Production, Characterization and Stability of Organic Solar Cell Devices

Despite the fact that the field of organic photovoltaics (OPVs) is in a rapid progress, organic solar cells continue taking backstage roll in the growing markets of various solar technologies. The main challenge of the field is to develop devices that would possess all the optimal properties required for efficient, stable and cheap solar cells, i.e. devices that can deliver high photoconversion efficiencies and long lifetimes and can be efficiently produced in large scales using roll-to-roll coating technologies. This dissertation is primarily devoted to the issues of photoconversion efficiency and device lifetimes. In particular, descriptions of some practical approaches for different device designs and processing of active layer for typical small scale OPV devices were presented. The emphasis was put on some optimizing techniques for processing of active layer that can significantly improve the device photoconversion efficiency. The techniques were further applied for manufacturing and characterization of solar cell devices based on various materials. In particular, a number of thermocleavable polymers were studied and devices based on such materials were produced and characterized. The applicability of such materials in photovoltaic devices was shown and further challenges were discussed. Another task of this work was to manufacture and study inverted device structures and compare their properties with normal structure based devices. Device based on both structure were successfully produced with same level of performance in terms of photoconversion efficiency, yet with totally different stability performance. As another task, metal oxides, such as MoO3 or V2O5 were studied in solar cell devices as buffer layers instead of PEDOT:PSS. Although the device efficiencies obtained with metal oxides were inferior to PEDOT based device, it was shown that such materials can possibly improve the device efficiency if the processing of the layers is optimized. The final part of the work is devoted to the issue of stability. In particular, a setup comprising an atmospheric chamber was presented for efficient lifetime evaluation of OPV devices and examples of exploitation of the setup were shown. Lifetime studies of various thermocleavable polymers were carried out and compared to commonly used thiophene based polymers. Comparative degradation studies were carried out for normal and inverted device structures under different atmospheric conditions, which revealed different degrading features for different structures. While the normal geometry devices were rather stable in oxygen and rapidly degraded in humid environment, the inverted devices showed strong degradation in oxygen, but stayed rather stable in high humidity.