Supporting Information for
Tandem-structured, Hot Electron Based Photovoltaic Cell with
Double Schottky Barriers
Young Keun Lee1,2, Hyosun Lee1,2 and Jeong Young Park1,2,*
1
Center for Nanomaterials and Chemical Reactions, Institute for Basic Science, Daejeon
305-701, South Korea
2
Graduate School of EEWS and NanoCentury KI, KAIST, Daejeon 305-701, South Korea
Keywords: metal-semiconductor Schottky diode, internal photoemission, double Schottky
barriers, hot electron, solar cell, surface plasmon
*
To whom correspondence should be addressed. E-mail: jeongypark@kaist.ac.kr
1
Fitting of the thermionic emission equation for the Schottky barrier height, ideality
factor, and series resistance.
b
Au/Si
-4
In I
Thermionic emission fitting
In (Current (A))
In (Current (A))
a
-5
SBH : 0.816 eV
n : 1.15
Rs : 230 ohm
-6
0.21
0.24
0.27
0.30
In I
Thermionic emission fitting
-5
SBH : 0.842 eV
n : 1.01
Rs : 395 ohm
-6
0.33
Tandem structrued TiO2/Au/Si
-4
0.21
Voltage (V)
0.24
0.27
0.30
0.33
Voltage (V)
Figure S1. Fitting I–V curves of (a) the Au/Si and (b) the tandem-structured TiO2/Au/Si to
the thermionic emission equation. After modification from Au/Si to the tandem-structured
TiO2/Au/Si, slight changes in the Schottky barrier height (SBH), ideality factor (n), and series
resistance (Rs) were observed.
Figure S1 shows the electrical characteristics of the Au/Si and the tandem-structured
TiO2/Au/Si diodes, which were investigated by fitting the I–V curves to the thermionic
emission equation. For thermionic emission over the barrier, the current of the Schottky
contacts, as a function of applied voltage, is given by
where F is the area, A* is the effective Richardson constant, Φn is the Schottky barrier height,
η is the ideality factor, and Rs is the series resistance. The effective Richardson constant for
silicon is 120 A/cm2K.
2
Optical properties of the 10 nm thick Au film and TiO2 layers
b
Absorbance (a.u.)
0.8
0.6
Au 10 nm
TiO2 deposited Au 10 nm
TiO2
0.4
0.2
0.0
Gap of absorbance (a.u.)
a
0.3
Au 10 nm - TiO2 deposited
Au 10 nm
0.2
0.1
0.0
400 500 600 700 800 900 1000 1100
400
Wavelength (nm)
500
600
700
800
Wavelength (nm)
Figure S2. (a) UV–Vis spectra of the 10 nm thick gold film (black line), the TiO2-deposited
Au film (red line) and TiO2 film on quartz (green line). After deposition of TiO2 on the gold
film, more incident light penetrates through the TiO2/Au film into the silicon. (b) The gap of
absorbance spectra obtained by subtracting the absorbance spectrum of the TiO2-deposited 10
nm Au film from that of the 10 nm Au film, representing an increased transmitted light
toward the silicon.
To confirm the optical properties of the Au film, the TiO2-deposited Au film, and the
TiO2 film on quartz, absorbance spectra were measured using a UV–vis spectrometer. In the
case of the TiO2-deposited, 10 nm thick Au film on quartz, the absorbance spectrum
decreased in visible light compared with the 10 nm thick Au film case, as shown in Figure
S2a. However the TiO2 film on quartz exhibited a small fraction of the absorption of incident
light. Figure S2b shows the gap of absorbance spectra obtained by subtracting the absorbance
spectrum of the TiO2-deposited, 10 nm thick Au film from that of the 10 nm thick Au film,
revealing an increased transmitted light toward the silicon.
3
Characteristics of solar cell performance under AM 1.5G
a
0.45
b
Fill Factor
0.40
0.40
Voc (V)
0.35
0.35
0.30
0.30
0.25
c
50
40
30
20
10
d
2
Jsc (mA/cm )
6
Efficiency (%)
5
4
3
2
Figure S3. Characteristics of solar cell performance under AM 1.5G: (a) Fill factor, (b) opencircuit voltage, (c) short-circuit current, and (d) solar cell efficiency.
4
Current-Voltage characteristics of Au/TiO2 and TiO2/Au/TiO2 diodes
8
Au (thin film)/TiO2 diode
Au island/TiO2 diode
TiO2/Au/TiO2 tandem cell
Current (mA)
6
4
2
0
-1.0
-0.5
0.0
0.5
1.0
Voltage (V)
Figure S4. I-V curves measured on Au/TiO2 diodes before and after annealing and deposition
of TiO2, indicating that the rectifying behaviors of the diodes were well maintained.
5
6