載子陷阱在高分子發光二極體內的效應

Abstract

這篇論文主要探討載子陷阱在高分子發光二極體內的效應。在只有電子的元件裡,陷阱會對電子的電流有顯著的影響.加入較多的陷阱,電子的電流會愈小,而且電子電流對電場的依靠會愈大.除了電流之外,陷阱也會增加元件的時間尺度. 在雙載子的元件,因為陷阱扮演著負電荷的角色,所以有助於電洞的注入,因而增加了總電流.除此之外,陷阱的增加也會增加電子電動在陰極的復合率,主要是由於增加陷阱,會導致電子與電動的濃度在陰極的地方較平衡,因而增加了復合率.相對地,在陽極的地方復合率就會減少.同樣的,陷阱也會增加雙載子元件的時間尺度,而整個元件的時間尺度在千分之一秒是有可能的.

This thesis represents the effects of traps in polymer light-emitting diodes. In electron only devices,the electron conduction in polymer is strongly reduced by the presence of traps. Putting more traps, we find stronger electric field dependence in electron current density. If we apply larger voltage, because more traps are filled, electron current is approaching to the hole current density. Traps not only reduce the current in electron only devices, but also increase the time required for device reaching the steady state. In our simulation, we represent that traps contribute to the time delay in devices. In double carrier devices, because of Coulomb force, putting more traps contribute to the injection of hole current density and total current density. In our simulation, two times total current density is possible. We consider the recombination process as bimolecular and using Langevin form for recombination coefficient. Because of the imbalance between electron and hole current density, putting more traps result in lower efficiency in polymer light-emitting diodes. If we put traps more than 1019cm¡3, the recombination efficiency can be suppressed to one-half. We observe that when the trap density is one-tenth of the free electron density without traps, the efficiency begins to go down greatly. Similarly, we consider the time scale in bipolar devices.