New ORNL solar cell technology cranks up efficiency


OAK RIDGE, Tenn., April 29, 2011 – With the creation of a 3-D nanocone-based solar cell platform, a team led by Oak Ridge National Laboratory’s Jun Xu has boosted the light-to-power conversion efficiency of photovoltaics by nearly 80 percent.

The technology substantially overcomes the problem of poor transport of charges generated by solar photons. These charges — negative electrons and positive holes — typically become trapped by defects in bulk materials and their interfaces and degrade performance.

“To solve the entrapment problems that reduce solar cell efficiency, we created a nanocone-based solar cell, invented methods to synthesize these cells and demonstrated improved charge collection efficiency,” said Xu, a member of ORNL’s Chemical Sciences Division.

The new solar structure consists of n-type nanocones surrounded by a p-type semiconductor. The n-type nanoncones are made of zinc oxide and serve as the junction framework and the electron conductor. The p-type matrix is made of polycrystalline cadmium telluride and serves as the primary photon absorber medium and hole conductor.

With this approach at the laboratory scale, Xu and colleagues were able to obtain a light-to-power conversion efficiency of 3.2 percent compared to 1.8 percent efficiency of conventional planar structure of the same materials.

“We designed the three-dimensional structure to provide an intrinsic electric field distribution that promotes efficient charge transport and high efficiency in converting energy from sunlight into electricity,” Xu said.

Key features of the solar material include its unique electric field distribution that achieves efficient charge transport; the synthesis of nanocones using inexpensive proprietary methods; and the minimization of defects and voids in semiconductors. The latter provides enhanced electric and optical properties for conversion of solar photons to electricity.

Because of efficient charge transport, the new solar cell can tolerate defective materials and reduce cost in fabricating next-generation solar cells.

“The important concept behind our invention is that the nanocone shape generates a high electric field in the vicinity of the tip junction, effectively separating, injecting and collecting minority carriers, resulting in a higher efficiency than that of a conventional planar cell made with the same materials,” Xu said.

Research that forms the foundation of this technology was accepted by this year’s Institute of Electrical and Electronics Engineers photovoltaic specialist conference and will be published in the IEEE Proceedings. The papers are titled “Efficient Charge Transport in Nanocone Tip-Film Solar Cells” and “Nanojunction solar cells based on polycrystalline CdTe films grown on ZnO nanocones.”

The research was supported by the Laboratory Directed Research and Development program and the Department of Energy’s Office of Nonproliferation Research and Engineering.

Other contributors to this technology are Sang Hyun Lee, X-G Zhang, Chad Parish, Barton Smith, Yongning He, Chad Duty and Ho Nyung Lee.

UT-Battelle manages ORNL for DOE’s Office of Science.

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7 Responses to New ORNL solar cell technology cranks up efficiency

  1. Dave Mann May 3, 2011 at 9:40 am #

    This is all well and good but when will we be able to purchase these items at a reasonable price? This is very much like the Compressed Natural Gas (CNG) fuelled automobiles upon which Honda has a monopoly. One of those “you can’t get there from here” problems for the ordinary Joe Sixpack consumer like I am.

  2. DIY Solar Power System May 2, 2011 at 5:01 am #

    I love articles about the increase in solar technology efficiency. There are massive developments just about every week in the industry. It bodes well for the future.
    Until solar power is installed in every newbuilt house as a matter of routine, there will not be much change to the horrific, damaging footprint that humanity’s callous energy production methods are leaving on the planet.

  3. Malcolm Greenstuart May 2, 2011 at 4:12 am #

    I think the number must be an improvement from 18% to 32%, not 1.8 to 3.2.
    Is that right.
    And the cost is importartant too. I hope it can be done economically.

  4. Hogmanay April 30, 2011 at 7:05 am #

    Jello.

  5. Evanism April 30, 2011 at 4:19 am #

    The title is very misleading. It would be cool if efficiency was 80%, not improved by 80. I had to think about what commercial efficiencies were…. Nicer if the article were more upfront

  6. Cellar April 29, 2011 at 2:53 pm #

    Concur with mr. Landis. Wake me when this helps break the 60% efficiency barrier. Not to say that this isn’t interesting, but the title does oversell it.

  7. Geoffrey A. Landis April 29, 2011 at 1:52 pm #

    It’s a nice minor advance in technology, but the headline is so misleading as to be incorrect.
    The best solar cells today have conversion efficiency of around 33%. Even the commercial cells used for terrestrial applications are over 15% efficient. It’s interesting to show that you can increase performance of a 1.8% efficient cell to 3.2%, but this really is work that improves materials that are very far from the state of the art.

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