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Onur Ergen

“ Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources”. Onur Ergen. Electirical Engineering and computer science University of California, Berkeley onur@eecs.berkeley.edu. EE235 Student Presentation 2 march 2009. Outline.

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Onur Ergen

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  1. “Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources” Onur Ergen Electirical Engineering and computer science University of California, Berkeley onur@eecs.berkeley.edu EE235 Student Presentation 2 march 2009

  2. Outline • Literature review: “Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources” • Advantage of this core/shell architecture. • Diode characteristic of p-i-nnanowire core shell strucuture. • Photovoltaic properties of the p-i-n coaxial silicon nanowire diodes.

  3. Silicon p-i-nNanowires • Advantage of this core/shellstructure, • Charge separation along radialvs.longer axial direction • Photo generated carriers can reach the p-i-n junction without bulk recombination. • Material quality can be lower • Grown by VLS followed by CVD • Single crystalline core, polycrystalline shell Tian, B.; Zheng, X.; Kempa, T.; Fang, Y.; Yu, N.; Yu, G.; Huang, J.; Lieber, C. M. Nature, 2007, 449, 885-890.

  4. Contact Formation by using Lithography Tian, B.; Zheng, X.; Kempa, T.; Fang, Y.; Yu, N.; Yu, G.; Huang, J.; Lieber, C. M. Nature, 2007, 449, 885-890.

  5. Diode characteristic • Highly conductive n-shell eliminate potential drop along the shell, • enabling carrier separation and collection when illuminated. • “ ‘AND’ and ‘OR’ diode logic gates. • Ideality factor N , • Np-i-n=1.96 for Np-n=4.52 • p-i-n diode breaks down much larger. • Low temperature high breakdown voltage. • Tunnellingor leakage currents are moresignificiant for p-n

  6. IV Curves • Illuminated under AM1.5 conditions • Voc = 0.260V; • V is essentially independent of length. • Isc = 0.503 nA; • Ffill= 55.0 % • Maximum Power = 72 pW, stable for seven months • Power Conversion Efficiency = ~ 3% Tian, B.; Zheng, X.; Kempa, T.; Fang, Y.; Yu, N.; Yu, G.; Huang, J.; Lieber, C. M. Nature, 2007, 449, 885-890.

  7. Radial and Axial Single NanowirePhotovoltaics, Radial and axial p-i-n structural JscRadial=24 mA cm-2 JscAxial =3.5 mA cm-2 VocRadial= 0.26V VocAxial=0.29 V Efficiencies ; ηRadial =3.4% ηAxial =0.5%, B. Tian, T.J. Kempa and C.M. Lieber, "Single NanowirePhotovoltaics," Chem. Soc. Rev. 38, 16-24 (2009)

  8. Conclusions • Reducing recombination can increase device performance • Nanowire is 6.6 % efficient at 80 K • Possible to used as power sources in nanoelectronics • Nanowire PV was used to drive a nanowire pH sensor without external power. • Controlling the thickness ofp-i-n layers have crucial importance for Voc. Tian, B.; Zheng, X.; Kempa, T.; Fang, Y.; Yu, N.; Yu, G.; Huang, J.; Lieber, C. M. Nature, 2007, 449, 885-890.

  9. Supplementary • NanowirepH sensor

  10. Capacitance Equations of Core shell

  11. Capacitance Equations of Core shell

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