A SnO₂/ZnO Nanoparticle Bilayer Electron Transport Layer for Regulated Electron Injection in Quantum-Dot...

ZnO is widely used as an electron transport layer in quantum-dot light-emitting diodes (QLEDs) because of its high electron mobility and suitable energy levels. However, rapid electron transport may cause excessive electron injection, leading to charge accumulation and parasitic recombination. SnO₂ provides weaker electron transport, but using it alone limits device performance. Here, a SnO₂/ZnO bilayer electron transport layer was introduced to regulate electron injection. Unlike previously reported structures in which SnO₂ directly contacts the QDs, the present configuration places SnO₂ on ITO and ZnO adjacent to the QD layer. The low-concentration ZnO overlayer reduced the RMS roughness of the SnO₂ film from 1.79 to 1.07 nm and facilitated electron injection, while the underlying SnO₂ layer moderated the electron supply. The bilayer also suppressed leakage current and showed the lowest capacitance peak, consistent with improved charge balance. The bilayer QLED achieved a maximum current efficiency of 13.40 cd/A and a maximum luminance of 33,210 cd/m². Its current efficiency was 100% and 32.7% higher than those of the SnO₂ and ZnO devices, respectively. These results demonstrate that the bilayer improves charge balance through facilitated electron injection and controlled electron supply.