In this thesis, we have proposed and validated several novel structures for achieving high efficiency solar cells. Our scientific achievement is summarized as follows.
First, we have successfully demonstrated that 2D Si-nanorod arrays with slanted ITO films have strong and angle-insensitive optical absorption over a broad range of incident wavelengths, and that they are advantageous for photovoltaic applications.
Additionally, the results concerning the optical properties of 2D nanorod arrays and slanted ITO films are not limited to Si-based solar cell, and the revealed geometry is ready to apply on other kinds of material systems with nanoscale features. In terms of the device’s result, the slanted ITO film integrating with metal-induced chemical-etching SiNW arrays shows an efficiency up to about 0.26%, much lower than that of standard bulk Si solar cell. Ongoing research in the future to enhance the efficiency of the device is focused on decreasing series resistance and increasing shunt resistance by appropriately aligning doped polarity of contact materials, and by diminishing the interfacial recombination of photocarriers via surface passivation.
Additionally, instead of fabricating the SiNW arrays on the bulk Si substrate, the achievement of SiNW arrays on the thin-film geometry not only provides a high tolerance for material quality demand; and further, it can also avoid the undesired loss in power conversion efficiency of solar cells as the larger series resistance will be produced in the bulk Si and its diffusion region compared with that in thin-film geometry.
Second, we propose a new type of III-nitride n-i-p solar cell not formed by impurity doping, but by the polarization-induced doping. The approach of polarization-induced doping is particularly useful for III-nitride solar cells with high
indium contents in the InxGa1-xN absorption layer as the band discontinuity at hetero-interfaces is considerably alleviated. Most importantly, as polarization charges are atomic in origin and do not need thermal energy to be activated, the short-circuit current of the proposed polarization-induced doping n-i-p solar cell are essentially independent of temperature and contribute to a high power conversion efficiency, and that offers a great potential for the next generation of photovoltaic cells. Our proposed structure has to be further examined by MOCVD growth to explore the fabrication limitations of real solar devices, and to validate the calculations for practical applications.
Finally, we have demonstrated the use of CdSe QDs to tailor the incident spectrum of solar light and achieve efficient solar spectrum utilization in InGaP/GaAs/Ge tandem solar cells. We have also shown that the integration of CdSe QDs can significantly enhance the power conversion efficiency of an InGaP/GaAs/Ge tandem solar cell under AM1.5 illumination by both theory and experiment. In terms of the eco-friendly concerns, the CdSe QDs used in this thesis shall be replaced by both non-toxic and cost-effective QDs composed of different material systems such as Dysprosium Doped Yttrium Vanadate Colloid (PhosphorDotsTM) or ZnS-AgInS2 (ZAIS) QDs [6.1].
Additionally, the stability of QDs is the most important issue has to be considered.
After that, we believe that the proposed scheme is viable and highly promising for future generations of energy devices.
--- Reference
[6.1] P. Subramaniam, S. J. Lee, S. Shah, S. Patel, V. Starovoytov, and K.-B. Lee,
“Generation of a library of non-toxic quantum dots for cellular imaging and siRNA delivery,” Adv. Mater., 24(29), 4014–4019 (2012).
Appendix A: Derivation of the Reflectance and Transmittance of the Fabry–Pérot Etalon
Figure 1 The schematic illustration of Fabry–Pérot etalon undergoing multiple internal reflections.
