By William H. Marks
The inefficiencies of previous generation solar cells are rapidly becoming a thing of the past. In collaboration with the UCLA California NanoSystems Institute and Sumitomo Chemical of Japan, researchers at the UCLA Henry Samueli School of Engineering and Applied Science have created a "tandem" solar cell that increases efficiency to a certified 10.6% by capturing energy in multiple spectra.
The solar cell, built by combining a front cell with a high band gap material, specifically designed interlayer, and back cell with a low band gap material, allows for the increase in efficiency by increasing output voltage while maintaining current, a feat that required specially matched band-gap materials investigated for their chemical properties.
These organic polymers, produced at low cost even in high volumes, allowed the team, led by Yang Yang, to combine single cells into a "tandem" cell to harness the additional efficiency, occupying the same footprint but slightly more depth to allow room for both of the "tandem" cells. The packaged cells take advantage of multiple wavelengths within solar radiation to use the received sunlight more efficiently. This had not previously been possible since material and band gap matching are imperative for the "tandem" cell to work properly and actually increase efficiency. Two separate, random cells cannot be simply combined together to increase efficiency, as evidenced by prior research in the field.
Sumitomo Chemical of Japan provided a new polymer material that absorbs the infrared and allows the cell to take advantage of that spectrum as well, which increased the efficiency to 10.6% from 8.62%, a previous record set by the "tandem cell" without the Japanese polymer, which relied on different absorption bands in the "tandem" structure. With the current technology, they hope to commercialize this product with an ultimate goal of 15% efficiency within the next several years, a very promising opportunity, given the huge amount of money spent on solar energy each year already.