An innovative method for accelerated photo-stability testing of novel thin film semiconductors for solar cell applications

• Applicant: Professor Dr. Christoph J. Brabec
• Subject Area: Synthesis and Properties of Functional Materials ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 317277494

Degradation mechanisms in optoelectronics such as solar cells occur either due to outer circumstances, e. g. water diffusion into the device over time, or due to intrinsic photo-degradation of the materials such as the absorber layer or electrodes. This intrinsic photo-degradation, due to illumination in the absence of oxygen and water, cannot be suppressed by smart device architectures or advanced packaging strategies. Measuring and successive understanding of the intrinsic degradation processes is, accordingly, a key for further increasing lifetime and reliability of solar systems.Within this project, we want to establish a novel method allowing the accelerated assessment of the photo-stability of optoelectronic materials and in particular of thin film semiconductors for solar applications. Our approach targets to speed up the photo-degradation time by a factor of several hundreds by using concentrated light, since current standard tests last several months. The novelty of the concept is to assess the degradation kinetics under concentrated illumination and well controlled temperature. In doing so, deep insight is gained into the various degradation mechanisms (under low illumination) of the optoelectronic materials or devices. The main technical challenge is to maintain precise control on the temperature for a wide range of illumination intensities. Accordingly, we will be able to separate temperature induced degradation from photo-induced degradation.To the best of our knowledge we are not aware of investigations trying to separate temperature induced degradation processes from photo-induced degradation of optoelectronic materials and use this insight into the processes to establish a method allowing to predict the maximal inherent lifetime of optoelectronic material in the shortest possible time. The proposed method certainly will have relevance to fields other than optoelectronics, such as optical coatings, however, due the background and experience of the investigator we will concentrate our first studies to semiconductors. Different materials, for example paints, chromophore films, spectral selective coatings or packaging foils, may be tested at a later stage.We will further focus our work on semiconductors with relevance for solar applications and, in particular, on materials related to thin film solar cells. A vast amount of novel promising, high performance thin film semiconductor materials is currently developed. Several hundreds of thousands of organic semiconductors were reported in the recent years, however, due to this huge number and long time periods required for lifetime testing, their inherent stability is largely unknown. A method allowing to investigate the intrinsic photo-stability of novel semiconducting materials in the shortest possible measurement time, days instead of months or years, is required in order to build correlations between the structure of the semiconductor and its intrinsic stability.

• DFG Programme: Research Grants