Researchers at the University of Minnesota have developed a novel organic light-emitting diode (OLED) architecture that reduces the number of individual layers in the device without sacrificing performance. With fewer layers, there are fewer deposition steps, leading to a simpler manufacturing process and a reduction in the overall cost.
The novel architecture combines the hole transport material (HTM), electron transport material (ETM), and light-emitting guest material into a single emissive layer. The composition of HTM and ETM are continuously graded in the mixed emissive region while the concentration of the light-emitting guest material is held constant.
The graded heterojunction architecture integrates the best features of the two competing architectures for OLEDs, which are double emissive layer and uniformly mixed host layer. The double emissive layer has the benefit of good charge injection due to the separate layers but suffers from the long distance between the hole and the electron (thus more interference) while the uniformly mixed host layer has lower interference but poor charge injection. The graded heterojunction architecture preserves the charge injection while reducing interference.
A green OLED was fabricated using existing commercially available materials. The device had an external quantum efficiency of 19.3% and a power efficiency of 67 lm/W. Future expected developments include red and blue OLEDs and lifetime testing.
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