Bandgap tuning of aluminum-doped indium tin oxide for efficient light-emitting diodes

Transparent conductive electrode materials with high transmittance and low resistance are essential cornerstones for realizing high-efficiency optoelectronic devices. Here, we propose a bandgap tuning strategy involving Al doping and thermal annealing to enhance the optical and electrical properties of indium tin oxide (ITO). The ITO thickness, Al doping layer thickness, and the thermal annealing conditions—including annealing temperature, annealing time, and O₂ flow rate—are systematically investigated. The surface morphology of the optimal ITO:Al is significantly improved via optimization of the annealing conditions. The transmittance at 450 nm is increased to 98.4 % and the sheet resistance is reduced to 16.1 Ω/□. X-ray photoelectron spectroscopy analysis reveals that Al atoms substitute for In atoms in the ITO lattice, forming Al–O bonds. By providing a sufficient number of charge carriers and increasing the energy bandgap of ITO, Al doping enhances the conductivity and transmittance of the ITO:Al film. Finally, we employ the optimal ITO:Al as the p-electrode in blue light-emitting diodes, and the improvement in the optoelectronic performance effectively demonstrate the validity of the bandgap tuning strategy. This work provides a systematic study and an effective approach for achieving ITO films with high transmittance and low resistance.