三五族多接面串聯式太陽能電池(III-V-base tandem solarcell)是由不同材料逐層堆疊所組成的化合物半導體結構，每一接面材料對應不同的能隙(energy band-gap)分佈，可分別吸收太陽光譜中不同波段以提高元件之光電功率轉換效率。在設計一高功率轉換效率之多接面串聯式太陽能電池時，有一項重要的物理因素值得探討，即在各個接面電池間，其光致電流(photon-generated current)是否有達到電流匹配(current matching)之議題。根據基本電學原理，一串聯電路中其導通電流須為一致。因此，對一多接面串聯式太陽能電池而言，其各個接面電池在照光後產生不同光致電流時，將以最小電流作為整個元件之輸出電流。換言之，整體太陽能電池最終輸出光電流會被產生最小電流的該層接面電池所限制。本論文主要研究使用硒化鎘(cadmium selenide, CdSe)量子點(quantum dots, QDs)來增強磷化銦鎵/砷化鎵/鍺 (InGaP/GaAs/Ge)三接面串聯式太陽能電池之光電功率轉換效率。量子點具有獨特的量子侷限效應(quantum confinement effect)，可以用來調變太陽光譜，以利於多接面串聯式太陽能電池整體轉換效率的提升。我們發現，其所增加之光電功率轉換效率與元件本身的結構，以及量子點的尺寸有很大的關連。我們進一步建立一套物理模型來設計與優化量子點尺寸，以達到最佳之元件功率轉換效率輸出。最後，本論文在磷化銦鎵/砷化鎵/鍺串聯太陽能電池上旋轉塗佈(spin coating)濃度7 mg/mL、直徑為4.2nm的硒化鎘量子點，相較於未塗佈量子點的裸片太陽能電池，光電功率轉換效率大幅且穩定地增加了10.39%。由於合成與旋轉塗布CdSe量子點是低成本且成熟的製程技術，並可直接融於現行太陽能元件的製造流程；因此我們相信，本論文所提出之新穎結構將可廣泛應用於下世代高效率之相關能源光電元件。

A III-V multi-junction tandem solar cell is the most efficient photovoltaic structure that offers an extremely high power conversion efficiency. Current mismatching between each subcell of the device, however, is a significant challenge that causes the experimental value of the power conversion efficiency to deviate from the theoretical value. In this work, we explore a promising strategy using CdSe quantum dots (QDs) to enhance the photocurrent of the limited subcell to match with those of the other subcells and to enhance the power conversion efficiency of InGaP/GaAs/Ge tandem solar cells. The underlying mechanism of the enhancement can be attributed to the QD’s unique capacity for photon conversion that tailors the incident spectrum of solar light; the enhanced efficiency of the device is therefore strongly dependent on the QD’s dimensions. As a result, by appropriately selecting and spreading 7 mg/mL of CdSe QDs with diameters of 4.2 nm upon the InGaP/GaAs/Ge solar cell, the power conversion efficiency shows an enhancement of 10.39% compared to the cell’s counterpart without integrating CdSe QDs.

[1] Exergy (available energy) Flow Charts 2.7 YJ solar energy each year for two billion years vs. 1.4 YJ non-renewable resources available once.
[2] Y. -C. Yao, M. -T. Tsai, H. -C. Hsu, L. -W. She, C. -M. Cheng, Y. -C. Chen, C. -J. Wu, and Y. -J. Lee, “Use of two-dimensional nanorod arrays with slanted ITO film to enhance optical absorption for photovoltaic applications,” Opt. Express 20(4), 3479-3489 (2012).
[3] Y. -J. Lee, M. -H. Lee, C. -M. Cheng, and C. -H. Yang, “Enhanced conversion efficiency of InGaN multiple quantum well solar cells grown on patterned sapphire substrates,” Appl. Phys. Lett. 98(26), 263504 (2011).
[4] X. Yan, D. J. Poxson, J. Cho, R. E. Welser, A. K. Sood, J. K. Kim, and E. F. Schubert, “Enhanced omnidirectional photovoltaic performance of solar cells by multiple-discrete-layer tailored- and low- refractive-index anti-reflection coatings,” Adv. Funct. Mater. 23(5), 583-590 (2013).
[5] J. K. Sheu, C. C. Yang, S. J. Tu, K. H. Chang, M. L. Lee, W. -C. Lai, and L. -C. Peng, “Demonstration of GaN-based solar cells with GaN/InGaN superlattice absorption layers,” IEEE Electron Device Lett. 30(3), 225–227 (2009).
[6] M. C. Wei, S. J. Chang, C. Y. Tsia, C. H. Liu, and S. C. Chen, “ SiNx deposited by in-line PECVD for multi-crystalline silicon solar cells,” SOL ENERG MAT SOL C., 80(2), 215-219 (2006).
