Organic light-emitting diodes with an electro-deposited copper(I) thiocyanate (CuSCN) hole-injection layer based on aqueous electrolyte

Copper(I) thiocyanate (CuSCN) has been drawing much attention in optoelectronics due to its exceptional optical and electrical properties, as well as its processing versatility. The first organic light-emitting diodes (OLEDs) integrated with electro-deposited CuSCN crystalline thin films based on aqueous electrolyte were fabricated. With precisely tuned deposition parameters, the CuSCN thin films with satisfactory surface roughness and sufficient grain density were realized. We found that the driving voltage (voltage at a current density of 100 mA/cm²) and turn-on voltage of OLEDs using CuSCN as the hole injection layer (HIL) can be reduced by 1.41 and 1.79 V, respectively, compared with devices using vacuum-deposited hole injecting transition metal oxide molybdenum trioxide (MoO₃). Moreover, the fabricated OLEDs also demonstrated considerably mitigated efficiency roll-off. Optical and energetic analyses were conducted to investigate the characteristics and enhancement mechanisms. Efficient hole-injection, electron blocking, improved charge balance, enhanced optical properties and good compatibility of electro-deposited CuSCN with thermally evaporated organic systems were found to be the primary contributors for the performance improvements of the OLEDs.