Degradation studies of flexible optoelectronic device electrodes

Abstract

Theodros S. Bejitual Flexible transparent electrodes offer significant advantages, such as low cost, large area, light weight, conformability, robustness, and ease of roll-to-roll manufacturing and processing. They are routinely used as anodes in organic light emitting diodes, liquid crystal displays, touch panels, solar cells, solid state lightings, energy harvesting, and biomedical applications to name a few examples. However, the electromechanical and corrosion issues involved when the device is stressed and/or in contact with acid containing components both during manufacturing and/or in service conditions have to be investigated in order to improve, and predict reliability. The primary objective of this research is to investigate the degradation behavior of two types of flexible transparent conducting layers, indium tin oxide (ITO) and carbon nanotubes (CNT) on polymer substrates, under electromechanical and corrosion conditions. Changes in electrical resistance and morphological features of these thin film electrodes are investigated using experimental methods such as corrosion, bending, fatigue, bending-corrosion, fatigue-corrosion, and tribo-corrosion. Such methods attempt to simulate induced stresses during manufacturing and/or in-service conditions. Studies on both patterned and non-patterned surfaces are performed. Furthermore, finite element modeling is used to simulate the stress/strain distribution of the electrodes under various deformation modes. The effects and synergies of corrosion, applied strain, film thickness, and number of bending cycles on the electrical and structural integrity of the electrodes are investigated using design of experiment methods. During this project it was found that CNT-based electrodes outperform their ITO counterparts under fatigue in corrosive environments. However, for most high current electronic devices ITO still needs to be utilized. During combined fatigue corrosion experiments of ITO-coated polymer electrodes externally applied strain was found to be the most critical factor for degradation. Experimental analysis and modeling of thin film electrodes for flexible optoelectronics will aid towards the design of more reliable devices in the future.

The Effects of Corrosion, Fatigue, and Corrosion-fatigue of Multilayer Coated Polyesters for Flexible Electronics Applications

“…Bejitual [26] reported that, in the bending fatigue tests on a single ITO (200 nm) film coated on a PET substrate, the change in the electrical resistance was 50% at 150000 cycles for 0.6% strain. This means that the ITO/Ag-alloy/ITO film shows superior flexibility in compression to a single ITO layer.…”