Changing the Type of Oxide Used in Photovoltaic Cells Makes Films More Efficient
This graded transparent conducting oxide (G-TCO) improves the efficiency of thin film solar cells through a new design of the transparent conducting contact. Thin film solar technology is a more viable alternative energy solution than traditional solar, because it uses extremely small quantities of solar materials (one-millionth of a meter thick), enabling extremely low manufacturing cost. Three main types of thin solar cell technology are on the market: amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium deselenide (CIGS). CIGS already have reached 20 percent cell efficiency, the highest of the three cell types. Researchers at the University of Florida have discovered a way to enhance the efficiency even more by using a graded transparent conducting oxide combined with the CIGS instead of the transparent conducting oxide (TCO) used in available technologies. A solar device absorbs incoming light energy and outputs electric energy. Both forms of energy are affected by the TCO. Incoming light is dimmed after passing through the TCO – the first loss. That light is converted to electricity. Afterward, the electricity will pass through the same TCO and be reduced by electric resistance – the second loss. The double-loss of the TCO makes optimization important – which is essentially to balance the optical loss (dimming) with resistance (electric energy) loss – tuning the thickness and doping. By switching to a graded TCO, researchers achieve a mode of TCO electrical and optical performance that is outside the capabilities of an optimized flat TCO, resulting in a more effective source of solar power.
The graded transparent conducting oxide (G-TCO) technology is expected to improve the efficiency of commercial thin film solar products.
- Employs lower series resistance and better optical transparency, providing a more effective source of solar power
- Thinner film solar cell increases light absorption, improving efficiency
- CIGS combined with G-TCO nearly eliminates need for the known toxin, Cadmium, protecting the environment
- Substrate has smooth surface and a high chemical stability, enabling support for razor-thin layers of semiconductor
This thin, flexible solar cell made of copper indium gallium selenide (CIGS) can be placed nearly anywhere for maximum sun exposure. It includes a graded transparent conducting oxide (GTCO) layer, a triangular shape that has an advantage over flat transparent conducting oxide layer TCO used in available technologies: G-TCO’s thickness is proportional to the electric current per unit area from the center to the contact edge. The thickness of the G-TCO increases from the distal to the proximal end, where current is collected by a metal grid. In a thin film photovoltaic cell using the G-TCO, the ratio of maximum attainable power is greater than that of an equivalent cell that uses a flat TCO electrode. The use of the graded effect generates a more efficient photovoltaic cell.