The Fabry–Pérot interferometer (FPI) or Fabry–Pérot etalon (FPE), named after its inventors can be considered as the simplest type of optical resonator. As shown in Fig. 1, such an instrument consists of two parallel dielectric mirrors separated at a distance d and its refractive index is n2. Here we assume that medium front of the FPE is given the refractive index of n1 and the back one is given of n3. Taking the etalon as the absorber material into consideration, of which complex refraction index
n
2 is given by the relationshipn
2= n
2- i
2. Medium 1(n1) and medium 2(n2) form the plane of incidence.A normal is perpendicular to the plane of incidence. Assuming incident angle between the oblique incidence and the normal is
1. According to Snell's law, the following refractive angles in medium 2 and medium 3 are 2 and 3, respectively. The derivation of the reflectance R and transmittance T undergoing multiple internal reflections in Fabry–Pérot etalon is derived as follows,2
2
2 2 2
2
2 2 2
(1) The propagation phase term of 1D wavefunction in the 2nd layer is given by
[ ]
( ) [ ( )],
2
where complex refractive index: , complex wave number: cos 2
attenuation coefficient: 2 Im( ) 4 cos ,
' : sin sin sin for ,
(3) The reflection coefficient and transmission coeffici
n n
The extensions of angular-dependent reflectance R(,
) and transmittance T(, ) of
If we allow for the existence of losses in the etalon medium (n2), its absorption A can be determined once the theoretical reflectance R and transmittance T experiencing multiple reflections and transmissions in the etalon were obtained from above derivation. In general, R, T, and A are as a function of the incident angle and wavelengths and the total amounts of these quantities are consistent with conservation of probability. Their relationship can be expressed as follows A(,)+R(,)+T(,) =1.
Appendix B: Publications, Awards & Honors
Journal Paper
[1] Meng-Tsan Tsai, Meng-Tsan Tsai, Feng-Yu Chang, Yung-Chi Yao(姚詠祺), Jie Mei, and Ya-Ju Lee*, “Optical inspection of solar cells using phase-sensitive optical coherence tomography,” Solar Energy Materials and Solar Cells, Accepted, 2015. (IF: 5.030; Ranking: 16/136=11.76% in PHYSICS, APPLIED) [2] Ya-Ju Lee*, Yung-Chi Yao(姚詠祺), and Zu-Po Yang, “Numerical analysis on
polarization-induced doping III-nitride n-i-p solar cells,” IEEE Photonics Journal, Accepted, 2015. (IF: 2.33; Ranking : 45/248=18.1% in Engineering, Electrical &
Electronics)
[3] Meng-Tsan Tsai, Zu-Po Yang, Ting-Shiuan Jing, Hsin-Hwa Hsieh, Yung-Chi Yao(姚詠祺), Tai-Yuan Lin, Yang-Fang Chen, and Ya-Ju Lee*, “Achieving graded refractive index by use of ZnO nanorods/TiO2 layer to enhance omnidirectional photovoltaic performances of InGaP/GaAs/Ge triple-junction solar cells,” Solar Energy Materials and Solar Cells, Accepted, 2015. (IF: 5.030; Ranking:
16/136=11.76% in PHYSICS, APPLIED)
[4] Yung-Chi Yao( 姚 詠 祺 ), Chun-Ying Huang, Tai-Yuan Lin, Li-Lien Cheng, Ching-Yun Liu, Mei-Tan Wang, Jung-Min Hwang, and Ya-Ju Lee*, “Manipulation of polarization effect to engineer III-nitride HEMTs for normally-off operation,”
Microelectronic Engineering, Vol 138, no.20, pp. 1-6, 2015. (IF: 1.338; Ranking:
110/248=44.35% in ENGINEERING, ELECTRICAL & ELECTRONIC)
