Electrode Modification And Characterization Of Organic Optoelectronic Devices

The photovoltaic devices based on organic materials, with the characteristics of low-cast and good flexibility, have received widespread attention by researchers. The application of organic electroluminescent device in the field of displayer has already reached the practical standard at this stage. However, the application on the illumination field still leaves much to be improved. After several decades developments, the photoelectric conversion efficiency of organic solar cells has exceeded10%and also been close to practical standards.The ability of carriers injection of OLED is associates with chemical and physical properties of cathode and anode, such as the work function of electrode, the surface morphology, the surface wettability etc. A lot of modification methods, such as, oxygen plasma, the introduction of a buffer layer and so on, were proposed to improve the carriers injection capability. In this paper, the ITO electrode was modified by electrochemical methods, which has simple, low-cost and more practical advantages.Firstly, we did a electrochemical treatment to ITO with HF acid solution whose concentration was2×10-2mol/L, it caused the work function increased to0.5eV, and the electrochemical treatment won’t sacrifice ITO’s surface roughness and transmittance function of visible light. Because of the surface reaction between F-ion and ITO, there will be a dipole layer on the surface of the ITO; synchronously, the content of oxygen vacancies of ITO surface increased, these two phenomenons will improve ITO’s work function. Using this electrode, a maximum external quantum efficiency (EQE) of26.0%(91ed/A,1021m/W) is obtained, which is12%higher than that of a device using the oxygen-plasma-treated ITO. Fluorination also increases the transparency in the near-infrared (NIR) region.Secondly, we use the concentration of3.7×10-4mol/L NH3·H2O electrochemical treatment of ITO, then the work function decreases0.44eV, electrochemical treatment on ITO surface roughness has no effect, and the influence of transmittance is very small. In addition, NH4+ion and ITO surface reaction can generate a ITO dipole layer and reduce the content of oxygen vacancies on the surface of ITO. These two phenomenons make the ITO function decrease. By using this electrode, a maximum external quantum efficiency (EQE) of2.54%(12.74cd/A,8.611m/W) is obtained, which is8times higher than that of a device using as-cleaned ITO.Finally, we produced an organic solar cell with inverted structure by NH4-ITO, which was treated by a concentration of3.7×10-4mol/L NH3·H2O. Compared to the inverted device without ITO treatment, the photoelectric conversion efficiency increased by34%.