According to the American Energy Information Administration (EIA), the global demand for energy is expected to grow 56 % by 2040. Nonetheless, 80 % of the world energy is expected to keep coming from fossil fuels. These are pollutant sources that not only increase an ongoing problematic global warming but are also often extracted from regions of high political instabilities. One possible candidate that can remedy this problem is the solar cell. These are semiconductor devices that use a nearly inexhaustible and green energy supply. Nevertheless, the detailed balance maximum efficiency for solar cells is limited to approximately 46 %.
In our group we have been investigating both theoretically [*1][*2] and experimentally[*3][*4] nanostructured materials that might be able to circumvent this limit with multiple carrier generation. Our main effort is on the preparation and characterization of oxide semiconductors by low-cost processes such as the low-temperature sol-gel chemistry.
In this seminar, the thermodynamics of P-N solar cells will be discussed and then some theoretical results from Monte Carlo simulations on gel structures will be shown. Our results suggest that there is a disorder threshold that separates fracton and phonon states. Moreover, the nanoparticles that compose the gel structure can be tuned to form either Zipf scale-free or Poisson networks depending on the synthesis temperature and concentration of precursors.
Experimentally, we have been synthesizing monolithic high-surface area tin oxide and tungsten trioxide aerogels by a sol-gel technique.[*3} A full characterization with SEM/TEM, BET/BJH, XRD, UV/Vis, FTIR, PL, PIXE and Thermogravimetry was performed. Our results indicate that the sol-gel synthesis inadvertently produces materials with oxygen deficiency. These defects produces a Burstein-Moss shift in oxide semiconductors, which is readily detectable by optical spectroscopy and severly changes its electrical properties.[*4]
Along this seminar all techniques will be thoroughly discussed and experimental results will be compared to theoretical models.
[*1] E. L. da Rocha and C. R. da Cunha, Chaos, Solitons & Fractals 44 (2011) 241.
[*2] R. V. Morales, C. R. da Cunha and C. R. Rambo, Physica A 406 (2014) 131.
[*3] C. R. da Cunha, G. H. Toffolo, C. E. I. dos Santos and R. P. Pezzi, J. Non-Cryst. Sol. 380 (2013) 48.
[*4] C. R. da Cunha, F. D. da Silva and R. Morales, MRS Proc. 1731 (2015).