Swiss researchers tout record-efficient CdTe cells for R2R

Researchers from the Swiss Federal Laboratories for Materials Testing and Research (EMPA) near Zurich have produced cadmium telluride (CdTe) thin-film solar cells with a record 12.4% efficiency, made with a low-temperature process compatible for roll-to-roll manufacturing.

August 21, 2009 –  Researchers from the Swiss Federal Laboratories for Materials Testing and Research (EMPA) near Zurich have produced cadmium telluride (CdTe) thin-film solar cells with a record 12.4% efficiency, made with a low-temperature process compatible for roll-to-roll (R2R) manufacturing.

The flexible CdTe thin-film cells (measuring Voc= 823 mV, Jsc= 19.6 mA.cm-2, FF= 76.5% under standard AM1.5 illumination) were made on a lightweight polymer (polyimide) film using a low-temperature (<450°C) vacuum evaporation process to grow the layers, and subsequent annealing in air. The indium tin oxide (ITO) layers used in previous 11.4% efficient cells was replaced with a bi-layer of ZnO/ZnO:Al as a transparent electrical contact; this improved process yield and reproducibility, and is cheaper than expensive ITO, they noted.

Key to the work was development of low-temperature and compatible processes, as well as reducing optical and electronic losses limiting cell performance. All the process steps of this flexible CdTe solar cell are compatible with continuous in-line processing and can be transferred to R2R manufacturing of large-area solar modules with high deposition speed, the researchers note.

Results were presented during the recent SPIE Optics and Photonics Conference in San Diego, August 2-6.

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