W. Li, Y. Wang, H. Lin, S. Ismat Shah, C. P. Huang, D. J. Doren, Sergey A. Rykov, J. G. Chen, and M. A. Barteau, Band gap tailoring of Nd3-doped TiO2 nanoparticles, Appl. Phys. Lett. 83, 4143 (2003). Robert W. Birkmire, Evolution and future prospects of inorganic photovoltaics, Proc. SPIE 5520, 9 (2004). Amita Goyal, Abdul K. Rumaiz, and Y. Miao, Sukti Hazra, C. Ni, and S. Ismat Shah, Synthesis and characterization of TiO2–Ge nanocomposites, J. Vac. Sci. Technol. B 26, 1315 (2008).
The depleting reserves of conventional energy resources have created an increasing need for the development of alternative form of energy in the past few decades. Particularly, energy from Sun is expected to be a great contender, in the form of photovoltaics cells and photochemical cells, since it is the only long-term renewable energy provider. Research in this area has led to develop a huge spectrum of solar cells, which are commonly classified as:
- first generation solar cell comprised mostly of silicon wafers
- second generation solar cells utilizing thin film technology
- third generation solar cells aiming to achieve photovoltaic with efficiencies as high as 80% - these include tandem cells, hot carrier solar cells, solar cells producing multiple electron-hole pair per photon through impact ionization, multiband and impurity solar cells and thermophotovoltaic, and thermophotonic solar cells.
At present, highest conversion efficiency of single junction solar cells, which include the presently available silicon solar cells and thin film solar cells, is 33%, while the record kept by multijunction cells is 41%.
- Nanocomposites based on titania hold promise but TiO2 has a unsuitably wide band gap (~3.2 eV) which requires that either the material has to be sensitized, preferably by a solid sensitizer like Ge, or its band gap has to be tailored by doping or size manipulation. Our current research spread over both of these approaches.
- Another material that has recently been attracting much attention is CuInGaSe2 (CIGS). With an absorption coefficient that is about 100 times higher than that of Si, CIGS allows the possibility of using a very thin film for device fabrication on flexible substrates. By changing the chemistry of the films, the band gap can also be tuned for increased conversion efficiency. A non-vacuum synthesis process will increase the commercial attraction. We are developing solvothermal processes for a single step synthesis of CIGS particles and non-vacuum processes for the fabrication of devices based on these particles.
- Growth and characterization of thin film semiconductors and devices for photovoltaic applications, emphasizing the inter-relationship between the growth process, film structural and electro-optical properties and device performance.
Campus-wide Interdisciplinary Collaboration:
- Robert W. Birkmire (Director of the Institute of Energy Conversion)