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Nanowire Solar Cells

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Nanowire Solar Cells

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Nanowire Solar Cells

  1. 1. Research Project EE663 (Optoelectronic Devices) Fall 2013 Topic: Nanowire Solar Cells By: Hojjatollah Sarvari Department of electrical & Computer Engineering School of Engineering University of Kentucky, Lexington, KY Dec 20, 2013
  2. 2. Outline 2 I. Introduction II. Theory III. Fabrication Procedure IV.Existing Devices (Design & Performance) V. Challenges and Suggestions VI.References Friday Dec 20, 2013
  3. 3. • Nanowires are nanostructures with diameter in range of nanometer. Ratio of the length to width greater than 20. • Many different types of nanowires: Metallic (Ni, Pt, Au) Semiconducting (Si, InP, GaN) and Insulating (SiO2, TiO2) • They are referred to as one-dimensional (1-D) materials. This is because electrons in nanowires are quantum confined laterally and thus occupy energy levels that are different from the traditional continuum of energy levels. I. Introduction 3 Friday Dec 20, 2013
  4. 4. 4 (a & c ) Measured (b & d) Simulated I. Introduction Nanowire Solar Cells Erik C. Garnett et al., Annual. Rev. Mater. Res. 2011. 41:269–95 Friday Dec 20, 2013
  5. 5. 5  There are two types of NW solar cells such as single NW solar cells and array of NW solar cells.  In 2007, a first radial NW Solar Cell was fabricated from an individual silicon nanowire and integrated on-chip to drive the nanowire sensor.  It is obvious that an array of NWs can absorb sunlight more efficient than a single NW due to more space area provided by arrays of NW. I. Introduction Friday Dec 20, 2013
  6. 6. 6 Axial junctions lose the radial charge separation benefit Substrate junctions lack the radial charge separation benefit I. Introduction Nanowire Solar Cells Erik C. Garnett et al., Annual. Rev. Mater. Res. 2011. 41:269–95 Friday Dec 20, 2013
  7. 7. 7 II. Theory Boundary conditions for structure Current density J. The whole device model is calculated in a self-consistent way by using the finite- element method (FEM). Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon Ningfeng Huang et al., Journal Of Applied Physics 112, 064321 (2012) Friday Dec 20, 2013 Position-dependent Absorption where FDTD for electric field Current Continuity equations Poisson’s equation Position-dependent carrier generation rate I is solar irradiation AM1.5D
  8. 8. 8 III. Fabrication Procedure and Challenges Nanowire solar cell fabrication consist of three steps: Nanowire synthesis Junction formation Contacting Nanowires are commonly grown by vapor-liquid-solid (VLS) process, electrochemical deposition into nanoporous templates and solution growth. Two techniques most commonly used in fabrication of nanowire solar cells: Chemical vapor deposition (CVD) Patterned chemical etching Challenge: Large-scale production of the nanowires into highly controlled arrays with high uniformity. Nanowire Solar Cells Erik C. Garnett et al., Annual. Rev. Mater. Res. 2011. 41:269–95 Friday Dec 20, 2013
  9. 9. 9 IV. Existing Devices (Design & Performance) Performance of a solar cell is often measured by factors of Jsc, Voc, and Isc. In order to improve the performance of NW solar cells a number of new geometries cross-sections have been recommended for NW SCs. Circular cross-section Rectangular cross-section Triangular cross-section Hexagonal cross-section Friday Dec 20, 2013
  10. 10. 10 IV. Existing Devices (Design & Performance) Rectangular cross-sectional gallium arsenide (GaAs) NW solar cell Enhancing light absorption and conversion by improving Qabs W : Width of the photoactive rectangle Ds : Thickness of the shell (a) without nanoshell (b) with dielectric nanoshell. Enhanced external quantum efficiency in rectangular single nanowire solar Cells Xiaofeng Li et al., Applied Physics Letters 102, 021101 (2013) Friday Dec 20, 2013
  11. 11. 11 IV. Existing Devices (Design & Performance) (c) and (d) Qabs vs. W Qabs spectra with two W values [(e) and (f) where 125nm for and 250nm for ] (c) and (e) for TE incidence (d) and (f) for TM incidence Enhanced external quantum efficiency in rectangular single nanowire solar Cells Xiaofeng Li et al., Applied Physics Letters 102, 021101 (2013) Friday Dec 20, 2013
