Improvement of OLED performances by applying annealing and surface treatment on electro-deposited CuSCN hole injection layer

In this study, we demonstrated an organic light-emitting diode (OLED) using electro-deposited CuSCN as a hole-injection layer. The effects of thermal annealing and UV-Ozone treatments on ITO/CuSCN/organic interfaces were investigated. By employing both UV-O₃ and proper thermal annealing (75 ° C, 20 min), Cu₂O was found on the surface of CuSCN. With these treatments, the surface roughness of the organic deposited on CuSCN was reduced from 4.25 to 1.28 nm. The optical transmittance was also enhanced. Additionally, the CuSCN surface energy and polarity were considerably increased and the hole-injection barrier was decreased from 0.70 to 0.47 eV. The interface dipole effects lead to better adhesion between CuSCN/organic interface and facilitate the hole injection capability from anode ITO due to the formation of superficial Cu₂O. The underlying mechanisms were illustrated by surface energy, X-Ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) measurements. As a result, these significantly enhanced CuSCN characteristics led to improved OLED performances, which achieved a hundred-fold efficiency compared to the device without any treatment. With this realization of integrating electro-deposited CuSCN into conventional organic optoelectronic systems, it could bring various practical benefits particularly concerning industrial interests in low-temperature, cost-effective, and large-area fabrication techniques.