[7] A. G. Bhuiyan, K. Sugita, A. Hashimoto, and A. Yamamoto, “ InGaN Solar Cells: Present State of the Art and Important Challenges,” Photovoltaics, IEEE Journal of 2(3), 276-293 (2012).
[8] R. R. King, D. C. Law, K. M. Edmondson, C. M. Fetzer, G. S. Kinsey, H. Yoon, R. A. Sherif, and N. H. Karam, “40% efficient metamorphic GaInP/GaInAs/Ge multijunction solar cells,” Appl. Phys. Lett. 90(18), 183516 (2007).
[9] S. W. Boettcher, J. M. Spurgeon, M. C. Putnam, E. L. Warren, D. B. Turner-Evans, M. D. Kelzenberg, J. R. Maiolo, H. A. Atwater, and N. S. Lewis, “Energy-conversion properties of vapor-liquid-solid–grown silicon wire-array photocathodes,” Science 327(5962), 185-187 (2010).
[10] J. Wallentin, N. Anttu, D. Asoli, M. Huffman, I. Åberg, M. H. Magnusson, G. Siefer, P. Fuss-Kailuweit, F. Dimroth, B. Witzigmann, H. Q. Xu, L. Samuelson, K. Deppert, and M. T. Borgström, “InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit,” Science 339(6123), 1057-1060 (2013).
[11] F. Hetsch, X. Xu, H. Wang, S. V. Kershaw, and A. L. Rohach, “Semiconductor nanocrystal quantum dots as solar cell components and photosensitizers: material, charge transfer, and separation aspects of some device toplogies,” J. Phys. Chem. Lett. 2, 1879–1887 (2011).
[12] M. S. Leite, R. L. Woo, J. N. Munday, W. D. Hong, S. Mesropian, D. C. Law, and H. A. Atwater, “Towards an optimized all lattice-matched InAlAs/InGaAsP/InGaAs multijunction solar cell with efficiency >50%,” Appl. Phys. Lett. 102(3), 033901 (2013).
[13] “Sharp Develops Concentrator Solar Cell with World's Highest Conversion Efficiency of 44.4%,” http://sharp-world.com/corporate/news/130614.html (2013)
[14] J. Geisz, D. Friedman, J. Ward, A. Duda, W. Olavarria, T. Moriarty, J. Kiehl, M. Romero, A. Norman, K. Jones, “40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions,” Appl. Phys. Lett. 93(12), 123505 (2008).
[15] Katsuaki Tanabe, “A review of ultrahigh efficiency III-V semiconductor compound solar cells: multijunction tandem, lower dimensional, photonic up/down conversion and plasmonic nanometallic structures,” Energies 2(3), 504–530 (2009).
[16] L. A. Kosyachenko, Solar Cells-Silicon Wafer-Based Technologies (InTech, Rijeka, Croatia, 2011), p. 335-337.
[17] W. Shockley and H. J. Queisser, “Detailed balance limit of efficiency of p-n junction solar cells,” J. Appl. Phys. 32(3), 510 (1961).
[18] M. W. Wanlass, S. P. Ahrenkiel, R. K. Ahrenkiel, D. S. Albin, J. J. Carapella, A. Duda, J. F. Geisz, S. Kurtz, T. Moriarty, R. J. Wehrer, and B. Wernsman, “Lattice-mismatched approaches for high-performance, III-V photovoltaic energy converters,” in Proceedings of the 31th IEEE Photovoltaic Specialists Conference (Institute of Electrical and Electronics Engineers, New York, 2005), pp. 530–535.
[19] R. R. King, M. Haddad, T. Isshiki, P. Colter, J. Ermer, H. Yoon, D. E. Joslin, and N. H. Karam, “Next-generation, high-efficiency III-V multijunction solar cells,” in Proceedings of the 28th IEEE Photovoltaic Specialists Conference (Institute of Electrical and Electronics Engineers, New York, 2000), pp. 998–1001.
[20] F. Dimroth, U. Schubert, and A. W. Bett, “25.5% efficient Ga0.35In0.65P/Ga0.83In0.17 as tandem solar cells grown on GaAs substrates,” IEEE Electron Dev. 21(5), 209–211 (2000).
[21] A. J. Nozik, “Quantum dot solar cells,” Physica E 14(1-2), 115–120 (2002).
[22] R. D. Schaller and V. I. Klimov, “High efficiency carrier multiplication in PbSe nanocrystals: Implications for solar energy conversion,” Phys. Rev. Lett. 92(18), 186601 (2004).
[23] A. Franceschetti, J. M. An, and A. Zunger, “Impact ionization can explain carrier multiplication in PbSe quantum dots,” Nano Lett. 6(10), 2191–2195 (2006).
[24] http://en.wikipedia.org/wiki/Impact_ionization
[25] M. Wolf, R. Brendel, J. H. Werner, and H. J. Queisser, “Solar cell efficiency and carrier multiplication in Si1-xGex alloys,” J. Appl. Phys. 83(8), 4213–4221(1998).
