Nanowire arrays improve performance of thin-film solar cells

Editor's note: The Center for Nanoscale Science and Engineering (CeNSE) is a multidisciplinary group of faculty, students, and staff at the University of Kentucky and a cutting-edge research facility to study and develop materials and devices at the nanoscale. UK faculty members from a wide variety of disciplines along with graduate research assistants, post-doctoral associates, and a number of undergraduate students use CeNSE equipment and facilities. CENSE is run by Vijay Singh and is located in the ASTeCC campus incubator.

(April 19, 2011) —Nanotechnology offers a promising path to high-efficiency and low-cost next-generation solar cells. As the field matures and developers gain a deeper understanding of size effects, the efficiency values achieved by nanostructured designs are expected to surpass traditional devices by wide margins.

Researchers at the University of Kentucky, US, have developed two novel device configurations for thin-film CdS-CdTe solar cells, where the traditional CdS window layer is replaced by nanowires of CdS embedded in an aluminum oxide matrix or free standing, as shown in the figure above.

A 26.8% improvement in power-conversion efficiency over the traditional device structure is expected to result from (i) enhanced spectral transmission of sunlight through the window layer and (ii) a reduction in the junction area/optical area ratio, which reduces the total number of interface states at the heterojunction, thus yielding higher Voc.

In initial experiments, the team fabricated nanostructured devices based on the two designs and obtained Voc, Jsc, FF and efficiency values of 705 mV, 25.3 mA/cm2, 36.4% and 6.5%. Process optimizations for higher performance are in progress.

Full details can be found in the journal Nanotechnology.

About the author

The study was conducted by the research group of Vijay Singh, who conceived and guided the project at the Center for Nanoscale Science and Engineering (CeNSE), and the Department of Electrical and Computer Engineering (ECE) at the University of Kentucky, US. Piao Liu was a PhD student at the University of Kentucky and is now a member of the Physics Department at Brooklyn College, City University of New York. Vijay Singh is the Robinson Chair Professor and the Director of CeNSE; Carlos Jarro is a PhD student; Suresh Rajaputra is a senior research scientist; and all three are in the ECE Department at the University of Kentucky. The team's research interests are in the area of nanostructured devices with applications in solar cells and sensors.