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Efficient multilayer white polymer light-emitting diodes (WPLEDs) with aluminum cathodes are fabricated. The multilayer structure is composed of a water soluble hole-injection layer, a toluene-soluble emissive layer, and an alcohol-soluble emissive layer. The polarity difference of the solvents used for spin coating these polymers allows for realization of the multilayer polymer structure. The recombination zone confined at the interface of the two emissive polymers avoids exciton quenching by electrodes, and white emission is realized by harvesting photons emitted from the two emissive polymers. A maximum luminous efficiency of 16.9 cd/A and a power efficiency of 11.1 lm/W are achieved for this WPLED. [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: 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]