Researchers Find That Two Thin Film Layers Increase Solar-Cell Efficiency

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Although solar cells have improved over the years, thin film solar cells are still less efficient than crystalline solar cells, which are too expensive for commercial use. This is part of the downsides we reviewed in the pros and cons of solar energy. After experimenting with different materials and solar cell construction, a team of researchers has found that using two thin films of different materials can create solar cells that are both affordable and efficient. In fact, this new idea allows the solar cells to have about 34% efficiency, which is about 10% more efficient than the current models.

Interestingly, solar cells appear to be simple devices. They include a top layer and an energy conversion layer. The sunlight falls on the clear top layer so that it can be converted into energy in the energy conversion layer, where the light is absorbed. The energy conversion layer also produces negatively charged electrons and positively charged holes that move in opposite directions. After that, the opposite-moving particles transfer from a top contact layer to a bottom one, where the electricity is channeled out of the cell for us to use. The amount of electricity produced depends on the amount of sunlight collected and the conversion ability.

Traditionally, researchers approach solar cells from two sides: an optical side and an electrical side. The optical side looks at how the sunlight is collected by the panels, and optical researchers aim to optimize light capture. In contrast, the electrical side looks at how the light is converted into electricity, and electrical researchers optimize conversion to electricity. Though both researcher groups are effective at their jobs, they simplify the other side, which prevents them from optimizing both sides of a solar cell and decreases efficiency.

Study

Akhlesh Lakhtakia of Evan Pugh University and Charles Godfrey Bunder of Penn State, however, aimed to create a model that treated both the optical and electrical sides as equal. Through theoretical research and calculations, the researchers created this model to increase actual efficiency above 30% since anything lower will make little difference. The researchers have since published their findings in Applied Physics Letters.

Per their research, the researchers used two different absorbent materials in two different thin films, where the absorbent layer was nonhomogeneous in a special way. More specifically, they made the films from commercially available CIGS, copper indium gallium diselenide, and CZTSSe, copper zinc tin sulfur selenide. Each material has roughly the same lattice structure, which allows them to be grown on top of each other.

On their own, the efficiency of CIGS is about 20% while CZTSSe’s is only about 11%, which is not very efficient. Together, however, the two materials absorb different frequencies, which allows the combined efficiency to be around 34%, nearly 10% more efficient than single-layer solar cells.

Next Steps

Since Lakhtakia is a theoretician, he does not make thin films and the findings are purely theoretical. Instead, he creates mathematical models that test configuration material possibilities. So, the finding in this study is purely theoretical, meaning that it has not been tested on models in a laboratory. As a result, the next step for this study is to create two-layered films and experiment with them. The experiments will either back up or refute the theoretical findings, which will bring about the best answers concerning the solar panel construction efficiency.

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