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The Solar Energy Materials Research Group is led by Senior Scientist Wladek Walukiewicz (PI) and Kin Man Yu (co-PI). Senior Staff Scientist Zuzanna Liliental-Weber is also associated with the program. The group is developing novel materials that address the immediate need for sustainable, clean energy sources. We are currently investigating Group III-Nitride semiconductors and highly-mismatched alloys for a number of energy-generating applications.  Moreover, we are also developing transparent conductors for full spectrum solar cell applications. The following are a few examples:

Full-spectrum Solar Cell

The newly discovered narrow bandgap of InN Eg~0.7 has extended the spectral range of the InGaN alloy system into the infrared region. That makes InGaN an excellent material for high-efficiency multi-junction (tandem) solar cells. As shown in the picture below, the bandgap of the InGaN alloy matches the solar spectrum (Air Mass 1.5) almost perfectly [1]...more >>


InGaN-Si hybrid tandem cell
  • No tunnel junction needed
  • Built on well-established Si solar cell technology

"Multiband" Solar Cell

The intermediate band acts as a “stepping stone,” allowing absorption of photons at three different energy levels, corresponding to the three different band gaps.  In particular, low-energy photons are captured that would pass through a conventional solar cell...more >>




  • An intermediate band solar cell using dilute GaNAs (~2% N) HMA demonstrates an optical activity of three energy bands that absorb and convert into electrical current the crucial part of the solar spectrum. 
  • The narrow intermediate band acts only as a “stepping stone” enabling efficient use of low energy solar photons


Highly Mismatched Alloys

Highly mismatched alloys (HMAs) is a new class of semiconductors formed through alloying of distinctly different materials. HMAs have  the electronic band structure drastically different from that of the component materials, offering unprecedented flexibility in controlling the band gap and the location of the conduction and valence band edges.





Ideal Transparent Conductor for Full Spectrum PV

Strong absorption and reflection by high concentration free carrier gas is responsible for low transparency of standard transparent conducting oxides (TCOs) in the infrared (IR) region (l>1000 nm) and restricts the applications of these materials to photovoltaics that do not utilize the IR part of the solar spectrum.  Maintaining low resistivity and low free carrier absorption requires TCOs with the highest possible charge carrier mobility.Recently we have developed high mobility CdO based transparent conducting oxides (TCOs) with exceptionally high conductivity (>104 S/cm) and transmission window in the wavelength range from 400 to >1500 nm making this material an ideal TCO for photovoltaics with low band gap absorbers.




News

  • InN work makes the top 50 list of APL Pionieering work on InN by our group, Appl. Phys. Lett. 80(21), 3967-9 (2002), makes the list of "Top 50 Most Cited Papers from 50 Years of Applied Physics ...
    Posted Apr 21, 2012, 5:34 PM by Kin Yu
  • New Nature Materials Paper on Spintronics Materials Work by Wladek Walukiewicz and Kin Man Yu on spintronics resolved a long-standing controversy regarding ferromagnetism in dilute magnetic semiconductors, February 2012. (news story)
    Posted Apr 21, 2012, 5:21 PM by Kin Yu
  • New patent granted U.S. Patent No. 8,039,740, "Single P-N junction tandem photovolatic device," by  Walukiewicz, Ager and Yu, has been issued, October 2011. (patent)
    Posted Apr 21, 2012, 5:20 PM by Kin Yu
  • Everything you always wanted to know about RBS (but were afraid to ask):  Kin Man Yu has made a nice website about his impressive new RBS machine. 
    Posted Feb 18, 2011, 12:32 PM by Lothar Reichertz
  • Engineering the Electronic Band Structure for Multiband Solar Cells Our group recently made it into the LBNL news, Physics Synopsis, Semiconductor Today, ScienceDaily and others. Click here for the original article.
    Posted Feb 23, 2011, 2:07 PM by Lothar Reichertz
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