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  Article Characteristics of InGaN-based concentrator solar cells operating under 150X solar concentration Chih-Ciao Yang Chih-Ciao Yang Remove suggestion C H Jang C H Jang Remove suggestion Jinn-Kong Sheu Jinn-Kong Sheu National Cheng Kung University Message author Remove suggestion Ming-Lun Lee Ming-Lun Lee Remove suggestion Shang-Ju Tu Shang-Ju Tu Remove suggestion Feng-Wen Huang Feng-Wen Huang Remove suggestion [more] Institute of Electro-Optical Science & Engineering and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan City 70101, Taiwan. Optics Express (Impact Factor: 3.49). 07/2011; 19 Suppl 4(14):A695-700. DOI: 10.1364/OE.19.00A695 Source: PubMed ABSTRACT InGaN/sapphire-based photovoltaic (PV) cells with blue-band GaN/InGaN multiple-quantum-well absorption layers grown on patterned sapphire substrates were characterized under high concentrations up to 150-sun AM1.5G testing conditions. When the concentration ratio increased from 1 to 150 suns, the open-circuit voltage of the PV cells increased from 2.28 to 2.50 V. The peak power conversion efficiency (PCE) occurred at the 100-sun conditions, where the PV cells maintained the fill factor as high as 0.70 and exhibited a PCE of 2.23%. The results showed great potential of InGaN alloys for future high concentration photovoltaic applications. Figures in this publication Get notified about updates to this publication Follow publication Download full-text Full-text DOI: · Available from: Jinn-Kong Sheu, Jun 16, 2014 Share Page 1 Characteristics of InGaN-based concentrator solar cells operating under 150X solar concentration Chih-Ciao Yang,1 C. H. Jang,2 Jinn-Kong Sheu,1,3,* Ming-Lun Lee,3,4 Shang-Ju Tu,1 Feng-Wen Huang,1 Yu-Hsiang Yeh,4 and Wei-Chih Lai1,3 1Institute of Electro-Optical Science & Engineering and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan City 70101, Taiwan 2Institute of Microelectronics & Department of Electrical Engineering, National Cheng Kung University, Tainan City 70101, Taiwan 3Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan City 70101, Taiwan 4Department of Electro-Optical Engineering, Southern Taiwan University Tainan County 71001, Taiwan *jksheu@mail.ncku.edu.tw Abstract: InGaN/sapphire-based photovoltaic (PV) cells with blue-band GaN/InGaN multiple-quantum-well absorption layers grown on patterned sapphire substrates were characterized under high concentrations up to 150-sun AM1.5G testing conditions. When the concentration ratio increased from 1 to 150 suns, the open-circuit voltage of the PV cells increased from 2.28 to 2.50 V. The peak power conversion efficiency (PCE) occurred at the 100-sun conditions, where the PV cells maintained the fill factor as high as 0.70 and exhibited a PCE of 2.23%. The results showed great potential of InGaN alloys for future high concentration photovoltaic applications. ©2011 Optical Society of America OCIS codes: (040.5350) Photovoltaic; (040.4200) Quantum-well, -wire and -dot devices; (230.0250) Optoelectronics. References and links 1. R. R. King, A. Boca, W. Hong, X. Q. Liu, D. Bhusari, D. Larrabee, K. M. Edmondson, D. C. Law, C. M. Fetzer, S. Mesropian, and N. H. Karam, "Band-gap-engineered architectures for high-efficiency multijunction concentrator solar cells," Proc. 24th Eur. PVSEC, 55–61 (2009). 2. A. D. Vos, Thermodynamics of Solar Energy Conversion, Wiley-VCH, Weinheim, Germany (2008). 3. J. Wu, W. Walukiewicz, K. M. Yu, W. Shan, J. W. Ager III, E. E. Haller, H. Lu, W. J. Schaff, W. K. Metzger, and S. Kurtz, "Superior radiation resistance of In1-xGaxN alloys: full-solar-spectrum photovoltaic material system," J. Appl. Phys. 94(10), 6477–6482 (2003). 4. H. Hamzaoui, A. S. Bouazzi, and B. Rezig, "Theoretical possibilities of InxGa1-xN tandem PV structures," Sol. Energy Mater. Sol. Cells 87(1–4), 595–603 (2005). 5. O. Jani, I. Ferguson, C. Honsberg, and S. Kurtz, "Design and characterization of GaN/InGaN solar cells," Appl. Phys. Lett. 91(13), 132117 (2007). 6. 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). 7. R. Dahal, B. Pantha, J. Li, J. Y. Lin, and H. X. Jiang, "InGaN/GaN multiple quantum well solar cells with long operating wavelengths," Appl. Phys. Lett. 94(6), 063505 (2009). 8. D. M. Chapin, C. S. Fuller, and G. L. Pearson, "A new silicon p-n junction photocell for converting solar radiation into electrical power," J. Appl. Phys. 25(5), 676–677 (1954). 