InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit
- Jesper Wallentin1,
- Nicklas Anttu1,
- Damir Asoli2,
- Maria Huffman2,
- Ingvar Åberg2,
- Martin H. Magnusson2,
- Gerald Siefer3,
- Peter Fuss-Kailuweit3,
- Frank Dimroth3,
- Bernd Witzigmann4,
- H. Q. Xu1,5,
- Lars Samuelson1,
- Knut Deppert1,
- Magnus T. Borgström1,*
- 1Solid State Physics, Lund University, Box 118, 22100 Lund, Sweden.
- 2Sol Voltaics AB, Ideon Science Park, Scheelevägen 17, 22370 Lund, Sweden.
- 3Fraunhofer ISE, Heidenhofstrasse 2, D-79110 Freiburg, Germany.
- 4University of Kassel, Wilhelmshoeher Allee 71, 34121, Kassel, Germany.
- 5Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China.
- ↵*To whom correspondence should be addressed. E-mail: magnus.borgstrom{at}ftf.lth.se
Improving Nanowire Photovoltaics
In principle, solar cells based on arrays of nanowires made from compound inorganic semiconductors, such as indium phosphide (InP), should decrease materials and fabrication costs compared with planar junctions. In practice, device efficiencies tend to be low because of poor light absorption and increased rates of unproductive charge recombination in the surface region. Wallentin et al. (p. 1057, published online 17 January) now report that arrays of p-i-n InP nanowires (that switch from positive to negative doping), grown to millimeter lengths, can be optimized by varying the nanowire diameter and length of the n-doped segment. Efficiencies as high as 13.8% were achieved, which are comparable to the best planar InP photovoltaics.
Abstract
Photovoltaics based on nanowire arrays could reduce cost and materials consumption compared with planar devices but have exhibited low efficiency of light absorption and carrier collection. We fabricated a variety of millimeter-sized arrays of p-type/intrinsic/n-type (p-i-n) doped InP nanowires and found that the nanowire diameter and the length of the top n-segment were critical for cell performance. Efficiencies up to 13.8% (comparable to the record planar InP cell) were achieved by using resonant light trapping in 180-nanometer-diameter nanowires that only covered 12% of the surface. The share of sunlight converted into photocurrent (71%) was six times the limit in a simple ray optics description. Furthermore, the highest open-circuit voltage of 0.906 volt exceeds that of its planar counterpart, despite about 30 times higher surface-to-volume ratio of the nanowire cell.
- Received for publication 1 October 2012.
- Accepted for publication 17 December 2012.
