Double-layer structured hole injection layer to enhance quantum-dot light-emitting diodes

Highlights: • A double-layer structured hole injection layer was formed using two different PEDOT:PSS. • Quantum-dots light emitting diodes was fabricated using a double layer hole injection layer. • Double-layer structured hole injection layer improved the hole injection characteristics. • The origin of the improvement was analyzed using photoelectron spectroscopy. • Density of states of PEDOT:PSS was increased with highly conductive PEDOT:PSS. -- Abstract: Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a commonly used hole injection layer (HIL) in quantum-dot light-emitting diodes (QLEDs). In this study, we investigated a double-layer structured HIL based on PEDOT:PSS to improve the hole injection for high-performance QLEDs. Two different types of PEDOT:PSS, having different conductivities, were used to form a double-layer structured HIL, and we observed improved hole injection behavior of the device. The origin of the enhanced hole injection was investigated using ultraviolet and X-ray photoelectron spectroscopy. We found that the density of state for the hole injection and transport was increased at the HIL when we formed a double-layer structured HIL for the device, compared to the QLEDs with a single layer PEDOT:PSS HIL. Therefore, high-performance QLEDs were fabricated using a double-layer structured HIL, and the maximum luminance and luminous efficiency of the devices were measured as 53,109 Cd/m² and 2.1 Cd/A, respectively. Our results suggest that a double-layer structured HIL based on PEDOT:PSS is a suitable HIL to improve QLEDs.