onur ergen “ “ coaxial silicon nanowires as solar cells and nanoelectronic power sources”...
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Onur Ergen
“Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources”
EE235
Student Presentation 2 march 2009
Electirical Engineering and computer science University of California, Berkeley
OutlineLiterature review: “Coaxial Silicon
Nanowires as Solar Cells and Nanoelectronic Power Sources”
Advantage of this core/shell architecture.
Diode characteristic of p-i-n nanowire core shell strucuture.
Photovoltaic properties of the p-i-n coaxial silicon nanowire diodes.
Silicon p-i-n Nanowires
Advantage of this core/shellstructure,
◦ Charge separation along radial vs.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.
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.
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.
Tunnelling or leakage currents are more significiant for p-n
IV Curves
Tian, B.; Zheng, X.; Kempa, T.; Fang, Y.; Yu, N.; Yu, G.; Huang, J.; Lieber, C. M. Nature, 2007, 449, 885-890.
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%
Radial and axial p-i-n structural
JscRadial =24 mA cm-2
JscAxial =3.5 mA cm-2
VocRadial = 0.26VVocAxial =0.29 V Efficiencies ;ηRadial =3.4%ηAxial =0.5%,
Radial and Axial Single Nanowire Photovoltaics,
B. Tian, T.J. Kempa and C.M. Lieber, "Single Nanowire Photovoltaics," Chem. Soc. Rev. 38, 16-24 (2009)
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 of p-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.
Supplementary Nanowire pH sensor
Capacitance Equations of Core shell
Capacitance Equations of Core shell