9. D. Jenny, J. Loferski, and P. Rappaport, "Photovoltaic Effect in GaAs p-n Junctions and Solar Energy Conversion," Phys. Rev. 101(3), 1208–1209 (1956). 10. S. Nakamura, "The roles of structural imperfections in InGaN-based blue light-emitting diodes and laser diodes, " Science 281(5379), 955–961 (1998). 11. N. Nepal, M. O. Luen, J. M. Zavada, S. M. Bedair, P. Frajtag, and N. A. El-Masry, "Electric field control of room temperature ferromagnetism in III-N dilute magnetic semiconductor films," Appl. Phys. Lett. 94(13), 132505 (2009). 12. R. Dahal, J. Li, J. Y. Lin, and H. X. Jiang, "InGaN/GaN multiple quantum well concentrator solar cells," Appl. Phys. Lett. 97(7), 073115 (2010). #141643 - $15.00 USD(C) 2011 OSAReceived 24 Jan 2011; revised 21 Feb 2011; accepted 29 Apr 2011; published 18 May 20114 July 2011 / Vol. 19, No. S4 / OPTICS EXPRESS A695 Page 2 13. W. K. Wang, D. S. Wuu, S. H. Lin, P. Han, R. H. Horng, T. C. Hsu, D. T. C. Huo, M. J. Jou, Y. H. Yu, and A. Lin, "Efficiency improvement of near-ultraviolet InGaN LEDs using patterned sapphire substrates," IEEE J. Quantum Electron. 41(11), 1403–1409 (2005) (and references therein). 14. M. L. Lee, J. K. Sheu, and C. C. Hu, "Nonalloyed Cr/Au-based Ohmic contacts to n-GaN," Appl. Phys. Lett. 91(18), 182106 (2007). 15. M. Jeng, Y. Lee, and L. Chang, "Temperature dependences of InxGa1-xN multiple quantum well solar cells," J. Phys. D Appl. Phys. 42(10), 105101 (2009). 16. C. C. Yang, J. K. Sheu, X. W. Liang, M. S. Huang, M. L. Lee, K. H. Chang, S. J. Tu, F. W. Huang, and W. C. Lai, "Enhancement of the conversion efficiency of GaN-based photovoltaic devices with AlGaN/InGaN absorption layers," Appl. Phys. Lett. 97(2), 021113 (2010). 17. C. H. Henry, "Limiting efficiencies of ideal single and multiple energy gap terrestrial solar cells," J. Appl. Phys. 51(8), 4494–4500 (1980). 18. K. Nishioka, T. Takamoto, T. Agui, M. Kaneiwa, Y. Uraoka, and T. Fuyuki, "Evaluation of InGaP/InGaAs/Ge triple-junction solar cell and optimization of solar cell's structure focusing on series resistance for high-efficiency concentrator photovoltaic systems," Sol. Energy Mater. Sol. Cells 90(9), 1308–1321 (2006). 19. K. Araki, M. Yamaguchi, T. Takamoto, E. Ikeda, T. Agui, H. Kurita, K. Takahashi, and T. Unno, "Characteristics of GaAs-based concentrator cells," Sol. Energy Mater. Sol. Cells 66(1–4), 559–565 (2001). 20. G. S. Kinsey, P. Hebert, K. E. Barbour, D. D. Krut, H. L. Cotal, and R. A. Sherif, "Concentrator multijunction solar cell characteristics under variable intensity and temperature," Prog. Photovolt. Res. Appl. 16(6), 503–508 (2008). 1. Introduction High-concentration photovoltaic (HCPV) cells have been widely prepared using group III-V compound semiconductors, such as GaInP/GaInAs/Ge tandem solar cells, to achieve very high efficiency [1]. In PV concentration systems, sunlight is focused by lens or mirrors to increase incident light flux density to deliver more power compared with nonconcentrated systems. When the open-circuit voltage (VOC) of PV cells is logarithmically increased with concentrated sunlight, power conversion efficiency (PCE) is enhanced, and cell cost is reduced by saving the cell area. To achieve even higher efficiency, a single material system of the InxGa1-XN alloys simultaneously covers a wide solar-spectrum range by the combination of InN with GaN compound semiconductors, especially those larger than 2 eV and lower than 1 eV, which could be obtained for specific optimum multi-bandgaps for future tandem cells with ultra-high power conversion efficiency [2–4]. This field has drawn much attention [5–7]. However, there are still few reports on HCPV characteristics of InGaN-based materials. Although the first Si p-n junction solar cell was developed in 1954 [8], GaAs in 1956 [9], and concentrator tandem solar cells and organic PV cells in the 1990's, the group III-nitride semiconductors for PV applications are still in its infancy. To date, the GaN-based materials, mostly grown on sapphire (Al2O3) substrates, have been widely applied to laser diodes, light-emitting diodes, high power convertors, UV-photodetectors, and spintronics recently [10,11]. This is because GaN-based materials have excellent properties, such as tunable bandgap engineering, high mobility, excellent chemical tolerance, superior radiation