Fabrications and device characterizations of inverted organic solar cells using polyethylenimine ethoxylated cathode interlayers and graphene cathodes
Date Issued
2014
Date
2014
Author(s)
Yeh, Chih-Ting
Abstract
In this study, we fabricate bulk heterojunction organic solar cells with polyethylenimine ethoxylated (PEIE) cathode interlayers and graphene cathodes. The performance of solar cells is systematically investigated.
The solar cells investigated in this thesis are fabricated in inverted structures with P3HT:ICBA as the active layer. First, we optimize the PEIE cathode interlayer, and the efficiency can reach 5.23% after optimization. The PEIE layer lowers the ITO work function (WF) , and can be used as a cathode . Then, the AZO layer is introduced in the devices along with PEIE to modify the WF and make the active layer junction smoother and the PCE achieves 5.72%. UPS measurements on PEIE-coated ITO or AZO film show the consequence of WF modification. AFM measurements were also carried out to figure out the morphology of these layers.
In addition, we fabricate solar cells using graphene as cathodes. We transfer three layer graphene with cesium fluoride (CsF) interlayer doping to make the graphene WF lower and is more favorable as cathodes. Due to graphene’s hydrophobic nature, we use oxygen plasma treatment to improve the hydrophilicity of graphene. After this treatment, the follow-up AZO film quality can be enhanced. The PCE of graphene-cathode solar cell is 3.22%, which is still a little bit lower than that of ITO-based device. The high sheet resistance and the inadequate hydrophilicity are the two main reasons for the low PCE of the graphene solar cells. However, these works still make the graphene as cathodes realized for the first time.
Subjects
有機太陽能電池
倒置結構
乙氧基聚乙烯亞胺陰極介面層
石墨烯陰極
Type
thesis
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