Stefan Grob
Effect of morphology on molecular organic solar cells
Supervisor: Prof. Wolfgang Brütting [Experimental physics IV]
Date of oral examination: 01/27/2016
161 pages, english
This thesis provides a detailed look on the influence of changing morphologies on organic solar cell performance. Particular attention is paid on the comparison of crystalline and amorphous donor materials. These materials are chosen to be structurally similar so that upcoming differences can be almost completely attributed to morphological deviations. Moreover, a possibility to enhance the power conversion efficiency is presented by inserting an additional blocking layer beneath the donor. Again, there is a focus on the morphology. In particular, the question is answered whether and to what extent the morphology of the blocking layer influences the efficiency improvement. Typically,the morphology of organic thin films is already set after its preparation due to certain material properties. However, it is shown that a post-production process, annealing of the organic layers with solvent vapor, leads to a reorientation of the molecules and thus morphological changes. It is shown that such a treatment can improve several sub-processes within the overall charge generation process and thus also the efficiency of an organic solar cell. An alternative approach to improve organic photovoltaics is the application of tailor-made organic semiconductors. Therefore additionally, a detailed analysis of a new donor material is provided within the last section of this thesis.