resistance, self-organized InGaN quantum dots and very high absorption coefficients (> 105 cm1) near the material bandgap [10]. At present, however, there still lacks for suitable substrate to grow III-nitride materials with low structure defect density. Lattice constant and thermal coefficient mismatches induce threading dislocations and high background carrier concentration that limit the performance of InGaN-based PV devices [10]. Dahal et al. reported their efforts on 30-sun concentration levels by a multiple-quantum-well(MQW)-type cell with back metal reflectors. Although the photocurrent was enhanced 15% by the aluminum back reflectors, the fill factor (FF) value significantly decreased by 11% mainly due to serious recombination [12]. In this study, we proposed a blue-band MQW-type PV cell grown on patterned sapphire substrates (PSSs), which could efficiently improve internal quantum efficiency by decreasing the dislocation density [13]. In addition, the surface of PV cells was textured to allow less light reflection thereon. The solar response under concentrated levels up to 150-sun conditions shall be discussed. #141643 - $15.00 USD(C) 2011 OSAReceived 24 Jan 2011; revised 21 Feb 2011; accepted 29 Apr 2011; published 18 May 20114 July 2011 / Vol. 19, No. S4 / OPTICS EXPRESS A696 Page 3 2. Device fabrication and experiment methods InGaN epitaxial layers were deposited on c-face sapphire substrates by a metalorganic vapor-phase epitaxy reactor. The substrate used in this study was PSS through the conventional photolithography and dry etching process. PSS featured truncated cone patterns in the closely triangular package with 3 μm spacing. The top and bottom diameters of the truncated cone were 2 and 3 μm, respectively, and the height was 1.5 μm. Figure 1 shows the schematic structure of the blue-band MQW-type InGaN-based PV cell. The deposition process involved a 30 nm thick low-temperature GaN nucleation layer, followed by a 1.6 μm thick undoped GaN (u-GaN) with chamber pressure at 500 torr and then a 3 μm thick u-GaN at 200 torr. Afterward, a p-i-n heterostructure consisting of 3 μm thick Si-doped n+-GaN (n~5 × 1018 cm3), an undoped InGaN/GaN (2.5/14.5 nm for 10 pairs) multiple quantum well structure, and 200 nm thick Mg-doped p-GaN (p~5 × 1017 cm3) were sequentially deposited. The peak value of the electroluminescence (EL) spectrum of the MQW-type PV cell was characterized at 448 nm. The fabrication process was similar to conventional nitride-based light-emitting diodes (LEDs) with lateral electrode pads. First, a 200 nm thick indium tin oxide (ITO) film prepared by RF sputtering was deposited on p-GaN to form the p-type ohmic contact. The cell area was defined into 1 × 1 mm2 by photolithography. A self-aligned etching process was performed to expose the underlying n+-GaN layer by ITO etching solutions and inductively coupled plasma in sequence. On the ITO surface, circle patterns in the closely triangular package (both diameter and spacing were 5 μm) were formed by selectively etching to reduce light reflection at the cell surface. Afterward, the Cr/Au (50/1000 nm) bilayer metal was deposited on the ITO and the exposed n+-GaN to form the anode and cathode electrode, respectively [14]. The lateral electrode pads were in digitated configurations for better current collection. Finally, a 200 nm thick SiO2 layer was coated using plasma-enhanced chemical-phase deposition to function as the antireflection and passivation layer. Fig. 1. Schematic structure of fabricated InGaN-based PV devices. 3. Results and discussion Figure 2 shows the typical characteristics of current density and power density versus voltage (J-V and P-V, respectively) of MQW-type PV cells illuminated by the solar simulator, which was calibrated by the calibration cell of NREL with global air-mass 1.5 (AM1.5G) testing conditions. The measured VOC, short-circuit current density (JSC) and FF of the PV cell were 2.28 V, 1.27 mA/cm2, and 0.74, respectively, corresponding to the PCE of 2.13%. Under AM1.5G conditions, the experiment results indicated that the photocurrent of our InGaN PV cells reached 63% of the theoretical value (approximately 2.0 mA/cm2). Although this was significantly higher than reported results with similar blue-band InGaN materials [15,16], the PCE was still far from the theoretical value (~4.5%) by single-junction materials with optical