 nm, the relatively deep highest occupied molecular orbital (HOMO) energy levels vary between −5.25 and −5.42 eV and suitable lowest unoccupied molecular orbital (LUMO) energy levels ranging from −3.85 to −3.91 eV. Polymer solar cells (PSC) based on these new random polymers were fabricated with device structures of ITO/PEDOT: PSS/random polymers: PC71BM (1:2, w/w)/Ca/Al. The photovoltaic properties of random polymers were evaluated under AM 1.5G illumination (100 mW/cm2). Devices based on the random polymers showed open circuit voltage (V oc) of 0.71–0.83 V, and power conversion efficiency (PCE) of 0.82–1.80%. [Copyright &y& Elsevier]

Abstract: Optical loss is a crucial quality for the application of polymer waveguide devices. The optimized oxygen inductively coupled plasma etching conditions, including antenna power, bias power, chamber pressure, O2 flow rate and etching time for the fabrication of smooth vertical poly(methyl-methacrylate-glycidly-methacrylate) channel waveguide were systematically investigated. Atomic force microscopy and scanning electron microscopy were used to characterize the etch rate, surface roughness and vertical profiles. The increment of etch rate with the antenna power, bias power and O2 flow rate was observed. Bias power and chamber pressure were found to be the main factor affecting the interface roughness. The vertical profiles were proved to be closely related to antenna power, bias power and O2 flow rate. Surface roughness increment was observed when the etching time increased. [Copyright &y& Elsevier]

Abstract: Red light-emitting electrophosphorescent polymers with poly(fluorene-alt-carbazole) (PFCz) and poly(3,6-carbazole) (PCz) as the main chain, and the quinoline-based iridium (Ir) complex as the side chain have been synthesized by Suzuki and modified Yamamoto polymerization, respectively. The triplet energy of the polymeric backbone is tuned from 2.1 eV of polyfluorene (PF) to 2.3 eV of PFCz and 2.6 eV of PCz. We find that, with the increasing triplet energy, the lifetime of the triplet excitons gradually increases, but the device efficiency becomes worse. The reason is that the alteration of the main chain structure leads to the increase of the highest occupied molecular orbital (HOMO) level of the polymeric host, which can facilitate the efficient hole injection and transportation. As a consequence of this enhancement of the hole current, charge balance in the emitting layer is destroyed, and correspondingly, the poorer device performance is achieved. Our results, we believe, indicate that besides the triplet energy, charge balance is a crucial determinant to develop high efficiency red light-emitting electrophosphorescent polymers. [Copyright &y& Elsevier]

Abstract: Enhanced performances of hybrid polymer solar cells based on a blend of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and p-methoxybenzoic acid (MBA) modified zinc oxide (ZnO) nanoparticles were reported. Both the short-circuit current and open-circuit voltage of solar cells were improved by using MBA modified ZnO nanoparticles as electron acceptor. The overall power conversion efficiency was increased from 1.09% to 1.52% under AM 1.5G 100mW/cm2 illumination after ZnO was modified with MBA at 0.1wt.%. It was found that modification of ZnO with 0.1wt.% of MBA did not affect electron and hole transport properties of the active layer. However, a fine phase separation between MEH-PPV donor and MBA-modified ZnO acceptor was obtained. The fine phase separation enhanced the exciton dissociation efficiency and hence the power conversion efficiency of solar cells. [Copyright &y& Elsevier]

Abstract: A kind of tandem polymer photovoltaic cell with inorganic metal oxides as a transparent middle connection unit to link the two subcells having different absorption characteristics is developed and its open-circuit voltage origin is investigated. The middle connection unit consists of an electron-transporting titanium oxide (TiO x ) layer, a thin aluminum (Al) layer and a hole-transporting molybdenum oxide (MoO3) layer. The inserted thin Al layer between the TiO x and MoO3 layers not only acts as an efficient recombination site for electrons and holes photo-generated in the two subcells, but also realigns the electronic energy levels at TiO x /MoO3 interfaces to reduce the open-circuit voltage loss. The open-circuit voltage of the tandem cell is the summation of the two subcells. [Copyright &y& Elsevier]

Abstract: Two novel triphenylamine-substituted poly(p-phenylenevinylene) derivatives, P1 and P2, have been successfully synthesized through the Witting–Horner reaction. The structures and properties of the monomers and the resulting polymers were characterized by using 1H NMR, FT-IR, GPC, TGA, UV–vis absorption spectroscopy, cyclic voltammetry (CV) and electroluminescence (EL) spectroscopy. The obtained polymers exhibited good thermal stability and high photoluminescence quantum yield (0.42–0.90). The polymer light-emitting diodes (PLEDs) with the configuration of ITO/PEDOT/polymers/Ca/Al were fabricated. The single-layer device based on P1 and P2 emitted stable blue and yellow light with the turn-on voltage of 4 and 6V, respectively. The maximum luminance of 3003cd/m2 at 10V was obtained for device P2. [Copyright &y& Elsevier]