  12. 12. 12 IV. Existing Devices (Design & Performance) Optical and electrical characteristics of asymmetric nanowire solar cells Myung-Dong Ko et al., Journal Of Applied Physics 111, 073102 (2012) Radial NW (R-NW) solar cell Asymmetric Radial NW (AS-NW) solar cell p-type (boron) core n-type (phosphorus) shell The core diameter (D) The shell thickness (TS) Friday Dec 20, 2013
  13. 13. 13 IV. Existing Devices (Design & Performance) A larger diameter leads to higher absorption in the low photon energy regime due to a decrease in transmission In the high photon regime, a small diameter leads to high absorption due to lower reflectance Because the effect of the low photon energy is dominant for calculating the overall absorption, the larger incident region gives high light absorption. Optical and electrical characteristics of asymmetric nanowire solar cells Myung-Dong Ko et al., Journal Of Applied Physics 111, 073102 (2012) Friday Dec 20, 2013
  14. 14. 14 IV. Existing Devices (Design & Performance) Optical and electrical characteristics of asymmetric nanowire solar cells Myung-Dong Ko et al., Journal Of Applied Physics 111, 073102 (2012) Friday Dec 20, 2013 Radial NW SC
  15. 15. 15 IV. Existing Devices (Design & Performance) Optical and electrical characteristics of asymmetric nanowire solar cells Myung-Dong Ko et al., Journal Of Applied Physics 111, 073102 (2012) Friday Dec 20, 2013
  16. 16. 16 IV. Existing Devices (Design & Performance) Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon Ningfeng Huang et al., Journal Of Applied Physics 112, 064321 (2012) The nanowires form a vertically aligned hexagonal array. Silicon Substrate It is assumed that each subcell (nanowire array) contains a p-n junction, and that the two subcells are connected in series. Friday Dec 20, 2013
  17. 17. 17 IV. Existing Devices (Design & Performance) Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon Ningfeng Huang et al., Journal Of Applied Physics 112, 064321 (2012) Considered four different III-V materials for the nanowire array, each with different band gap energy: InP 1.34 eV GaAs 1.43 eV Al0.2Ga0.8As 1.72 eV Ga0.5In0.5 P 1.9 eV The highest limiting efficiency (45.3%) occurs when the band gaps of the top and bottom subcells are 1.57eV and 0.935eV, respectively. Friday Dec 20, 2013
  18. 18. 18 IV. Existing Devices (Design & Performance) Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon Ningfeng Huang et al., Journal Of Applied Physics 112, 064321 (2012) (a) Efficiency as a function of nanowire height (b) Efficiency as a function of nanowire band gap energy Friday Dec 20, 2013
  19. 19. 19 IV. Existing Devices (Design & Performance) Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon Ningfeng Huang et al., Journal Of Applied Physics 112, 064321 (2012) (a) lattice constant (b) d/a ratio (c) diameterFriday Dec 20, 2013 Optimal structural parameters for different materials
  20. 20. 20 IV. Existing Devices (Design & Performance) Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon Ningfeng Huang et al., Journal Of Applied Physics 112, 064321 (2012) Junction designs for III-V NW on silicon cells with (a) Radial junction (b) Axial junction in the nanowire. (c) Carrier generation rate profile in GaAs nanowire Friday Dec 20, 2013
  21. 21. 21 IV. Existing Devices (Design & Performance) Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon Ningfeng Huang et al., Journal Of Applied Physics 112, 064321 (2012) (a) Radial junction (b) Axial junction GaAs nanowire top cell. (c) J-V curves for axial and radial junction geometries for varying SRV. Friday Dec 20, 2013 Surface Recombination Velocity
  22. 22. 22 IV. Existing Devices (Design & Performance) Numerical Simulation of Light-Trapping and Photoelectric Conversion in Single Nanowire Silicon Solar Cells Yaohui Zhan et al., IEEE Journal Of Selected Topics In Quantum Electronics, VOL. 19, NO. 5, (2013) Cylindrical single nanowire solar cell (SNSC) Under solar illumination with TE or TM polarization Friday Dec 20, 2013 p-type core (diameter 110 nm) intrinsic layer (thickness 40 nm) n-type shell (thickness 60 nm).