bandgap at 2.77 eV (448 nm) [17]. It was mainly limited by material qualities due to the large #141643 - $15.00 USD(C) 2011 OSAReceived 24 Jan 2011; revised 21 Feb 2011; accepted 29 Apr 2011; published 18 May 20114 July 2011 / Vol. 19, No. S4 / OPTICS EXPRESS A697 Page 4 lattice mismatch between sapphire substrates and GaN-based semiconductors [10]. In p-i-n type PV cells with single InGaN absorption layers, the GaN/sapphire hetero-epitaxy limits the critical thickness of InGaN, especially when the indium contents are raised to convert more sunlight. That is, the epitaxial structure could be relaxed to induce leakage to lower the shunt resistance of PV devices. Noteworthly, the VOC value in this study was competatively high enough compared with other similar PV cells with blue-band absorption layers. This could be attributed to the fact that material quality of GaN-based epitaxial layers was improved by the use of PSS [13]. Fig. 2. Typical J-V and P-V characteristics of the MQW-type PV devices illuminated by the AM1.5G conditions. With material properties of high thermal conductivity and low saturation current, PV cells made from InGaN alloys are expected to have excellent potential to operate under high solar concentration. Since GaN-based epitaxial layers are generally grown on sapphire or SiC substrates, mismatch-induced structure defects (e.g. threading dislocations) that play a key role degrade the cell performance. On the other hand, the sapphire substrates with low thermal conductivity may cause further degradation of performance of InGaN-based PV cells operating under high solar concentration. To study the concentrated solar response of MQW-type PV cells made from InGaN/sapphire-based materials, Fresnel lens were used to concentrated light up to 150-sun conditions by the AM1.5G spectrum, and the cell temperature was maintained at 25 °C. Figure 3 shows the typical J-V characteristics under concentrated conditions. In an equivalent circuit of a solar cell modeled by an ideal current source (JSC) in parallel with a diode, the J-V characteristic is given by Eq. (1): ({JJ 0qVnkTexp,)} scJ (1) where n, k, q, T are the ideality factor, Boltzmann constant, elementary charge and absolute temperature, respectively. J0 is the diode saturation current density. From Eq. (1), VOC (J 0) is given by Eq. (2): scoc0JJnkTqV 1n 1 . (2) From Eq. (2), VOC increases logarithmically with JSC (i.e., radiation intensity). Generally, at the high concentration ratio, the measured value of VOC may be smaller than the 1-sun value. This is because cell temperature rises by the light with high energy at the high concentration ratio, and VOC decreases. The decrease in VOC with increasing temperature arises mainly from changes in intrinsic carrier concentration (ni); the value of J0 increases exponentially with decreasing T1, causing VOC to decrease almost linearly with increasing T. The conversion efficiency is thus decreased by the decrease of VOC at the high concentration #141643 - $15.00 USD(C) 2011 OSAReceived 24 Jan 2011; revised 21 Feb 2011; accepted 29 Apr 2011; published 18 May 20114 July 2011 / Vol. 19, No. S4 / OPTICS EXPRESS A698 Page 5 ratio. In this study, the cell temperature was well maintained at 25 °C by using a cooling stage. Therefore, VOC increased logarithmically with radiation intensity although sun concentrations increased to 150. The VOC values increased from 2.28 to 2.50 V, and FF values decreased from 0.74 to 0.70 when the concentrated level was increased from 1- to 150-sun conditions, as shown in Fig. 4(a). Compared with 1-sun illumination, the measured VOC increased by 9.6% and measured FF decreased by 5.4% when the PV cells were tested under 100-sun conditions. This corresponded to an enhancement of PCE by approximately 4.7%. Peak PCE (2.23%) occurred at 100-sun conditions rather than 150-sun conditions, as shown in Fig. 4(b). The PCE rolling off as the sun concentration over 100 could be due to the reduced FF. The lower FF at high concentration could be attributed to the relatively significant power loss compared with low-concentration illumination due to high current. In other words, power consumption in the series resistance (RS) increased with an increase in cell current (i.e., under high illumination) [18]. Therefore, it is important to reduce RS further to allow for GaN-based PV cells operating under high