The Effect of Thickness of Active and Buffer Layers on Performance of Green Organic Light Emitting Diode

In this paper, green organic light emitting diodes (OLED) with the structure of ITO/MoO3/TPD/Alq3/LiF/Al were designed and fabricated using thermal evaporation technique. The effects of thickness of the Alq3 as the electron transport and emitter layer, TPD as the hole injection layer, and MoO3 which plays the role of the buffer layer of hole injector, were investigated on the performance of these diodes. In order to obtain the best performance of the proposed structure, by considering the appropriate range of the thickness of the layers, the optimum thickness of the Alq3, TPD and the buffer layer of MoO3 is determined in the used structure and the function of each of them was analyzed. After measuring the photometric parameters of the fabricated diodes, the optimized thickness of 45 nm for Alq3, 40 nm for TPD, and 15 nm for MoO3 were determined. By optimizing the thickness of the layers, the efficiency of the diode was improved due to the balance of the distribution of electrons and holes in the interface of emissive and hole transport layers. From the current density-voltage characteristic curve, the threshold voltage for the optimized diode was determined to be 3.9 (V), which is an important value in organic light emitting diode. Also, according to electroluminescent results for the optimized organic light emitting diode, maximum current efficiency was about 2.1 (cd/A), the maximum luminescence was 7530 (cd/m2) and maximum radiation was measured at the wavelength of about 530 nm.