project3.ppt

7/28/2019 project3.ppt

1/46

Nanotechnology Application for

Solar Cells: Using Quantum Dotsto Modify Absorption Properties

Prepared by

James Fodor

Kwok Mak

Viet Huynh


2/46

Introduction

How Classical Solar Cells Operate Absorption Coefficient ()

Definition and Relevance of Physical Techniques for Measuring

Light Absorption of Quantum Dot Layers Reasons for Interest Into Quantum Dot Light Absorption Definition of a Quantum Dot Formula for Light Absorption of a Quantum Dot Comparison of versus Energy for Bulk Material and Quantum Dot

Researchers working on Light Absorption of Quantum Dots Dr. Sheila Baily Dr. Ryne Raffaelle

Problem Statement Determining the most optically absorbent

semiconductor material Problem Solution

Explanation of Theory Results


3/46

Introduction


Definition and Relevance of

Physical Techniques for Measuring

Light Absorption of Quantum Dot Layers Reasons for Interest Into Quantum Dot Light Absorption

Definition of a Quantum Dot Formula for Light Absorption of a Quantum Dot

Comparison of versus Energy for Bulk Material and Quantum Dot

Researchers working on Light Absorption of Quantum Dots Dr. Ryne Raffaelle Dr. Sheila Baily

Problem Statement Determining the most optically absorbentsemiconductor material

Problem Solution Explanation of Thoery Results


4/46

How Classical Solar Cells Operate1,2


5/46



6/46



7/46



8/46



9/46



10/46



11/46



12/46

Introduction









Problem Solution Explanation of Thoery Results


13/46

Absorption Coefficient

Definition and Relevance of3

Definition of Absorption Coefficient

A measure of the rate in decrease ofelectromagnetic radiation (as light) as

it passes through a given substance;the fraction of incident radiant energyabsorbed per unit mass or thickness ofan absorber.


14/46



Unit of Absorption Coefficient

The units of are per length (cm-1)


15/46



Unit of Absorption Coefficient

The units of are per length (cm-1)


16/46



Absorption Versus Transmission

Transmission (t): a measure of conduction of

radiant energy through a medium, often

expressed as a percentage of energypassing through an element or system

relative to the amount that entered.


17/46









18/46








0 0.2 0.4 0.6 0.8

2

4

6

8

1010

0

t( )

10 t


19/46


Physical Techniques for Measuring 5,6

Optical Transmission Measurement

t Measured transmission

l Sample thickness

R - Reflectance

t1 R( )2 e

l

1 R2

e2 l


20/46

Introduction




Light Absorption of Quantum Dot Layers Why We Are Interested



Researchers working on Nano-coating Dr. Ryne Raffaelle Dr. Sheila Baily


Problem Solution Explanation of Theory Results


21/46

Light Absorption of Quantum Dots

Why We Are Interested7,8,13

These structures have greatpotential for optoelectronicapplications, one of which may be

solar cells Standard solar cells have a

theoretical upper conversion rate of33%, the theoretical limit on the

conversion of sunlight to electricityis 67%


22/46


Definition of a Quantum Dot9

Quantum Dot


23/46



Quantum Dot Layer


24/46



Quantum Dot Layer


25/46


Formula7

_

Vav = Average Dot Volume

pfi= 2d momentum matrix element

a = polarization of light

N() = density of states


26/46


Formula12

Transmission for Quantum dots.

For transmission through n planes of dots, eachhaving the same dot density N and each dotexperiencing the same optical field amplitude, the

transmission fraction is: Tn=(1-N)

n (1-nN) ; (N


27/46


Comparison of versus Energy for Bulk

Material and Quantum Dot9

Li ht Ab ti f Q t D t


28/46



Material and Quantum Dot



29/46



Material and Quantum Dot



30/46






31/46





32/46

Introduction











33/46

Researchers Working on Light

Absorption of Quantum Dot Layers

Dr. Sheila Bailey

Using quantum dots in a solar cell to create anintermediate band

IEEE Photovoltaic Specialist Conference (PVSC)Executive Committee since 1987

http://www.grc.nasa.gov/WWW/RT2001/5000/5410bailey1.html


34/46

Researchers Working on Light

Absorption of Quantum Dot Layers11

Dr. Ryne Raffaelle

Rochester Institute of Technology

NanoPower Laboratories

Organic and Plastic Solar Cells Combinedwith Quantum Dot Layers

http://www.physlink.com/News/Images/QDots1_lg.jpg


35/46

Introduction











36/46

Problem Solution

Explanation of theory

z = propagation direction

nr = refractive index

omega = frequency

alpha = absorption coefficient

Laws of Conservation

Energy

Momentum

)2

exp()](exp[z

tc

niEE ro

Figures based on Singhtextbook

Photon Absorption

Photon Emission

)(|)*(|1 2

2

2

cvif

oro

Npa

mcn

e

32

2/12/3* )()(2)(

gr

cv

EmN

cvif ppa22

32|)*(

eVm

p

o

cv

24~20

2


37/46

Problem Statement Determining the most

optically absorbent semiconductor bulk

Consider InP and GaAs as being the availablesemiconductors to create a solar cell. This solarcell will be a hybrid, consisting of a traditional