concentration. Fig. 3. Typical J-V characteristics under concentrated levels up to 150-sun conditions. Fig. 4. The summarized solar parameters under concentrated illumination by the AM1.5G spectrum: (a) PCE in semi-logarithmical scales and (b) VOC and FF in linear scales. To extract RS from PV cells, J-V characteristics taken from solar cells under illumination with different concentrations were performed. The RS value of the PV cells was determined to be 23.5 Ωcm2 on average. This RS value was larger than that of conventional PV cells (e.g., InGaP/GaAs/Ge tandem cells). In conventional tandem PV cells, tunneling junctions between subcells dominate RS. In single-junction GaN-based PV cells, InGaN/GaN-based p-i-n heterojunctions have relatively larger band discontinuity and low-conductivity p-GaN contact layer, which result in high RS. In addition, GaN-based tunneling diodes are important to future InGaN/GaN-based tandem cells. However, this research topic is still in its infancy. In addition to the RS issue, the material quality is also important. In conventional PV cells, different #141643 - $15.00 USD(C) 2011 OSAReceived 24 Jan 2011; revised 21 Feb 2011; accepted 29 Apr 2011; published 18 May 20114 July 2011 / Vol. 19, No. S4 / OPTICS EXPRESS A699 Page 6 semiconductor layers with tiny lattice mismatches between them are stacked by heteroepitaxy to form subcells on a substrate in sequence. Generally, the density of structure defects in GaAs-based cells is low enough; thus, performance is reasonably good. InGaN-based PV cells grown on sapphire substrates suffer from large lattice mismatches between III-nitride semiconductors and sapphire. Therefore, dense structure defects (e.g., threading dislocation) in InGaN-based PV cells significantly degrade the device performance. In a fabricated PV diode, extracting the ideality factor from J-V characteristics can be indirectly applied to evaluate the effect of material quality on device performance. The calculated VOC values of PV cells based on different diode ideality factors (n = 2) under different concentrated levels are also shown in Fig. 4(a). In conventional GaAs-based tandem cells, the ideality factor is larger than unity and typically greater than 3. This could be attributed to the epitaxial interface profile and mismatched current in each subcell [19,20]. At low current levels, photogenerated carriers could be possibly recombined by defect centers. At high concentrated levels, the ideality factor increases rapidly with the increase of diode saturation current. In this study, the ideality factor was estimated to be 1.7 at high current levels (i.e., 100-sun concentration conditions) but 2.0 at low current levels (i.e., 10-sun concentration conditions). This indicated that the component of recombination current cannot be ignored in PV cells. In a heterojunction, many factors could result in an ideality factor much greater than 2, including tunneling through barriers, interface defects and charge-related defects with a pined Fermi level [1,12]. This ideality factor was markedly lower than those of our previous GaN-based PV cells grown on flat sapphire substrates [16]. In other words, PSS-grown GaN-based PV cells exhibited positive effect on material qualities and resulted in PCE enhancement. 4. Conclusions We have demonstrated the InGaN-based solar cells operating under high concentrated conditions over 100-sun intensities of the AM1.5G spectrum. This result indicates that the InGaN/sapphire-based PV cells have great potential for HCPV applications. The blue-band MQW-type PV cells were deposited on PSSs and fabricated with a textured surface through selective etching of the ITO top contact layer. VOC values increased from 2.28 to 2.50 V when the concentrated level was increased from 1- to 150-sun conditions, and FF values remained as high as 0.70. PCE was enhanced to 2.23% when PV cells were tested under 100-sun conditions. The PCE rolled off as the sun concentration over 100 could be due to the reduction in FF. The declined FF at high concentration could be attributed to the high series resistance. Acknowledgment This work was financially supported by National Science Council under grant NSC 97-2221-E-006-242-MY3 and 98-2221-E-218-005-MY3, and Center for Micro/Nano Science and Technology of National Cheng Kung University. #141643 - $15.00 USD(C) 2011 OSAReceived 24 Jan 