FABRICATION OF SI QUANTUM-DOT SOLAR CELL AND ITS CURRENT-VOLTAGE - - PowerPoint PPT Presentation

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 dhkim2@kims.re.kr 6th U.S.-Korea Forums on Nanotechnology April 29 2009

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

• 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

superposition approximation (J(V) = JD(V) − Jsc) does not hold JD: dark IV J: light IV (AM1.5G spectrum, 25oC)

Current-Voltage characterization

• Applying a diode model to

dark IV data

• Determination of parameters
• n, J0, Rs, Rsh
• Experimental and fitted dark

I-V curves

y = 7.640E-02x + 9.807E+01 R2 = 9.999E-01 200 400 600 800 1000 0.E+00 5.E+03 1.E+04

1/J (cm2/A) dV/dJ (Ω-cm2)

(a)

1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02

0.2 0.4 0.6 0.8 1

(V) J (A/cm2)

J (experimental) J (fitted)

Jshunt Jdiode

(b)

sh j j D

/R V 1]

• )

V [exp(q/nkT J (V) J + × =

where, Vj =V−J×Rs

Current-Voltage characterization

• 3.E-05
• 2.E-05
• 1.E-05

0.E+00 1.E-05

• 1
• 0.8
• 0.6
• 0.4
• 0.2

0.2

(V) J (A/cm2)

JD (experimental) Jshunt

(c)

• 5.0E-05

0.0E+00 5.0E-05 1.0E-04 1.5E-04

• 1
• 0.8 -0.6 -0.4 -0.2

0.2 0.4 0.6

(V) JL (A/cm2)

(d)

• In reverse bias
• This poor rectifying behaviour
• f Si QD pn-junction is due to

the inter-diffusion of dopants

• Photocurrent JL(V)=JD(V)-J(V)
• Tunneling probabilities of

photogenerated carriers in QD increase with electric field

• Conduction mechanism in QD

materials is still complex issue

Concluding remarks

• 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
• 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

• f magnitude