Conventionally solar cells are fabricated on crystalline semiconductor wafers which yield high-performance but are expensive. A cheaper alternative to wafers are polycrystalline or amorphous semiconductors which can be directly deposited on a low-cost substrates like glass, plastic, or steel. If the substrates are flexible, e.g. plastic or steel foil, the devices can be fabricated in a continuous roll-to-roll process, reducing costs even further. Flexible steel is a great platform for thin-film devices because it is cheap, earth-abundant, scalable, and can withstand the high temperatures required in semiconductor processing.
Unfortunately, integrating semiconductors on steel is a challenge for two reasons: 1. Semiconducting thin-films deposited on top of steel get contaminated with iron. Iron causes defects in the semiconductor leading to severe loss in efficiency. 2. Semiconductor thin-films deposited on steel tend to be polycrystalline with very small grain sizes, severely limiting the efficiency of solar cells.
The goal of this project is to demonstrate solutions for these two specific issues. The diffusion of iron is reduced by incorporating an “iron-diffusion-barrier” layer between steel and semiconductor overlayer. While the grain-size of the semiconductor thin-film in enhanced by using directional laser-crystallization.