Many methods to improve the solar cell’s efficiency beyond current generation of bulk and thin film of photovoltaic (PV) devices have been reported during the last five decades. Concepts such as multiple exciton generations (MEG), carrier multiplication (CM), hot carrier extraction, and intermediate band solar cells have fundamental flaws, and there is no experimental evidence of fabricating practical higher efficiency solar cells based on the proposed concepts. To take advantages of quantum features of nanostructures for higher performance PV devices, self-assembly-based bottom-up processing techniques are not suitable for manufacturing due to inherent problems of variability, defects, reliability, and yield. For processing nanostructures, new techniques need to be invented with the features of critical dimensional control, structural homogeneity, and lower cost of ownership as compared to the processing tools used in current generations of bulk and thin-film solar cells. 1. Introduction Starting with providing power to first communication satellite, Telstar, in 1962, photovoltaic (PV) systems have evolved to a market size of about 16 GW in 2010. Current commercial PV market is based on bulk solar cells (Si and III-V compound semiconductors) and thin-film solar cells based on a-Si, CdTe, and CuInGaSe2, while the devices are based on p-n homo- and heterojunctions and tandem junction solar cells. In case of III-V compound semiconductor-based concentration solar cells, one sun efficiency of 35.8% has been achieved [1]. Being an active area of research, new materials and structures are constantly being investigated in the hope of getting efficiencies higher than the typical bulk silicon solar cell efficiency of about 20%. Solar cells, which can be possibly made from engineered materials and nanostructures, are often called “third-generation PV cells” [2], with the materials themselves being referred to as “next generation materials,” “smart materials,” or “intelligent materials.” In reality, despite the semantics and the buzz, there has been no improvement in the efficiency of a solar cell using the so called “smart materials.” Of course, with better engineering, conventional bulk and thin-film solar cells have become more reliable, their cost has decreased over the years, and their efficiencies have also increased by a small percentage. However, this increase in efficiency cannot be attributed to any nanostructured smart material. This raises the interesting first question—during the last 10 years, why has there been no significant increase in the
References
[1]
T. Takamoto, T. Agui, A. Yoshida et al., “World's highest efficiency triple-junction solar cells fabricated by inverted layers transfer process,” in Proceedings of the 35th IEEE Photovoltaic Specialists Conference (PVSC '10), pp. 412–417, June 2010.
[2]
M. A. Green, “Third generation photovoltaics: ultra-high conversion efficiency at low cost,” Progress in Photovoltaics, vol. 9, no. 2, pp. 123–135, 2001.
[3]
C. Cui and D. Mattioli, “No silver lining left for users of the metal,” The Wall Street Journal, April 2011.
[4]
R. Singh and J. D. Leslie, “Economic requirements for new materials for solar photovoltaic cells,” Solar Energy, vol. 24, no. 6, pp. 589–592, 1980.
[5]
R. Singh, N. Gupta, G. F. Alapatt, R. Podila, and K. F. Poole, “Prospects of nanostructure-based solar cells for manufacturing future generations of photovoltaic modules,” International Journal of Photoenergy, vol. 2009, Article ID 154059, 13 pages, 2009.
[6]
R. Singh, “Why silicon is and will remain the dominant photovoltaic material,” Journal of Nanophotonics, vol. 3, Article ID 032503, 2009.
[7]
M. A. Green, K. Emery, Y. Hishikawa, W. Warta, and E. W. Dunlop, “Solar cell efficiency tables (version 38),” Progress in Photovoltaics, vol. 19, no. 1, pp. 565–572, 2011.
[8]
M. J?rgensen, K. Norrman, and F. C. Krebs, “Stability/degradation of polymer solar cells,” Solar Energy Materials and Solar Cells, vol. 92, no. 7, pp. 686–714, 2008.
[9]
K. Kawano, R. Pacios, D. Poplavskyy, J. Nelson, D. D. C. Bradley, and J. R. Durrant, “Degradation of organic solar cells due to air exposure,” Solar Energy Materials and Solar Cells, vol. 90, no. 20, pp. 3520–3530, 2006.
[10]
P. Buffat and J. P. Borel, “Size effect on the melting temperature of gold particles,” Physical Review A, vol. 13, no. 6, pp. 2287–2298, 1976.
