針對有機太陽能電池我們建立了一套數值分析模型，發現使用不同功函數的金屬電極對開路電壓的變化影響不大。本文中提出兩種復合機制 : 注入能階較低情況下(歐姆接觸)，暗載子會從金屬端注入到半導體中且與光載子復合，這種復合機制即為 : 當載子移動率增加時,開路電壓會減少的主因。在高注入能階情況下(蕭特基接觸)，光載子與光載子之間的復合為主要的復合機制，在這種情況之下，即可藉著提高載子移動率，使得有機太陽能電池的效率增加。為了更深入的研究金屬功函數與有機太陽能電池效率之間的關係，我們利用模擬的方式去調整金屬功函數，發現暗載子復合與內建電場這兩種機制的平衡，使得開路電壓的變化幾乎為一常數。另外,我們亦提出理想的雙層結構，讓暗載子復合降低,使得被拆解載子有效的被收集，其效率相較於單層結構改善了高達60%。

The carrier recombination in organic solar cells is investigated by numerical modeling to explore the weak dependence of the open circuit voltage on the workfunction of the electrodes. Two recombination mechanisms are proposed. In ohmic contact with low carrier injection barrier, the photo carriers recombine pre-dominantly with dark carriers diffused from the electrode into the semiconductor and the recombination reduces open circuit voltage as mobility increases. The dark carrier induced recombination is the main limit of the power conversion efficiency for BHJ structure. As the barrier is increased such as Schottky barrier structure, the dark-carrier induced recombination is excluded so that photo-carrier induced recombination can be inhibited by increasing mobility and gives a better performance. As a given semiconductor, with decreased workfunction difference of the electrodes, reduces simultaneously the dark carrier recombination and the flat band voltage.The balance between these two opposite factors give a nearly constant open circuit voltage. Instead of using a Schottky contact, this study demonstrate an ideal bi-layer structure to reduce the dark-carrier induced recombination by separating carrier generation region from electrodes. Hence an improvement of power conversion efficiency over 60% is obtained compared with blending structures.

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