Enhanced Current Efficiency of OLEDs with NPB (5 nm)/TCTA (5 nm) Multilayers Sandwiched Between ITO (Anode) and Alq₃ (50 nm)/LiF (1 nm)/Al (Cathode)

Abstract

In the present work, organic light emitting diodes (OLEDs) with an ultra-thin layer of NPB (5 nm)/TCTA (5 nm)/NPB (5 nm)/TCTA (5 nm)/Alq₃ (50 nm)/LiF (1 nm) are fabricated using physical vapor deposition at 1.33 × 10⁻⁹ kPa pressure. Each time the synthesized layer was placed on top of the previous layer. Up to five layers were formed between the anode (ITO) and Alq₃ (50 nm)/LiF(1 nm)/the cathode (Al) layers, and each time the properties of the diode were investigated using GPS 132A, I–V curves and atomic force microscopy and by analyzing the luminance–voltage (L–V) and current density–voltage (J–V) curves. The obtained results indicate that sample b (ITO/NPB = 5 nm/TCTA = 5 nm/NPB = 5 nm/TCTA = 5 nm/Alq₃ = 50 nm/LiF = 1 nm/Al = 100 nm) due to lower threshold voltage (8 V) (lower energy consumption), lower current density (56 A/m²), better brightness (L = 140 cd/m²) and higher current efficiency (2.5) than samples with one-, two-, three- and four-NPB = 5 nm/TCTA = 5 nm layers, which can be suggested in future generations of OLEDs.