[5] Ya-Ju Lee*, Zu-Po Yang, Pin-Guang Chen, Yung-An Hsieh, Yung-Chi Yao(姚詠 祺), Ming-Han Liao, Min-Hung Lee, Mei-Tan Wang, and Jung-Min Hwang,
“Monolithic integration of GaN-based light-emitting diodes and metal-oxide-semiconductor field-effect transistors,” Optics Express, Vol. 22, Issue S6, pp. A1589-A1595, 2014. (IF: 3.546; Ranking: 4/79=5% in Optics)
[6] Ya-Ju Lee*, Yung-Chi Yao(姚詠祺), Chun-Ying Huang, Tai-Yuan Lin, Li-Lien Cheng, Ching-Yun Liu, Mei-Tan Wang, and Jung-Min HWang, “High Breakdown Voltage in AlGaN/GaN HEMTs using AlGaN/GaN/AlGaN Quantum-Well Electron-Blocking-Layers,” Nanoscale Research Letters, Vol. 9, No. 433, pp. 1-9,
2014. (IF: 2.481; Ranking: 53/251=21.11% in MATERIALS SCIENCE, MULTIDISCIPLINARY)
[7] Chun-Ying Huang, Yung-Chi Yao(姚詠祺), Ya-Ju Lee*, Tai-Yuan Lin, Wen-Jang Kao, Jih Hwang, and Ying-Jay Yang, “Local nanotip arrays sculptured by atomic force microscope to enhance the light-output efficiency of GaN-based light-emitting diode structures,” Nanotechnology, Vol. 25, No. 19, 195401 (7pp), 2014. (IF: 3.842; Ranking: 18/128=14.1% in Physics, Applied; 34/241=14.1% in Materials Science, Multidisciplinary)
[8] Yung-Chi Yao(姚詠祺), Meng-Tsan Tsai, Chun-Ying Huang, Tai-Yuan Lin, Jinn Kong Sheu, and Ya-Ju Lee*, “Efficient collection of photogenerated carriers by Inserting double tunnel junctions in III-nitride p-i-n solar cells,” Appl. Phys. Lett., Vol. 103, No. 19, pp. 193503-1—193503-5, 2013. (IF: 3.794; Ranking:
20/128=15.6% in Physics, Applied)
[9] Ya-Ju Lee*, Yung-Chi Yao(姚詠祺), Meng-Tsan Tsai, An-Fan Liu, Min-De Yang, and Jiun-Tsuen Lai, “Current matching using CdSe quantum dots to enhance the power conversion efficiency of InGaP/GaAs/Ge tandem solar cells,” Optics Express, Vol. 21, No. S6, pp. A953-A963, 2013. (IF: 3.546; Ranking: 4/79=5% in Optics)
[10] Ya-Ju Lee*, Yung-Chi Yao(姚詠祺), and Chia-Hao Yang, “Directly electrical contact of slanted ITO film on axial p-n junction silicon nanowire solar cells,”
Optics Express, Vol. 21, No. S1, pp. A7-A14, 2013. (IF: 3.587; Ranking: 5/77=6%
in Optics)
[11] Yung-Chi Yao( 姚 詠 祺 ), Meng-Tsan Tsai, Hsu-Cheng Hsu, Li-Wei She, Chun-Mao Cheng, Yi-Ching Chen, Chien-Jang Wu, and Ya-Ju Lee*, “Use of two-dimensional nanorod arrays with slanted ITO film to enhance optical absorption for photovoltaic applications,” Optics Express, Vol. 20, No. 4, 3479-3489, 2012. (IF: 3.587; Ranking: 5/77=6% in Optics)
[12] Y.-C. Yao(姚詠祺), M.-T. Tsai, P.-W Lu, C.-J. Wu and Ya-Ju Lee*, “Effect of nanostructured architecture on the enhanced optical absorption in silicon thin-film solar cells,” Journal of Electromagnetic Waves and Applications , Vol.
26, No. 13, pp. 1798-1807, 2012. (IF: 2.965; Ranking: 18/244=7.3% in Engineering, Electrical & Electronic)
[13] Meng-Tsan Tsai, Ya-Ju Lee, Yung-Chi Yao(姚詠祺), Che-Yen Kung, Feng-Yu Chang, and Jiann-Der Lee, “Quantitative phase imaging with swept-source optical coherence tomography for optical measurement of nanostructures,” IEEE Ph otonics Technol ogy L etters , Vol. 24, No. 8, 640 - 642, 2012. (IF: 2.191;
Ranking: 42/244=17% in Engineering, Electrical & Electronic)
[14] Y.-C. Yao(姚詠祺), Y.-C. Chen, Ya-Ju Lee*, “Suppression of efficiency-droop effect of InGaN-based LEDs by using localized high indium quantum wells,” Proc.
of SPIE, Vol. 8278, 82781T, 2012.
