In this work, we study the electrical and optical properties of organic light-emitting diodes (OLEDs) with a lithium (Li)-doped tris(8-hydroxyquinolino)-aluminum (Alq 3 ) electron transport layer (ETL). When the Li : Alq 3 doping ratio in a Li-doped Alq 3 ETL is 2 : 1, the luminous efficiency of OLEDs is 5.25 cd/A; that of an OLED without a Li-doped Alq 3 ETL is only 0.7 cd/A. X-ray photoelectron (XPS) and UV-vis absorption spectra of Li-doped Alq 3 films reveal that the Li-doped Alq 3 ETL has an improved electron conductivity. However, heavy Li doping in a Li-doped Alq 3 ETL reduces the optoelectric performance of OLEDs. Excess Li atoms or cations quench light-emitting excitons in an Alq 3 emitting layer (EML). Additionally, annealing improves the morphological stability of Li-doped Alq 3 films. An OLED, comprising a Li-doped Alq 3 ETL, requires no extrinsic thin LiF film, meeting commercial requirements, improving reproducibility and ensuring uniformality in a large area.

In this study, indium-tin-oxide (ITO) films were used as p-contacts in GaN-based light-emitting diodes (LEDs). The dependence of the optoelectronic performance of LEDs on various annealing temperatures of ITO films was studied. At an annealing temperature of 600°C the transmittance of ITO films can reach 98.6% at a wavelength of 470nm . The specific contact resistance characterized by the circular transmission line model is as low as 7.73×10−3Ωcm2 . Furthermore, GaN-based LEDs employing an ITO p-contact annealed at 600°C have high luminescence intensities of 243.2 mcd at a 20mA injection current. Under the same injection current, the proposed LED also has the largest electroluminescence intensity with the ITO p-contact annealed at 600°C .

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