The application of a non-doped composite hole transport layer of [MoO/CBP] with multi-periodic structure for high power efficiency organic light-emitting diodes.

A non-doped multi-periodic structure of composite hole transport layer of [MoO/CBP] was applied to organic light-emitting diodes. All devices with such hole transport layers showed low turn-on voltage of about 3 V, ultra-high luminance of >110 000 cd m, high current efficiency of >50 cd A, and high EQE of more than 15%. The optimized device exhibited power efficiency increase of 66% and 18% relative to the single periodic and doped structure OLEDs. The achievement of the reduced driving voltage and improved power efficiency can be attributed to the significantly enhanced hole injection and transport induced by the multi-periodic structure of composite hole transport layer, which was demonstrated a series of hole-only devices. For improved hole injection and transport mechanism, we also provided a detailed discussion in combination with atomic force microscopy measurements.