6th U.S.-Korea Forums on Nanotechnology
April 29 2009
FABRICATION OF SI QUANTUM-DOT SOLAR
CELL AND ITS CURRENT-VOLTAGE
CHARACTERISTICS
Dong-Ho Kim
Korea Institute of Materials Science
531 Changwondaero, Changwon, Gyeongnam 641-831,
Korea
[email protected]
Introduction
† All-Si tandem solar cell
„ Inexpensive Si thin-film technology in combination
with high efficiency multi-bandgap approach.
„ Si QD superlattices are used as the higher bandgap
cells in a tandem stack
Device fabrications
† Si QD layers
„ SRO(4nm)/SiO2(2nm)
„ High T annealing
† Interdigitated structure
„ Photolitho and RIE
„ Al electrodes
E.-C. Cho, et.al, Nanotechnology 19, 245201 (2008).
Photovoltaic behaviors
JD: dark IV
J: light IV (AM1.5G spectrum, 25oC)
superposition approximation
(J(V) = JD(V) − Jsc) does not
hold
†
†
PV characteristic properties of a prototype cell
„ Effective area : 4.7 mm2
„ Voc = 394 mV, Jsc = 62 µA/cm2
Voltage–dependent photocurrent collection
„ Our Si QD layers in dielectric matrix have lots of defects
„ diffusion length would be very, very short
Current-Voltage characterization
J D (V) = J 0 [exp(q/nkT× Vj ) - 1] + Vj /R sh
where, Vj =V−J×Rs
1000
dV/dJ (Ω -cm2)
† Applying a diode model to
dark IV data
800
y = 7.640E-02x + 9.807E+01
2
R = 9.999E-01
600
400
200
0
Determination of parameters
† n, J0, Rs, Rsh
† Experimental and fitted dark
I-V curves
0.E+00
(a)
5.E+03
J (experimental)
J (fitted)
1.E-03
1.E-04
1.E-05
1.E-06
Jshunt
Jdiode
1.E-07
0
(b)
1.E+04
1/J (cm2/A)
1.E-02
J (A/cm2)
„
0.2
0.4
0.6
(V)
0.8
1
Current-Voltage characterization
† In reverse bias
(V)
This poor rectifying behaviour
of Si QD pn-junction is due to
the inter-diffusion of dopants
0.E+00
-1
-0.8 -0.6 -0.4 -0.2
-1.E-05
J shunt
JD (experimental)
-2.E-05
(c)
„
J L (A/cm2)
1.5E-04
Tunneling probabilities of
photogenerated carriers in QD
increase with electric field
Conduction mechanism in QD
materials is still complex issue
0.2
-3.E-05
† Photocurrent JL(V)=JD(V)-J(V)
„
0
J (A/cm2)
„
1.E-05
1.0E-04
5.0E-05
(V)
-1
(d)
0.0E+00
-0.8 -0.6 -0.4 -0.2
-5.0E-05
0
0.2 0.4 0.6
Concluding remarks
†
A single junction Si QD solar cell was fabricated and its
photovoltaic properties were examined.
†
The prototype device is promising towards the realization of
all-silicon tandem solar cells based on Si QD materials
†
For practical usage as a top cell in tandem device,
Voc should be increased above that of the standard cystalline
Si solar cells (>700 mV) and the current be improved in orders
of magnitude
†
Acknowledgements
„
„
„
Thank 3rd Gen members in Photovoltaics Centre of Excellence in
Univ. New South Wales (AU)
Korea Research Foundation Grant funded by the Korean
Government (MOEHRD) (KRF-2007-611- D00015).
Korea Nano Technology Research Association