Oxygen vacancy-induced red light emission from flexible inorganic micropatterned p-CuO/n-ZnO heterojunction light-emitting diode

Fully inorganic flexible light-emitting diodes (LEDs) were demonstrated by using CuO nanorods (NRs) and ZnO NRs as the hole and electron transport materials, respectively. The heterojunctions were fabricated inside 5 μm square patterns in order to achieve better flexibility. The current-voltage characteristic of the heterojunction revealed a typical p-n diode nature with an on-off ratio of 8.6 × 10² at 4 V, a turn-on voltage of 2.8 V, and a stable current flow at different voltage stress. The electroluminescence spectra from the LED at different forward bias exhibited eminent peak at around 710 nm corresponding to red light, which was in accordance with the deep-level emission of photoluminescence spectra of ZnO NRs. The Zn 2p and O 1s narrow-scan X-ray photoelectron spectra revealed that the deep levels are related to oxygen vacancies. The devices showed significant stability during bending test and continued to emit light beyond 1000 cycles of dynamic bending at a radius of curvature of 5 mm.