solar cell created with either InP or GaAs, andcoating layers of quantum dots of either InP orGaAs. If maximizing absorption is the onlycriteria for designing the solar cell, which materialshould be used for the bulk? Which should beused for the quantum dot layers? Assume the

density of states for quantum dot layers of bothmaterials is equal and occurs at the same point, E= .1eV, and that the polarization-momentumproduct sum is the same in both cases.


38/46

Problem Statement Determining the most

optically absorbent semiconductor bulk

Absorption coefficient of InP andGaAs

Required constants by material

14

Material ElectronMass(mo)

Hole Mass(mo)

Calculatedreducedmass (mo)

Eg(eV)

LatticeConstant(A)

Refractiveindex(nr)

Gallium

Arsenide,GaAs

0.067 mhh* = 0.45 mr

*

=0.058

1.5 5.65 3.65

IndiumPhosphide,InP

0.073 mhh* = 0.45 mr

*

=0.0581.34 5.87 3


39/46

Introduction











40/46

Problem Solution

Results: GaAs Bulk


41/46

Problem Solution

Results: InP Bulk


42/46

Problem Solution

Results


43/46

Problem Solution

Results: GaAs Quantum Dot Layer


44/46

Problem Solution

Results: InP Quantum Dot Layer


45/46

Conclusion


Definition and Relevance of Physical Techniques for Measuring

Light Absorption of Quantum Dots Reasons for Interest Into Quantum Dot Light Absorption

Definition of a Quantum Dot Formula for Light Absorption of a Quantum Dot Comparison of versus Energy for Bulk Material and Quantum Dot


Problem Statement Determining the most optically absorbent

semiconductor material Problem Solution

Explanation of Theory Results


46/46

References

1. Seale, Eric. Solar Cells: Shedding a Little Light on Photovoltaics. 28, Feb. 2002. Solarbotics.. Accessed03/20/2005.

2. Pierret, Robert F. Semiconductor Device Fundaments. Addison Wesley Longman, 1996. pp 198-205.3. Anonymous. Absorption Coefficient. Undated. LaborLawTalk.

. Accessed 04/01/2005.4. Anonymous. Transmission (T). Undated. Photonics Directory.

. Accessed 04/01/2005.

5. Augustine, G. Jokerst, N.M. Rohatgi, A.Absorption measurements of doped thin film InP for solar

cell modeling. IEEE:Indium Phosphide and Related Materials, 1992., Fourth International Conferenceon. 21-24 April 1992.6. Gerber, D.S. Maracas, G.N. A simple method for extraction of multiple quantum well absorption

coefficient from reflectance and transmittance measurements. Quantum Electronics, IEEE Journal of.Volume: 29 , Issue: 10. Oct. 1993.

7. Kochman, B; Singh, J; et al. Absorption, Carrier Lifetime, and Gain in InAs-GaAs Quantum DotInfrared Photodetectors. IEEE Journal of Quantum Electronics. Volume 39, Number 3. March 2003.

8. Anonymous. Photovoltaics. Evident Technologies. Undated.. Accessed 04/14/2005.

9. Singh, J. Modern Physics for Engineers. John Wiley & Sons, Inc. 1999. pp 34, 156.10. Wu, Y. Singh, J. Polar Heterostructure for Multifunction Devices: Theoretical Studies. IEEE

Transaction on Electron Devices. VOL. 52, NO. 2, FEBRUARY 2005

11. Raffaelle, R. Profile of Ryne P. Raffaelle. RIT Department of Physics. Undated.. Accessed 04/10/2005.

12. Blood, P. On the Dimensionality of Optical Absorption, Gain, and Recombination in Quantum-Confined Structures. IEEE Journal of Quantum Electronics. Vol. 36, No. 3, March 2000.

13. D. Pan, E. Towne, and S. Kennerly. Strong normal-incident infrared absorption and photo-currentspectra from highly uniform (In,Ga)As/GaAs quantum dot structures. IEEE Electronic Letters. 14thMay 1998 Vol. 34 No. 10.

Date post:	03-Apr-2018
Category:	Documents
Upload:	binod-kumar
View:	216 times
Download:	0 times

project3.ppt

Documents