  23. 23. 23 IV. Existing Devices (Design & Performance) Effects of doping Friday Dec 20, 2013 Numerical Simulation of Light-Trapping and Photoelectric Conversion in Single Nanowire Silicon Solar Cells Yaohui Zhan et al., IEEE Journal Of Selected Topics In Quantum Electronics, VOL. 19, NO. 5, (2013)
  24. 24. 24 IV. Existing Devices (Design & Performance) Effect of i-layer thicknesses Friday Dec 20, 2013 Numerical Simulation of Light-Trapping and Photoelectric Conversion in Single Nanowire Silicon Solar Cells Yaohui Zhan et al., IEEE Journal Of Selected Topics In Quantum Electronics, VOL. 19, NO. 5, (2013)
  25. 25. 25 IV. Existing Devices (Design & Performance) Optical and electrical simulations of two-junction III-V nanowires on Si solar cell Shaojiang Bu. et al., Appl. Phys. Lett. 102, 031106 (2013) Friday Dec 20, 2013 NWs with length of 2 micrometer Si substrate with thickness 400 nm. Period of the square lattice P NWs diameter D Filling ratio D/P The NWs are composed of Ga0.35 In0.65 P with bandgap of 1.7 eV. Two-junction III-V GaInP NWA/Si thin film solar cell
  26. 26. 26 IV. Existing Devices (Design & Performance) Optical and electrical simulations of two-junction III-V nanowires on Si solar cell Shaojiang Bu. et al., Appl. Phys. Lett. 102, 031106 (2013) The maximum efficiency is 34.3% with FF=0.6 and D=200 nm Higher filling ratio (D/P) of NWA means more consumption of Ga and In elements. Friday Dec 20, 2013
  27. 27. 27 IV. Existing Devices (Design & Performance) Optical and electrical simulations of two-junction III-V nanowires on Si solar cell Shaojiang Bu. et al., Appl. Phys. Lett. 102, 031106 (2013) The Jsc decreases substantially from 17.78 to 15.62mA/cm2, when SRV increases from 0 to 5*106 cm/s. At non-ideal conditions (SRV=7*104 cm/s), the net J-V characteristic yielded Jsc=17.1 mA.cm-2, Voc=1.837 V, FF=0.86, and g=27.1%. The maximum efficiency is 34.3% with FF=0.6 and D=200 nm Friday Dec 20, 2013
  28. 28. 28 V. Challenges and Suggestions NWs Reduce the quantity and quality of material necessary to approach those limits which allowing for substantial cost reductions. NWs provide opportunities to fabricate complex single-crystalline semiconductor devices directly on low-cost substrates and electrodes such as aluminum foil and conductive glasses. Many materials relevant to solar cells, including zinc oxide, germanium, silicon, indium gallium nitride and cadmium sulfide. Some challenges in the field of nanowire solar cells that include:  Surface and interface recombination  surface roughness  mechanical and chemical stability  doping control  nanowire array uniformity Friday Dec 20, 2013
  29. 29. 29 V. Challenges and Suggestions Silica substrates will slightly degrade the absorption efficiency of SNSCs, while metal substrates will greatly enhance the absorption performance. Rectangular cross section nanowire has the greatest absorption efficiency among all the geometries Increase with the number of NW in a parallel array for Jsc Synthesis methods such as VLS it is possible to very accurately control nanowire architecture including: size, morphology and material. As a suggestion: Multi-junction (two or three multi-junction) nanowire array solar cells with rectangular geometry on glass or metallic substrates with fabrication methods such as VLS. Friday Dec 20, 2013
  30. 30. 30 VI. References 1. Shaojiang Bu. et al., Optical and electrical simulations of two-junction III-V nanowires on Si solar cell, Appl. Phys. Lett. 102, 031106 (2013) 2. Yaohui Zhan et al., Numerical Simulation of Light-Trapping and Photoelectric Conversion in Single Nanowire Silicon Solar Cells, IEEE Journal Of Selected Topics In Quantum Electronics, VOL. 19, NO. 5, (2013) 3. Xiaofeng Li et al., Enhanced external quantum efficiency in rectangular single nanowire solar Cells, Applied Physics Letters 102, 021101 (2013) 4. Myung-Dong Ko et al., Optical and electrical characteristics of asymmetric nanowire solar cells, Journal Of Applied Physics 111, 073102 (2012) 5. Ningfeng Huang et al., Limiting efficiencies of tandem solar cells consisting of III-V nanowire arrays on silicon, Journal Of Applied Physics 112, 064321 (2012) 6. Erik C. Garnett et al., Nanowire Solar Cells, Annual. Rev. Mater. Res. 2011. 41:269–95 Friday Dec 20, 2013
  31. 31. 31 Friday Dec 20, 2013

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