[15] Y.-C. Yao( 姚 詠 祺 ), M.-T. Tsai, Y.-J. Lee*, Y.-C. Chen, and C.-J. Wu*,
“Dependence of efficiency-droop effect on the location of high indium layer in staggered InGaN quantum wells,” Journal of Electromagnetic Waves and Applications, Vol. 25, 2442-2453, 2011. (IF: 2.965; Ranking: 18/244=7.3% in Engineering, Electrical & Electronic)
Conference Paper
[1] Yung-Chi Yao(姚詠祺) (Oral), Chun-Ying Huang, Tai-Yuan Lin, Li-Lien Cheng, Ching-Yun Liu, Mei-Tan Wang, Jung-Min Hwang, and Ya-Ju Lee*, “Manipulation of polarization effect to engineer III-nitride HEMTs operation for normally-off,”
The 3rd International Symposium on Next-Generation Electronics (ISNE 2014), Chang Gung University, Taoyuan, Taiwan, 7-10 May, 2014. (榮獲 Best Student
Paper Award)
[2] Yung-Chi Yao(姚詠祺), Chun-Ying Huang, Tai-Yuan Lin, Ching-Yun Liu, Li-Lien Cheng, Mei-Tan Wang, Jung-Min Hwang, and Ya-Ju Lee*, “High breakdown voltage in AlGaN/GaN HEMTs by using AlGaN/GaN/AlGaN quantum-well electron–blocking–layer for power-switching applications,” The 3rd International Symposium on Next-Generation Electronics (ISNE 2014), Chang Gung University, Taoyuan, Taiwan, 7-10 May, 2014.
[3] Yung-Chi Yao(姚詠祺) (Oral), An-Fan Liu, Min-De Yang, Jiun-Tsuen Lai, and Ya-Ju Lee*, “Tailoring the solar spectrum by CdSe quantum dots to enhance the power conversion of triple-junction tandem cells,” Annual Meeting of the Physical Society of ROC (中華民國物理年會), National Chung Hsing University, Taichung
City, Taiwan, 21-23 Jan, 2014. (榮獲優秀口頭發表佳作)
[4] Yung-Chi Yao( 姚 詠 祺 ), Meng-Tsan Tsai, Chun-Ying Huang, Tai-Yuan Lin, Jinn-Kong Sheu, and Ya-Ju Lee*, “Efficient Collection of Photogenerated Carriers by Inserting Double Tunnel Junctions in III-nitride p-i-n Solar Cells,” Annual Meeting of the Physical Society of ROC (中華民國物理年會), National Chung Hsing University, Taichung City, Taiwan, 21-23 Jan, 2014.
[5] Yung-Chi Yao(姚詠祺) (Oral), An-Fan Liu, Min-De Yang, Jiun-Tsuen Lai, and Ya-Ju Lee*, “Tailoring the solar spectrum by CdSe quantum dots to enhance the power conversion of triple-junction tandem cells,” Optics & Photonics Taiwan, International Conference (OPTIC), National Central University, Zhongli, Taiwan, 5-7 Dec, 2013.
[6] Ya-Ju Lee*, Yung-Chi Yao(姚詠祺), and Chia-Hao Yang, “Direct electrical contact of slanted ITO film on axial p-n junction silicon nanowire solar cells,” Conference on Lasers and Electro-Optics: 2013, San Jose, CA, USA, 9-14 June, 2013.
