Thin Films: Cadmium Telluride

Award-winning CdTe PV cells undergo weatherization to test their durability.

Cadmium telluride (CdTe) is an excellent semiconductor for solar cells because its bandgap of 1.4 electron-volts is matched nearly perfectly to the solar spectrum. The device structure also includes a very thin layer of cadmium sulfide that allows most sunlight to pass through to the CdTe layer. These characteristics provide the potential for high-efficiency modules with low-cost manufacturing processes. NREL currently holds the world-record conversion efficiency for CdTe of 16.5%.

Research on CdTe research focuses on several of today's challenges:

• Boosting efficiencies by, among other things, exploring innovative transparent conducting oxides that allow more light into the cell to be absorbed and that collect more efficiently the electrical current generated by the cell.

• Studying mechanisms such as grain boundaries that can limit the voltage of the cell.

• Understanding the degradation that some CdTe devices exhibit at contacts and then redesigning devices to minimize this phenomenon.

• Designing module packages that minimize any outdoor exposure to moisture.

• Engaging aggressively in both indoor and outdoor cell and module stress testing. For example, we propose to test thin-film modules in hot and humid climates.

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