Verification Of The Current-voltage Characteristics Of P-n Junction In Polymer Light-Emitting Electrochemical Cells

A polymer light-emitting electrochemical cell (LEC) offers an alternative approach to achieving electroluminescence (EL) from conjugated polymers. Unlike a polymer light-emitting diode (PLED), the operation of an LEC involves in situ electrochemical doping and the formation of a dynamic p-n junction. The light-emitting electrochemical cell (LEC) combines the novel electrochemical properties of conjugated polymers with the ionic conductivity of polymer electrolytes. In contrast to LED, LECs offer significant advantages over polymer LEDs, such as low operating voltage, high EL efficiency. Thin film sandwich structure is usually used for LECs. A thin film of a polymer blend (conjugated polymers + electrolyte) is sandwiched between two thin metal electrodes, one of which is often ITO. LEC operates with an in situ electrochemical doping mechanism, finally a p-n junction is found. A LEC device is, in principle, insensitive to the work functions of metal contacts because the polymer/ electrode interfaces can form ohmic contacts after the electrochemical doping of the EL polymer. The film thickness is about 200nm in this typical sandwiched structure LEC, which has only one p-n junction. As reported that the LEC in planar structure which enlarged the interelectrode spacing had been demonstrated. Later simultaneous formation of multiple (up to thousands) light-emitting p-n junctions in a device structure were researched by introducing tiny metallic particles or strips into the polymer film.There is an argument about the mechanism of the LEC in the world, in this paper, a sandwich light-emitting electrochemical cell (LEC) has been fabricated with film thickness of 1.7-2um .Then metallic particles (Al, a nominal size of average 18nm in diameter) are mixed into an electrolyte \electroluminescent composite polymer film, and light-emitting p-n junctions are formed in situ by electrochemical p- and n-doping randomly. Mixing Al particles into an electrolyte electroluminescent composite polymer film has a certain degree of influence upon the current and brightness etc. Scanning electron microscopy (SEM) imaging of the polymer films shows both small particles and the Al as aggregates. A physical model can be established through the imaging. Striking details of the p-n junction, the bulk resistance in LEC have been verified by the application of Matlab. Hence, it is reasonable to elucidate the mechanism of junction formation in these devices by using the modified Shockley function of p-n junction in semiconductor physics. The mechanism and the p-n junction formation of LECs are further verified from the electrical properties.In this work, frozen p-n junction LECs have been fabricated preliminarily. The property of the frozen p-n junction such as the frozen junction is a static junction has been researched. And the affect of the temperature on the ionic mobility has been simply researched. Simultaneously, this thick (micrometer) sandwich device structure containing metallic nanoparticles, and below the glass transition temperature (T_g) resulting frozen p-n junction, it is possible to achieve both a large device current and a large number of p-n junctions which will result in more efficient light emission and photovoltaic conversion.