[7] Yung-Chi Yao( 姚 詠祺 ) (Oral), Chia-Hao Yang, and Ya-Ju Lee*, “DIRECT Nanoelectronics Conference (IEEE INEC 2014), Resorts World Sentosa, Singapore, 2-4 Jan, 2013. (國科會補助)
[9] Yung-Chi Yao(姚詠祺) (Oral), Li-Wei She, Chun-Mao Cheng, Yi-Ching Chen, and Ya-Ju Lee*, “Adoption of 2D-nanorod arrays with slanted ITO film to enhance optical absorption for photovoltaic applications,” International Conference on Solid State Devices and Materials (SSDM 2012), Kyoto, Japan, 25-27 Sep, 2012. (台師 大研究發展處補助)
[10] Yung-Chi Yao( 姚 詠 祺 ) (Oral), Po-Wei Lu, and Ya-Ju Lee*, “Effect of geometrical profile of nanostructured arrays on the enhanced optical absorption of silicon thin-film solar cells,” International Conference on Solid State Devices and
Materials (SSDM 2012), Kyoto, Japan, 25-27 Sep, 2012. (台師大研究發展處補 助)
[11] Yung-Chi Yao(姚詠祺) , Li-Wei She, Chun-Mao Cheng, Yi-Ching Chen, and Y. J.
Lee*, “The use of two-dimensional nanorod arrays with slanted ITO film to enhance optical absorption for photovoltaic applications,” E-MRS 2012 Spring meeting, Strasbourg, France, 14-18 May, 2012.
[12] Y.-C. Yao(姚詠祺), Y.-C. Chen, Ya-Ju Lee*, “Dependence of efficiency-droop effect on the location of high indium layer in staggered InGaN quantum wells,”
SPIE Photonics West 2012, San Francisco, California, USA, 21-26 Jan, 2012. (國 科會補助)
[13] 呂柏緯, 姚詠祺, 李亞儒*。比較不同表面奈米結構之光學吸收對矽晶薄膜太 陽能電池之應用。2012 中華民國物理年會暨成果發表會。民國 101 年 01 月 17 日~19 日於國立中正大學舉辦。
[14] Yung-Chi Yao(姚詠祺) (Oral) , Li-Wei She, Chun-Mao Cheng, Yi-Ching Chen, and Y. J. Lee*, “The use of two-dimensional nanorod arrays with slanted ITO film to enhance optical absorption for photovoltaic applications” Annual Meeting of the Physical Society of ROC (中華民國物理年會), National Chung Cheng University, Taiwan,17-19 Jan, 2012.
[15] Chia-Hao Yang, Yung-Chi Yao(姚詠祺), Chun-Mao Cheng, and Y. J. Lee*,
“Enhanced conversion efficiency of InGaN multiple quantum well solar cells grown on a patterned sapphire substrate,” Annual Meeting of the Physical Society of ROC (中華民國物理年會), National Chung Cheng University, Taiwan,17-19 Jan, 2012.
[16] Chia-Hao Yang, Yung-Chi Yao(姚詠祺), Chun-Mao Cheng, and Y. J. Lee*,
“Enhanced conversion efficiency of InGaN multiple quantum well solar cells grown on a patterned sapphire substrate,” International Photonics Conference (光 電年會), National Cheng Kung University, Taiwan, 8-10 Dec, 2011.
[17] Chia-Hao Yang, Yung-Chi Yao(姚詠祺), Chun-Mao Cheng, Min-Hung Lee and Y.
J. Lee*, “InGaN/GaN solar cells grown on wet-etched patterned sapphire substrates,” International Conference on Solid State Devices and Materials, Nagoya,
Japan, 28-30 Sep, 2011.
Awards & Honors
2014 榮獲第三屆 IEEE ISNE 2014 口頭發表【Best Student Paper Award】
2014 榮獲中華民國物理年會優秀口頭發表【佳作】
2013 榮獲國立台灣師範大學一 O 一學年度理學院【研究生參與學術活動優良獎】
2012 榮獲國立台灣師範大學一百學年度【理學院博士班優良論文獎】
2012 榮獲國立台灣師範大學一 O 一學年度【第一學期博士班書卷獎】
2011 榮獲中華民國【斐陶斐榮譽會員】
2011 榮獲國立台灣師範大學一百學年度【第一學期碩士班書卷獎】
2011 榮獲國立台灣師範大學九十九學年度【第二學期碩士班書卷獎】