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research:absorbers [2011/07/11 23:02]
research:absorbers [2013/06/22 20:16] (current)
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 +====== Non-conventional Solar Absorbers ======
 +Low cost, earth-abundant light absorbers are of great interest for use in terrestrial photovoltaics and in artificial photosynthesis. ​ Non-conventional solar absorbers, e.g., zinc phosphide (Zn<​sub>​3</​sub>​P<​sub>​2</​sub>​),​ cuprous oxide (Cu<​sub>​2</​sub>​O) and pyrite (FeS<​sub>​2</​sub>​),​ are promising materials for solar energy conversion and have received renewed interests after early work in 1980s. ​ The Lewis group is interested in studying the interface chemistry and fundamental energy-conversion properties of these non-conventional solar absorbers.
 +====== Zinc Phosphide ======
 +Zinc phosphide is one of the most promising materials for low-cost solar cells. ​ It has a direct bandgap near 1.5 eV, both of its constituent elements are cheap and earth abundant and electron diffusion length in p-type Zn<​sub>​3</​sub>​P<​sub>​2</​sub>​ is relatively long (>10 um).
 +We have successfully demonstrated synthesis of quasi-single crystal Zn<​sub>​3</​sub>​P<​sub>​2</​sub>​ by physical vapor transport (Figure 1).  We are investigating various surface treatment for  Zn<​sub>​3</​sub>​P<​sub>​2</​sub>​ to decrease the surface recombination velocity (Figure 2).  We are also investigating solar cell performances of Mg/​Zn<​sub>​3</​sub>​P<​sub>​2</​sub>​ diodes.\\
 +//Fig. 1. Preparation of quasi-single crystal Zn<​sub>​3</​sub>​P<​sub>​2</​sub>​ substrates.//​\\
 +//Fig. 2. Photoluminescence (PL) data demonstrate the improved quality of chemically-treated Zn<​sub>​3</​sub>​P<​sub>​2</​sub>​ surfaces. ​  ​Time-resolved PL decays show a reduction in surface recombination velocity (SRV) and inset shows enhanced steady-state PL from HF:​H<​sub>​2</​sub>​O<​sub>​2</​sub>​ treatment.//​\\  ​
 +====== Cuprous Oxide  ======
 +Cuprous oxide is a native p-type semiconductor,​ with a bandgap of 2.0 eV and relatively high absorption coefficient in the visible spectrum range. ​  
 +We are developing synthesis techniques for preparing high quality Cu<​sub>​2</​sub>​O substrates (Figure 3).  We are using semiconductor/​liquid contacts to investigate the energy-conversion properties of prepared substrates (Figure 4).  We are also interested in exploring other hetero-junction partners for cuprous oxide substrates.\\
 +//Fig. 3. Synthesis of Cu<​sub>​2</​sub>​O substrates by high temperature thermal oxidation.//​
 +//Fig. 4. 820 mV open-circuit voltages were observed from Cu<​sub>​2</​sub>​O photoelectrodes in contact with the decamethylcobaltocene<​sup>​+/​0</​sup>​ (Me<​sub>​10</​sub>​CoCp<​sub>​2</​sub><​sup>​+/​0</​sup>​) redox couple. ​ Inset shows an electron diffraction image of the grain structure in Cu<​sub>​2</​sub>​O substrates.//​\\
 +====== References ​ ======
 +  - G. M. Kimball, A. M. Muller, N. S. Lewis and H. A. Atwater, "​Photoluminescence-based measurements of the energy gap and diffusion length of Zn<​sub>​3</​sub>​P<​sub>​2</​sub>",//​Appl. Phys. Lett. 95, 112103 (2009).// ​
 +  - C. Xiang, G. M. Kimball, R. L. Grimm, B. S. Brunschwig, H. A. Atwater, and N. S. Lewis, "820 mV open-circuit voltages from Cu<​sub>​2</​sub>​O/​CH<​sub>​3</​sub>​CN junctions",​ //Energy Environ. Sci.,4, 1311-1318 (2011).//
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Lewis Research Group, Division of Chemistry and Chemical Engineering
Caltech 127-72, 1200 East California Boulevard, Pasadena, California 91125