Blue and white organic light-emitting devices using oligo(phenylenvinylene) as a blue emitter

Abstract

Highly bright and efficient blue and white organic light-emitting devices based on oligo(phenylenvinylene) derivatives, 1,4-di(4 -N,Ndiphenylaminostyryl) benzene (DPA-DSB) and 2,5,2 ,5 -tetrastyryl-biphenyl (TSB), are fabricated. In the blue device, using DPA-DSB doped TSB as a blue emitter, due to efficient energy transfer from TSB to DPA-DSB and depression of concentration quenching of the dopant, a maximum brightness of 17 350 cd m −2 and a maximum luminous efficiency of 12.18 cd A −1 are obtained. In the white device, DPA-DSB doped 4,4-N,N -dicarbazolebiphenyl (CBP) acts not only as a blue emitter, but also as a blocking layer to prevent the energy transfer between the two phosphorescent layers in order to balance emissions from the three emissive layers. Combining the blue emission from it with the green and red emissions from the phosphorescent layers, white emission with a maximum brightness of 13 290 cd m −2 and a maximum luminous efficiency of 14.97 cd A −1 is obtained. The colour rendering index of the white device is 79.

Exciplex emission from electroluminescent ladder-type pentaphenylene oligomers bearing both electron- and hole-accepting substituents

“…While the PL efficiencies ͑or quantum yields͒ of these all-in-one materials are found to be in the range of 80%-90% in solution and a few percent in thin films, the EL efficiencies of our basic devices are not found to be in a range comparable with the best reported organic LEDs ͑OLEDs͒. 31,32 Using appropriate calibration parameters to account for the spectral response function of the photodiode detector and the standard eye response function, we typically see surface brightness of order 10-100 cd/ m 2 at relatively high driving voltages of 5 -10 V, current efficiencies of order 0.01-0.1 cd/ A, and external quantum efficiencies of up to 0.1%. A major constraint on the device performance is the very thin nature of the films which may be spin coated from solutions of such oligomeric materials, which have a much lower viscosity than solutions of conjugated polymers, for example.…”

Energy level alignment of electrically doped hole transport layers with transparent and conductive indium tin oxide and polymer anodes

“…10 Another approach for efficient injection of holes into organic layers is the use of polymer layers based on poly͑3,4-ethylenedioxythiophene͒: poly͑styrenesulfonate͒ ͑PEDOT:PSS͒ with an ITO layer underneath. 11,12 Commonly, the ITO layer is needed to provide a homogeneous lateral current distribution due to the several orders of magnitude lower conductivity of the polymer compared to metals or ITO. However, due to the very recent development of highly conductive formulations of PEDOT:PSS with low absorption in the visible, it is now possible to use PEDOT:PSS with a conductivity of up to 500 S / cm as anode without the need of an inorganic layer underneath.…”