2011; revised 21 Feb 2011; accepted 29 Apr 2011; published 18 May 20114 July 2011 / Vol. 19, No. S4 / OPTICS EXPRESS A700 Download full-text View other sources Hide other sources Characteristics of InGaN-based concentrator solar ... Available from Jinn-Kong Sheu · Jun 16, 2014 Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable. References (18) Cited In (12) Sorted by: Order of availability Order of availability Appearance in publication Source Available from: cpl.iphy.ac.cn Article: High Concentration InGaN/GaN Multi-Quantum Well Solar Cells with a Peak Open-Circuit Voltage of 2.45 V Zhang Dong-Yan · Zheng Xin-He · Li Xue-Fei · Wu Yuan-Yuan · Wang Jian-Feng · Yang Hui [Show abstract] [Hide abstract] ABSTRACT: We report InGaN/GaN multi-quantum well (MQW) solar cells with a comparatively high open-circuit voltage and good concentration properties. The open circuit voltage (Voc) keeps increasing logarithmically with concentration ratio until 60 suns. The peak Voc of InGaN/GaN MQW solar cells, which has a predominant peak wavelength of 456 nm from electroluminescence measurements, is found to be 2.45 V when the concentration ratio reaches 333×. Furthermore, the dependence of conversion efficiency and fill factor on concentration ratio are analyzed. Preview · Article · Jun 2012 · Chinese Physics Letters Request full-text Article: InGaN/GaN Multiple Quantum Well Solar Cells with Good Open-Circuit Voltage and Concentrator Action Xue-Fei Li · Xin-He Zheng · Dong-Yan Zhang · Yuan-Yuan Wu · Xiao-Ming Shen · Jian-Feng Wang · Hui Yang [Show abstract] [Hide abstract] ABSTRACT: The photovoltaic properties of large-chip-size (2.5× 2.5
  mm2) InGaN/GaN multiple quantum well (MQW) solar cells grown
  by metal organic chemical vapor deposition were studied under
  concentrated AM1.5G sun irradiation. We demonstrate a high open-circuit
  voltage of 2.31 V for blue-light-emitting InGaN/GaN MQW solar cells
  under 1 sun. The higher open-circuit voltage is mainly ascribed to the
  extremely low reversed saturation current density of approximately
  10-19 mA/cm2. The open-circuit voltage and
  short-circuit current density were found to increase as sunlight
  intensity increases, with a peak value of 2.50 V observed at 190 suns,
  showing a great potential for concentrator applications. No preview · Article · Sep 2012 · Japanese Journal of Applied Physics Request full-text Article: A concentration photovoltaic system adopting a liquid crystal light modulation Yu-Shih Tsou · Yi-Hsin Lin · An-Chi Wei [Show abstract] [Hide abstract] ABSTRACT: A concentration photovoltaic (CPV) system adopting a liquid crystal
  light modulation is demonstrated. The LC light modulation adjusts the
  optical power density of the incident light based on the electrically
  controllable distribution of LC directors. The electrically tunable
  concentration ratio of the LC light modulation can help to achieve the
  highest and a fixed efficiency of the CPV system because the LC light
  modulation helps to increase the photocurrent at a low illumination and
  prevent the effect of the series resistance at a high illumination. This
  study opens a window in solar cells by using LC light modulations. No preview · Article · Oct 2012 · Proceedings of SPIE - The International Society for Optical Engineering Request full-text Show more Note: This list is based on the publications in our database and might not be exhaustive. View other sources Hide other sources Similar Publications Enhanced efficiency of Cu(In,Ga)Se2 solar cells with antireflection coating layers of MgF2 and ZnO nanorods Bo-Hyun Shim, Jang-Won Kang, Hojung Jeong, Yonkil Jeong, T. Prem Kumar, Jae-Hyung Jang, Seong-Ju Park Photonic flash-annealing of lead halide perovskite solar cells in 1 ms Joel Troughton, Matthew John Carnie, Matthew L. Davies, Cécile Charbonneau, Eifion Jewell, David Anthony Worsley, Trystan M. Watson Insertion of interlayers in efficient polymer-based organic solar cells for control of phase separation Tetsuya Taima, Jun Tanaka, Takayuki Kuwabara, Kohshin Takahashi © 2008‐2016 researchgate.net. All rights reserved. About us · Contact us · Careers · Developers · News · Privacy · Terms | Advertising · Recruiting Join for free Log in Email Password Forgot password? Keep me logged in or log in with ResearchGate is the professional network for scientists and researchers. Join for free