Breaking mechanism of indium tin oxide and its effect on organic photovoltaic cells

Indium Tin Oxide (ITO) is one of the most used anode materials in organic solar cells. ITO is a brittle material, however, in roll-to-roll manufacturing plants and final applications material flexibility is beneficial. This study examines the flexibility limits of ITO in applications manufacturing photovoltaic cells. First, ITO was bent using different cylinders to achieve different sample bending curvatures and thus different stages of breaking. Next, the conductivity of ITO was measured and surface topology was profiled. As a result, it was discovered that samples start to break even with low bending curvatures, and while no changes are detected in the surface profile, conductivity starts to decrease. When the cracks start to appear on the surface of ITO, a specific radius of curvature is discernible. In this critical bending curvature resistance and its relative standard deviation start to increase faster. Optical profilometer examination revealed that the cracks reach the ITO surface at the same moment. After this critical bending curvature, clear positive correlation was observed between the conductivity and the number of cracks. To test the effect of cracked ITO on the performance of solar cells, solar cells were produced on top of the cracked ITO layer. The measurements showed that cracks did not decrease the performance of solar cell. This fact supports the use of ITO-based organic photovoltaic cells in applications where flexibility is required as well as in roll-to-roll manufacturing.