[11]
R. Singh, P. Chandran, M. Grujicic, et al., “Dominance of silicon CMOS based semiconductor manufacturing beyond international technology roadmap and many more decades to come,” in Semiconductor Fabtech, pp. 104–113, 30th edition, 2006.
[12]
V. V. Pokropivny and V. V. Skorokhod, “Classification of nanostructures by dimensionality and concept of surface forms engineering in nanomaterial science,” Materials Science and Engineering C, vol. 27, no. 5–8, pp. 990–993, 2007.
[13]
J. Henk, Introduction to the Theory of Nanostructures, International Max Planck Research School on Science and Technology of Nanostructures, 2006.
[14]
W. Shockley and H. J. Queisser, “Detailed balance limit of efficiency of p-n junction solar cells,” Journal of Applied Physics, vol. 32, no. 3, pp. 510–519, 1961.
[15]
R. T. Ross and A. J. Nozik, “Efficiency of hot-carrier solar energy converters,” Journal of Applied Physics, vol. 53, no. 5, pp. 3813–3818, 1982.
[16]
A. Luque and A. Martí, “Increasing the efficiency of ideal solar cells by photon induced transitions at intermediate levels,” Physical Review Letters, vol. 78, no. 26, pp. 5014–5017, 1997.
[17]
A. J. Nozik, “Quantum dot solar cells,” Physica E, vol. 14, no. 1-2, pp. 115–120, 2002.
[18]
S. Kolodinski, J. H. Werner, T. Wittchen, and H. J. Queisser, “Quantum efficiencies exceeding unity due to impact ionization in silicon solar cells,” Applied Physics Letters, vol. 63, no. 17, pp. 2405–2407, 1993.
[19]
A. Shabaev, A. L. Efros, and A. J. Nozik, “Multiexciton generation by a single photon in nanocrystals,” Nano Letters, vol. 6, no. 12, pp. 2856–2863, 2006.
[20]
M. Wolf, “Limitations and possibilities for improvement of photovoltaic solar energy converters: part I: considerations for earth's surface operation,” Proceedings of the IRE, vol. 48, pp. 1246–1263, 1960.
[21]
A. J. Nozik, “Exciton multiplication and relaxation dynamics in quantum dots: applications to ultra-high efficiency solar photon conversion,” in Proceedings of the 4th IEEE World Conference on Photovoltaic Energy Conversion (WCPEC '06), pp. 40–44, May 2006.
[22]
V. I. Klimov, “Mechanisms for photogeneration and recombination of multiexcitons in semiconductor nanocrystals: implications for lasing and solar energy conversion,” Journal of Physical Chemistry B, vol. 110, no. 34, pp. 16827–16845, 2006.
[23]
C. M. Isborn, S. V. Kilina, X. Li, and O. V. Prezhdo, “Generation of multiple excitons in PbSe and CdSe quantum dots by direct photoexcitation: first-principles calculations on small PbSe and CdSe clusters,” Journal of Physical Chemistry C, vol. 112, no. 47, pp. 18291–18294, 2008.
[24]
P. V. Kamat, “Quantum dot solar cells. Semiconductor nanocrystals as light harvesters,” Journal of Physical Chemistry C, vol. 112, no. 48, pp. 18737–18753, 2008.
[25]
R. J. Ellingson, M. C. Beard, J. C. Johnson et al., “Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots,” Nano Letters, vol. 5, no. 5, pp. 865–871, 2005.
[26]
G. Konstantatos and E. H. Sargent, “Solution-processed quantum dot photodetectors,” Proceedings of the IEEE, vol. 97, no. 10, Article ID 5247124, pp. 1666–1683, 2009.
[27]
R. Merritt, “Intel details its first 22 nm processer,” , http://www.eetasia.com/ART_8800651608_499489_NT_066e1853.HTM.
[28]
S. Kundu and A. Sreedhar, Nanoscale CMOS VLSI Circuits: Design for Manufacturability, McGraw-Hill, New York, NY, USA, 2010.
[29]
S. Y. Chou, P. R. Krauss, W. Zhang, L. Guo, and L. Zhuang, “Sub-10 nm imprint lithography and applications,” Journal of Vacuum Science and Technology B, vol. 15, no. 6, pp. 2897–2904, 1997.
