Efficient p-i-n-p blue OLED devices by inserting organic heterojunctions for charge generation

Abstract

An n-p type organic heterojunction composed of various materials was inserted between the Al electrode and the electron injection layer to fabricate an optimized p-i-n-p blue OLED device. The n-p type organic heterojunction generate carriers under reverse bias, reducing the injection barrier for carriers and regulating carrier balance. A p-n junction carrier device was fabricated to investigate their carrier transport properties. The energy levels of the p-layer and n-layer were analyzed using ultraviolet photo-electron spectroscopy (UPS) and low-energy inverse photoelectron spectroscopy (LEIPS). The p-i-n-p OLED with BPhen:15 %Ag₂O (20 nm)/NPB:10 %MoO₃ (10 nm) as the heterojunction shows a remarkable 0.6 V reduction in turn-on voltage. Current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) increase by 29.3 %, 41.2 %, and 12.5 %, respectively, compared to the basic p-i-n OLED. Finally, FTIR spectra indicate a charge generation in the p-n junction, enabling a balanced carrier distribution.