Electrical Behavior I-V Theoretical-Experimental OLEDS
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Electrical Behavior I-V Theoretical-Experimental OLEDS José M. Burgoa1, Cecilia González-Medina1, Ramón Gómez-Aguilar1 and Jaime Ortiz-López2 1
Unidad Profesional Interdisciplinaria de Ingeniería y Tecnología Avanzadas-IPN, Av. Instituto Politécnico Nacional 2580, México City, 07540. 2
Escuela Superior de Física y Matemáticas-IPN, Av. Instituto Politécnico Nacional Edificio 9, Unidad Profesional Adolfo López Mateos, Zacatenco, Mexico City, 07738.
ABSTRACT We develop a program (within MATLAB software environment) to numerically simulate current-voltage characteristics of a bilayer organic light-emitting diode (OLED). The program is based on the Poole-Frenkel and Schottky continuous quantum models which take into account the geometry of thin films and their emission parameters in the calculation of charge carrier and current density in organic materials. Simulations are performed for OLEDs with A/EML/C and A/HIL/EML/C architectures where A=anode, HIL=hole injection layer, EML=emissive layer and C=cathode. For EML we assume MEH-PPV and MDMO-PPV derivatives of poly-paraphenylene-vinylene (PPV) polymer semiconductor, and for HIL we use PEDOT:PSS. The results of simulation are compared with experimental results obtained from actual OLED devices constructed in our laboratory. For comparison we also use the commercial software SimOLED to simulate the devices under similar architectures. We find in general a fair agreement between the simulated and measured behavior except for a few orders of magnitude difference in the current. INTRODUCTION From a theoretical point of view, understanding of the behavior of organic light-emitting diodes with geometry ITO/MEH-PPV/Metal and ITO/PEDOT:PSS/MEH-PPV/Metal is possible through analysis based on the Schottky diffusion model and the Poole-Frenkel mobility model [1,2]. Theoretical modeling of the electrical response of OLEDs requires four essential parameters: film thickness of the organic semiconductor, work function of contacts, temperature of operation, and effective area of the electrodes. In this work we use the SimOLED (Sim4TEC) commercial software and our own MATLAB programs to model the behavior of OLEDs constructed in our laboratory. Since for the construction of OLEDs intervene parameters such as thickness, conductivity of the organic semiconductor and interface effects between the organic material and the contacts we consider eddy current models that provide a closer description of the behavior observed in actual physical devices. Typically, an OLED is comprised of: (a) a transparent cathode made of a material with high work function, usually indium-tin oxide (ITO); (b) an organic semiconductor active layer, usually deposited by spin casting this material dissolved in a volatile solvent, (c) an anode made of a metal or alloy (such as GaIn eutetic) of low work function. When excitons decay radiatively, the generated light emerges through the
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transparent region of the device. For conjugated polymers, singlet excitons are the only ones that decay radiatively. EXPERIME
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