[30]
D. Clark and S. Tibken, “Intel finds chip-design flaw,” The Wall Street Journal, February 2011.
[31]
M. T. Heemels, R. Dhand, and L. Allen, “Foreword: apoptosis,” Nature, vol. 407, pp. 767–770, 2000.
[32]
O. Loh, X. Wei, C. Ke, J. Sullivan, and H. D. Espinosa, “Robust carbon-nanotube-based nano-electromechanical devices: understanding and eliminating prevalent failure modes using alternative electrode materials,” Small, vol. 7, no. 1, pp. 79–86, 2011.
[33]
R. Singh, T. Boland, and R. Mulye, “Prospects of incorporating directed self assembly into semiconductor manufacturing,” in Semiconductor Fabtech, vol. 36, pp. 67–72, 36th edition, 2007.
[34]
J. J. Coleman, J. D. Young, and A. Garg, “Semiconductor quantum dot lasers: a tutorial,” Journal of Lightwave Technology, vol. 29, no. 4, pp. 499–510, 2011.
[35]
S. H. Baek, H. S. Jang, and J. H. Kim, “Characterization of optical absorption and photovoltaic properties of silicon wire solar cells with different aspect ratio,” Current Applied Physics, vol. 11, pp. S30–S33, 2010.
[36]
G. Nair, L.-Y. Chang, S. M. Geyer, and M. G. Bawendi, “Perspective on the prospects of a carrier multiplication nanocrystal solar cell,” Nano Letters, vol. 11, no. 5, pp. 2145–2151, 2011.
[37]
M. Horiguchi and K. Itoh, “Redundancy,” in Nanoscale Memory Repair, pp. 19–67, Springer, New York, NY, USA, 2011.
[38]
N. López, L. A. Reichertz, K. M. Yu, K. Campman, and W. Walukiewicz, “Engineering the electronic band structure for multiband solar cells,” Physical Review Letters, vol. 106, no. 2, Article ID 028701, 4 pages, 2011.
[39]
J. Tang, K. W. Kemp, S. Hoogland et al., “Colloidal-quantum-dot photovoltaics using atomic-ligand passivation,” Nature Materials, vol. 10, no. 10, pp. 765–771, 2011.
[40]
E. C. Cho, S. Park, X. Hao et al., “Silicon quantum dot/crystalline silicon solar cells,” Nanotechnology, vol. 19, no. 24, Article ID 245201, 2008.
[41]
J. J. Choi, Y. F. Lim, M. B. Santiago-Berrios et al., “PbSe nanocrystal excitonic solar cells,” Nano Letters, vol. 9, no. 11, pp. 3749–3755, 2009.
[42]
N. Zhao, T. P. Osedach, L. Y. Chang et al., “Colloidal PbS quantum dot solar cells with high fill factor,” ACS Nano, vol. 4, no. 7, pp. 3743–3752, 2010.
[43]
A. Ebong, I. B. Cooper, B. Rounsaville et al., “High efficiency inline diffused emitter (ILDE) solar cells on mono-crystalline CZ silicon,” Progress in Photovoltaics, vol. 18, no. 8, pp. 590–595, 2010.
[44]
J. W. Eaton, GNU Octave Manual, Network Theory Limited, 2002.
[45]
W. F. van Dorp, I. Lazi?, A. Beyer et al., “Ultrahigh resolution focused electron beam induced processing: the effect of substrate thickness,” Nanotechnology, vol. 22, no. 11, Article ID 115303, 2011.
[46]
P. McGuire and A. Mullins, “Key aspects of advanced process control,” Future Fab International, vol. 4, no. 1, 1998.
[47]
V. Giovannetti, S. Lloyd, and L. MacCone, “Advances in quantum metrology,” Nature Photonics, vol. 5, no. 4, pp. 222–229, 2011.
[48]
R. Singh, Sustainable Energy for Sustainable Economic Growth, Forthcoming Book, 2012.
[49]
M. C. Beard, K. P. Knutsen, P. Yu et al., “Multiple exciton generation in colloidal silicon nanocrystals,” Nano Letters, vol. 7, no. 8, pp. 2506–2512, 2007.
[50]
K. Bullis, “Nanocrystals for Superefficient Solar Cells,” Technology Review, March 2007, http://www.technologyreview.com/energy/19256.