An innovative method for accelerated photo-stability testing of novel thin film semiconductors for solar cell applications
Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
Final Report Abstract
It was already shown for low irradiances that temperature changes are correlated to solar cell degradation kinetics by an Arrhenius law. Accordingly, strong temperature dependence is also to expect at high irradiances and, thus, proper sample temperature control is absolutely inevitable in order not to confuse temperature and irradiance based degradation effects. We have developed a way to solve this problem with a new way of solar cell temperature determination and active sample cooling. It was shown that the measurement error of common temperature measurement techniques is huge which would also explain why accelerating degradation kinetics by using high irradiances is often attributed to increased sample temperatures in other reports. Accordingly, it was found that temperature management is of decisive importance at high irradiances in order to obtain reliable insight into the corresponding degradation experiments. This achievement enabled us to investigate the influence of the irradiance at a fixed temperature onto the degradation kinetics and in the same way degradation kinetics at high irradiances in dependence of the temperature was investigated. A novel method was developed within this project to perform stability testing of organic solar cells under highly concentrated illumination conditions. While others have used concentrated light sources before, we demonstrate that with conventional methods for temperature measurements and thermal management, the active layer temperature can be significantly higher than expected. By developing a novel temperature sensor which is integrated as a thin evaporated metal stripe directly on top of the active layer of the solar cell, precise temperature measurements of the active layer are possible. These measurements reveal a large thermal gradient inside the solar cell leading to a temperature difference of over 60°C (at 300 suns) between the active layer and the closest point which is accessible in conventional measurement techniques. This fact underlines the importance of proper temperature management in order to obtain reliable measurement data. The technical achievements enabled us to explore degradation kinetics at high irradiances and well controlled temperatures. Therefore, the well-known P3HT:PCBM system was used. It was found that the degradation process is well described by a stretched exponential law. Further, it was found that for material screening the short circuit current values of the solar cells deliver the most informative data. For this parameter a linear dependence of the degradation speed on the used irradiance was unveiled. This result is important concerning material comparisons as it means that the experimental time can be linearly reduced by increasing the irradiance. For the temperature dependence of the degradation kinetics at high irradiances an Arrhenius law was found. This finding underlines the importance of proper temperature management. All in all a laboratory and a procedure for fast material screening was successfully established. The presented achievements provide the possibility to quickly identify materials offering sufficient lifetimes and, thus, to boost material development towards more reliable devices. Besides organic PV materials, also other promising materials classes like perovskites or CIGS can be tested with the established setups in the future.
Publications
- Efficient Polymer Solar Cells Based on Non-fullerene Acceptors with Potential Device Lifetime Approaching 10 Years. Joule. 2019 3(1):215–26
X. Du, T. Heumueller, W. Gruber, A. Classen, T. Unruh, N. Li, C. J. Brabec
(See online at https://doi.org/10.1016/j.joule.2018.09.001) - Infrared Absorption Imaging of Water Ingress Into the Encapsulation of ( Opto- ) Electronic Devices. IEEE J Photovoltaics. 2019; 9(1):252–8
J. Hepp, A. Vetter, S. Langner, M. Woiton, G. Jovicic, K. Burlafinger, J. A. Hauch, C. Camus, H. Egelhaaf, C. J. Brabec
(See online at https://doi.org/10.1109/JPHOTOV.2018.2877883) - “A top-down strategy identifying molecular phase stabilizers to overcome microstructure instabilities in organic solar cells,”Energy Environ. Sci. 2019, 12, 1078
C. Zhang, T. Heumueller, S. Leon, W. Gruber, K. Burlafinger, X. Tang, J. D. Perea, I. Wabra, A. Hirsch, T. Unruh, N. Li, C. J. Brabec
(See online at https://doi.org/10.1039/c8ee03780a) - “Development of a High Irradiance Setup for Precisely Controlled Accelerated Photo-Degradation of Organic Solar Cells”, Dissertation an der Technischen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg, 2019
Burlafinger, Klaus
