Highly transparent micro-patterned protective coatings on polyethylene terephthalate for flexible solar cell applications

Abstract

Degradation of the performance and efficiency of organic solar cells (OSC) due to surface damage, caused by exposure to harsh environments, continues to be a major problem. Therefore, protective coatings must be developed that minimize damage to the outer surface of OSCs, without compromising their transparency and flexibility. For this purpose, ultra-thin, micro-patterned, single/bi-layer coatings comprised of H-free diamond-like-carbon (DLC) and indium tin oxide (ITO) were fabricated. The coatings were deposited onto polyethylene terephthalate (PET) substrates, using magnetron sputtering. The goal of the micro-patterning was to improve the wear resistance of the coatings, while maintaining the high optical transparency of PET. Optical properties, wear resistance, erosion resistance, and flexibility of the coatings were investigated. Furthermore, the performance of a pre-fabricated OSC with and without the proposed protective coating before and after the wear and erosion tests was investigated. The experimental results demonstrated that the wear resistance and transparency (of the single layer micro-patterned DLC coating), was superior to both bi-layer and continuous DLC coatings. The micro-patterned DLC coating caused very little change in transparency (less than 1.7% reduction in the visible spectrum), and reduced the wear rate (mm3/N·mm) of PET by ∼75%. The erosion resistance of the PET was improved, and its degree of flexibility was unaffected. Overall, the results of OSC performance analysis demonstrated the functionality and potential application of the proposed micro-patterned protective coating for flexible solar cells.