Composite materials have attracted significant attention owing to their effective application in producing high-efficiency organic light emitting diodes (OLEDs). Hole transport layers are important and play a noteworthy character in improving the efficiency and stability of OLED. In this work, we have investigated the doping effect of the copper iodide (CuI) into copper (II) phthalocyanine (CuPC) hole transport layer on the performance of OLED. The composite hole transport layer was employed in solution processed OLED consisting 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP) as a host, Tris (2-phenylpyridine) iridium (III) (Ir(ppy)3) as dopant, 2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) as electron transport layer, lithium fluoride as electron injection layer, and aluminum as cathode. We perceived that doping of CuI into CuPC led to a higher performance enhancement for the OLED than the use of PEDOT:PSS as hole transport layer. The OLED reveals maximum power efficiency (PE), current efficiency (CE) and external quantum efficiency (EQE) 74 lmW-1, 70 cdA-1 and 18.5 %, respectively, with doping 20 wt % CuI into CuPC, while PEDOT:PSS based OLED exhibits PE of 48 lmW-1, CE of 49 cdA-1 and EQE of 14 %. The enhancement of PE, CE and EQE of 33.3, 34.6 and 32%, which may be attributed to the optimized doping ratio of the CuPC and the CuI showing improved hole transport ability, optical properties, surface roughness, and the reduced hole injection barrier. Our outcomes deliver an efficient tactic to replace PEDOT:PSS and enhance the performance of OLED by incorporating CuI as dopants into CuPC.

Organic light emitting diodes (OLEDs) are emerging key technology for full-color flat-panel displays and high-quality solid-state lighting sources. OLEDs have encountered various challenges to achieve energy-saving highly-efficient OLEDs due to a limitation in the thermal evaporation process. In highly efficient OLED devices, the hole injection/transport layer is a key factor to fabricate stable and efficient devices. Transition metal oxides have promising potential, due to their balanced charge injection and efficient carrier mobility. Herein, we demonstrated a solution-processed efficient yellow phosphorescent OLEDs with tungsten trioxide (WO3) hole-injection/hole-transport layer (HIL/HTL). The electroluminescent characteristics of PEDOT: PSS and WO3 based devices were studied with the structure ITO/PEDOT: PSS or WO3/CBP: PO-01/TPBi/LiF/Al. The WO3 based OLEDs exhibits maximum luminance of 10230 cd m-2, the power efficiency of 35.9 lm W-1, current efficiency 51 cd/A, and external quantum efficiency of 17.4 %. Moreover, the resultant device also displays 45% higher power efficiency as compared to other counterparts. The higher device performances of OLED device may be attributed to the effective hole transporting ability, balanced charge carrier injection in the emissive layer, and non-acidic characteristic of HIL. Analysis of results illustrates an alternative tactic based on tungsten trioxide as a substitute of PEDOT: PSS for solution processable energy-saving OLEDs.