슬라이드 1

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2 Jung-Ho Lee (PI), Bongyoung Yoo, Jong-Ryoul Kim, Yong-Ho Choa, Yongwoo Cho Hanyang University Collaborated with Yonsei University, KIMM, NNFC, Korea Institute for Energy Research, Sungkyunk wan University, Ewha Women s University

3 Motivation Combining the AR enhancement of dense NWs and the radial p-n junctions of sparse MWs. Tapered SiNWs SiMWs High efficiency solar cell Antireflection (AR) role Ł Enhancement of optical absorption Radial p-n junction of MWs Łutilization of low-purity silicon enabling short diffusion of carriers Very dense tapered NWs co-integrated with periodic MW arrays

4 <Vertically aligned nanowires> Radial p-n junction wired solarcell 1. Strong broadband optical absorption Light trapping enhancement in between nanowires (NWs) 2. More light absorption due to Graded-refractive-index (GRI) effect using tapered NWs < Radial p-n junction microwires> 3. Long absorption paths & short distances for carrier collection Orthogonal separation of carriers to a sunlight direction 4. Large surface areas for light harvest Atwater group, J. Appl. Phys. 97, (2005)

5 Very dense, vertical SiNWs prepared by Ag induced etching Ag deposition Ag induced etching Ag removal P-Si(100) 1-10 ΩCm AgNO3 (0.01M) + HF(4.6M) HF(4.6M) + H 2 O 2 (0.44M) 20min (0.5 um/min) Ag removal nitric acid Deposition of Ag particles Ag induced vertical etching Agglomeration Simple, Cost-effective, Room temperature approach Waferscale fabrication of vertical SiNWs with a nm diameter range Highly uniform feature across the wafer Easy agglomeration at the tops of NWs upon drying

6 Sharp tip, tapered SiNWs KOH etching Top-sides of SiNWs agglomerate to form a bundle Tapered SiNWs 5 5 Effect of KOH etching: SiNW arrays agglomerated by a van der waals force could be easily separated while making their tops very sharp

7 Fabrication of tapered SiNW, SiMW+SiNW, and SiMW (A) Process 1 *Electroless Etching (EE) KOH etching Ag nanoparticle KOH (100) The faster etching P-Si(100) EE (110) SiNW Tapered SiNW (B) Process 2 PR P-Si(100) EE KOH KOH SiMW + NW SiMW

8 Morphological variation of tapered SiNWs with KOH etching time 0s 10s 15s 30s Increasing the KOH etching time Faster etching region (111) KOH etching rate at RT: 24nm/min for (100), 35nm/min for (110) (100) (110) Initially, the corner sides of NWs strongly attacked by KOH because the complicated high-index surfaces develop easily. Finally, sharp-tip, tapered SiNW arrays with (111) side planes remains because the etching rate of those planes is slowest.

9 Co-integrated wire structure of SiNW+SiMW KOH 0s KOH 120s KOH KOH MW + NW KOH 240s KOH MW + tapered NW KOH 180s KOH MW KOH MW + tapered NW

10 Waferscale uniformity of the co-integrated wire structure 4in wafer top bottom Black surface center

11 Doping method: Spin-on-doping (SOD) Fabrication of p-n junction Si dummy wafer Phosphorous-SOD P 2 O 5 SiO 2 <Doping mechanism of psod> P 2P 2 O 5 + 5Si 5SiO 2 + 4P Solid-state diffusion: Predeposition followed by drive-in

12 Bulk or radial p-n junction forms depending upon wire diameters Dummy wafer Phosphorous-SOD Fabrication of p-n junction using SOD Boron-SOD Dummy wafer Tapered SiNWs Bulk p-n junction Concentration (atoms/cc) Phosphorous (top) Boron (bottom) Sputter Depth (nm) SiMWs MWs+NWs Radial p-n junction Radial and bulk p-n junction

13 Low-voltage SEM images of a radial p-n junction MW v v LVSEM images clarify the formation of a radial p(core)-n(shell) junction inside the Si wire. The vanishing contrast at high accelerating voltage is due to the dominance of the energetic backscattered electrons (BSE) and their respectively generated SEs. Concentration(atoms/cc) B P Sputter Depth(nm)

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15 Accelerating Voltage, dopant contrast Contrast can be obtained between kv

16 Electron beam current, dopant contrast Contrast can be obtained between μa

17 Optical property of various wire morphologies Tapered SiNWs 40 5 SiNWs+MWs 5 50 SiMW 5 Reflectance (%) Si(001) substrate Tapered SiNW SiNWs+MWs SiMW Wavelength (nm) 50 The optical absorption of SiNWs+MWs structure is almost same as that of tapered SiNWs.

18 Additional Doping: Plasma Ion Doping (PID) DC bias Pulsed 1kV Dopant PH 3 30 sccm RF power Time Annealing Dose 1kHz 60s 900 C 30sec 3e15 Intensifying the N+-level of the MW shells while enabling shallow, conformal doping p-type wafer

19 Effect of plasma ion doping with SOD SOD 0-5 PID SOD + PID Concentration (atoms/cm3) Junction depth: 10~15nm Depth (nm) J (ma/cm 2 ) SOD V (mv) SOD+PID AM 1.5 (1000W/m 2 ) Additional PID further increases the conversion efficiency by enhancing the n+ doping level of MW shells.

20 J (ma/cm 2 ) V (mv)

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22 83 um 60 um 23 um 80 um

23 Detachment of PDMS embedded wire array Flexible solar cell application PDMS Si wire embedded PDMS Asorption (%) Wavelength (nm)

24 Si v v m

25 Reflectance (%) R,10g T10g R,15g T,10g Transmittance (%) Absorption (%) A,10g A,15g Waveletngh (nm) Wavelength (nm) v The reflectance, transmittance, and absorption spectra of PDMS film show its possibility to solar cell application. v v An excellent light absorption of 90% is occurred in the NIR region. Accordingly, the incident light wave can easily penetrate through the PDMS film, reaching the Si wire arrays and interacting with it.

26 Reflection (%) Absorption (%) Wavelength (nm) Transmission (%) Wavelength (nm) PDMS/SiNWs ((L~4 mm) w/si sub PDMS/SiNWs (L~4 mm) w/o sub PDMS/SiNWs (L~12 mm) w/o sub PDMS/SiNWs (L~16 mm) w/o sub PDMS PDMS Wavelength (nm) SiNW SiNW

27 Formation of P+ emitter p + -Si; I layer by PECVD electr on electr on CdSe or CGTS or Ge n-si Low impurity i-si NNLT 5, 1081 (2005) Ge effect Ge NP on Si MW ( ) Appl. Phys. Lett., 83, 1258 (2003)

28 Pioneer Research Center for Solar Thermal Conversion Nanodevices Jung-Ho Lee (PI), Bongyoung Yoo, Jong-Ryoul Kim Hanyang University Collaborated with Kyu-Hwan Lee (KIMS), Youngkyoo Kim (Kyoungpook National University), Jaehyu n Kim (DGIST), Hyoung-Koun Cho (Sungkyunkwan University), Dongwook Kim (E wha Women s University), Minwook Oh (KERI), Nosang V. Myung (UCRiverside), Choongho Yu (Texas A&M University)

29 v v

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31 Current PV-TE convergence Next-generation version AM1.5 spectrum TE : < PV : λ C2 TE : > AM1.5 spectrum PV-TE λ C1 λ C2 solar spectrum splitter PV hν TE η PV η TE η PV η TE η TE > η TE )

32 v v v

33 PV & TE device Si wired solar cell, Si BiTe nanostructured TE BiTe,,,

34 Thank you for your attention!