[26] C. -Y. Huang, D. -Y. Wang, C. -H. Wang, Y. -T. Chen, Y. -T. Wang, Y. -T. Jiang, Y. -J. Yang, C. -C. Chen, and Y. -F. Chen, “Efficient light harvesting by photon downconversion and light trapping in hybrid ZnS nanoparticles/Si nanotips solar cells,” ACS Nano 4(10), 5849–5854 (2010).
[27] Hertz, Heinrich. Ueber den Einfluss des ultravioletten Lichtes auf die electrische Entladung. Annalen der Physik. 1887, 267 (8): S. 983–1000. Bibcode:1887AnP...267..983H. doi:10.1002/andp.18872670827.(On an effect of ultra-violet light upon the electric discharge)
[28] The Nobel Prize in Physics 1921. Nobel Foundation.
[29] http://www.solarbuildingtech.com/Solar_PV_Tech/solar_photovoltaic_technologies.htm
[30] Third Generation Photovoltaics, M.A. Green, ISBN 978-3-540-26562-7(Print)ISBN 978-3-540-26563-4 (Online).
[31]http://www.daviddarling.info/encyclopedia/S/AE_small_solar_electric_systems_grid-connected.html
[32] Brus, L.E. (2007). "Chemistry and Physics of Semiconductor Nanocrystals". Retrieved 7 July 2009.
[33] Jump up ^ Norris, D.J. (1995). "Measurement and Assignment of the Size-Dependent Optical Spectrum in Cadmium Selenide (CdSe) Quantum Dots, PhD thesis, MIT". hdl:1721.1/11129.
[34] Jump up ^ Murray, C. B.; Kagan, C. R.; Bawendi, M. G. (2000). "Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies". Annual Review of Materials Research 30 (1): 545–610. Bibcode:2000AnRMS..30..545M. doi:10.1146/annurev.matsci.30.1.545.
[35] Reed MA, Randall JN, Aggarwal RJ, Matyi RJ, Moore TM, Wetsel AE (1988)."Observation of discrete electronic states in a zero-dimensional semiconductor nanostructure". PhysRevLett 60 (6): 535–537. Bibcode:1988PhRvL..60..535R.doi:10.1103/PhysRevLett.60.535. PMID 10038575.
[36] SIGMA-ALDRICH official web: http://www.sigmaaldrich.com/materials-science/nanomaterials/quantum-dots.html#ref
[37] Patrícia Maria Simões Martins, “ANÁLISE DE MERCADO DE EQUIPAMENTOS CIENTÍFICOS NA ÁREA BIOMÉDICA” Mestrado Integrado em Engenharia Biomédica Coimbra, Setembro 2009
[38]http://www.technologyreview.com/news/509801/quantum-dots-get-commercial-debut-in-more-colorful-sony-tvs/
[39] "Nanotechnology Information Center: Properties, Applications, Research, and Safety Guidelines". American Elements.
[40] Kastner, M. A. Physics Today, 1993, 46(1), 24.
[41] Ashoori, R. C. Nature, 1996, 379(6564), 413.
[42] Collier, C. P.; Vossmeyer, T.; Heath, J. R. Annual Review of Physical Chemistry, 1998, 49, 371. - See more at: http://www.sigmaaldrich.com/materials-science/nanomaterials/quantum-dots.html#ref
[43] Reimann, S. M.; Manninen, M. Reviews of Modern Physics, 2002, 74(4), 1283. - See more at: http://www.sigmaaldrich.com/materials-science/nanomaterials/quantum-dots.html#ref
[44] Bawendi, M. C.; Steigerwald, M. L.; Brus, L. E. Annual Review of Physical Chemistry, 1990, 41, 477. - See more at: http://www.sigmaaldrich.com/materials-science/nanomaterials/quantum-dots.html#ref
[45] Y. -J. Lee, C. -J. Lee, and C. -M. Cheng, “Enhancing the conversion efficiency of red emission by spin-coating CdSe quantum dots on the green nanorod light-emitting diode,” Opt. Express 18(104), A554-A561 (2010).
[46] D. Souri and K. Shomalian, “Band gap determination by absorption spectrum fitting method (ASF) and structural properties of different compositions of (60−x) V2O5–40TeO2–xSb2O3 glasses,” J. Non-Cryst. Solids 355(31-33), 1597–1601 (2009).
[47] ASTMG173–03, Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37 degree Tilted Surface (ASTM International, West Conshohocken, Pennsylvania, 2005).
[48] S.O. Kasap “Optoelectronics and Photonics Principles and Practices” p244.
[49] P. Bermel, C. Luo, L. Zeng, L. C. Kimerling, and J. D. Joannopoulos, “Improving thin-film crystalline silicon solar cell efficiencies with photonic crystals,” Opt. Express 15(20), 16986–17000 (2007).