Sungkyunkwan University (SKKU) researchers have developed an indium-free transparent electrode technology for perovskite light-emitting diodes (PeLEDs), achieving high performance, chemical robustness, and improved device stability. The work, led by Professors Han-Ki Kim and Bo Ram Lee, introduces nitrogen-doped tin oxide (NTO) as a cost-effective, sustainable alternative to conventional indium tin oxide (ITO).
Image from: Materials Today
Perovskite LEDs are recognized for their exceptional color purity and processing flexibility, but the reliance on ITO remains a bottleneck due to indium’s rarity, high cost, and poor chemical compatibility with acidic hole transport layers such as PEDOT:PSS. Over time, indium diffusion and electrode corrosion can degrade device performance and shorten operational lifetime.
To overcome these issues, the SKKU team fabricated amorphous NTO thin films using radio-frequency (RF) magnetron sputtering - a scalable, low-cost deposition method compatible with large-area processing. By incorporating a small amount of nitrogen (2.73 at.%), the researchers enhanced the electrical conductivity and chemical stability of SnO₂ through the creation of oxygen vacancies and the formation of strong Sn–N bonds. This unique bonding framework shields the electrode from acid-induced degradation and effectively suppresses metal ion diffusion at the interface.
The optimized NTO electrode delivers a low sheet resistance of 37.37 Ω sq⁻¹, an average visible transmittance of 81.74%, and an ultrasmooth surface with a root-mean-square roughness of 1.2 nm. Its work function of 4.51 eV enables efficient charge injection and balanced carrier transport within the PeLED structure. As a result, PeLEDs incorporating the NTO electrode exhibit a peak external quantum efficiency (EQE) of 20.82% at 514 nm emission and a maximum luminance of 5323.8 cd m⁻², while demonstrating more than twice the operational lifetime compared to ITO-based devices.
According to Professor Han-Ki Kim, “This work fundamentally addresses the limitations of conventional transparent electrode technologies that rely on expensive rare metals. It represents a major step toward sustainable, high-performance optoelectronic devices.” He added that this approach could accelerate the adoption of indium-free electrodes across emerging display and photovoltaic applications.
