Nanopatterned ZnCdTe Solar Cells · 2017. 9. 5. · NanoMaterials Integration Laboratory . Nanopatterned ZnCdTe Solar Cells . David Zubia . April 4, 2013 . Energy Efficient Electronics

NanoMaterials Integration Laboratory

Nanopatterned ZnCdTe Solar Cells

David Zubia

April 4, 2013

Energy Efficient Electronics Science

For Internal E3S Use Only. These Slides May Contain Prepublication Data and/or Confidential Information.


El Paso Del Norte Safest city in US for 3rd straight year



UTEP Doctoral Enrollment Growth 17 doctoral programs

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Total Yearly Doctoral Enrollment

Teaching, Learning and Culture (36)

Computer Engineering (16)

Computational Science (16)

Chemistry (22)

Computer Sciences (24)

Interdisciplinary Health Sciences (32)

Eng. Rhetoric and Composition (22)

International Business (25)

Civil Engineering (11)

History (34)

Biological Sciences (49)

Education Leadership & Admin. (53)

Environmental Science & Engineering (41)

Psychology (35)

Materials Science and Engineering (20)

Electrical and Computer Engineering (12)

Geological Sciences (12)



Growth in Research Expenditures

7.8 9.6 10.4

12.9 12.9 13.8 13.7 17.3

14.8

28 29.6 31.1 32.9

36.4 36.9

45.7 46.4

50.6

56.5

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Electrical Engineering Enrollment UTEP: 22,000 students Engineering: 3,000 students

330

377 411

440 416 408 408

440

389 393 409 370

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82 94 97 94

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F'01 F'02 F'03 F'04 F'05 F'06 F'07 F'08 F'09 F'10 F'11 F'12

UTEP ECE Enrollment

Undergraduate Masters PhD



UTEP Enrollment: Student Race/Ethnicity Trends

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2012 Recognition by Washington Monthly



Faculty in the Area David Zubia (electrical engineering)

Memristors Patterned solar cells Nanoscale crystal growth

Eric MacDonald (electrical engineering) Rad-Hard CMOS design

Jose Mireles (electrical engineering, UACJ-CICTA)

MEMS devices and packaging

John McClure (materials science) Solar cells ZnCdTe layers using CSS

Stella Quinones (electrical engineering)

CdTe single crystal growth using CSS Electrode-less plating

Joseph Pierluissi (electrical engineering) Memristors Electromagnetics

New Hire (fall 2013)



Facilities

Science and Engineering Neighborhood

Campus Transformation



NanoFabrication Facility ~$5.0M investment

6,000 SF total, 2,500 SF clean

Class-100 & Class-1000

23 Major pieces of equipment

Teaching

Research

BS, MS, Ph. D. For Internal E3S Use Only. These Slides May Contain Prepublication Data and/or Confidential Information.


Research Lines Total Funding ~$5.3M

SnO2-based Memristors CdTe-based Solar Cells NSF, DOE, NINE

SiO2

~100 nmZnxCd(1-x)Te

Cadmium sulfide substrate

CdTe

Memristor Array Solar Cell Array



Patterned Solar Cells

V. G. Karpov, et. al., Phys. Rev. B 69 (2004) 045325

Sample "b5" - CuTe-doped Graphite Contacts

-30

-20

-10

0

10

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30

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50

60

-1.5 -1 -0.5 0 0.5 1 1.5

Voltage (V)

Cur

rent

Den

sity

(mA

/cm

2)

Cross-sectional view



Graded Bandgap Nanoarrays

Pseudomorphic growth of graded ZnxCd(1-x) in nanoscale windows of ~100nm

SiO2

~100 nmZnxCd(1-x)Te

Cadmium sulfide substrate

CdTe

CdSBandgap 2.50eVL.P. 0.582nm

ZnTeBandgap 2.39eVL.P. 0.582nm

CdTeBandgap 1.44eVL.P. 0.648nm

c

Combined 3D strain relief (grid) and bandgap variation (color).



Graded Bandgap Solar Cells

Electric fields act on electrons and holes

Increase collection efficiency

Absorption over wider spectrum Improved lattice matching at CdS/ZnTe interface compared to CdS/CdTe.

Decreases mismatch: 10% to 3% Pseudo-morphic growth possible

Reduces SRH recombination Increases Voc

CdS/ZnTe Band-offset enhances electron-hole charge separation

Increases fill-factor

Excellent ZnTe Ohmic contact Reduce series resistance

Zero Valence-band offset between CdTe and ZnTe

Holes pass freely from CdTe to ZnTe

p-CdTe

p-ZnxCd1-xTe

p-ZnxCd1-xTe n-CdS

2.4 eV

1.5 eV 2.3 eV

Ef EC

EV metal



Experimental/Computational Collaboration



16

BOP-based MD

• Emerges to be a new,

powerful method to

study thin film growth

• Captures the crystalline

growth of

stoichiometric films

(Cd/Te = 1) under non-

stoichiometric, random

vapor fluxes

• Reveals misfit

dislocation formation

J. J. Chavez, D. K. Ward, B. M. Wong, F. P. Doty, J. L. Cruz-Campa, G. N. Nielson, V. P. Gupta, D. Zubia,

J. McClure, and X. W. Zhou, Defect formation dynamics during CdTe overlayer growth, Unpublished

Crystal Growth Simulation Xiaowang Zhou, Sandia National Labs



17

• BOP allows system

energy as a function of

dislocation spacing to be

derived

• Minimization of system

energy with respect to

dislocation spacing

leads to an equilibrium

spacing around 3.8 nm,

matching remarkably

well with experiments

J. J. Chavez, D. K. Ward, B. M. Wong, F. P. Doty, J. L. Cruz-Campa, G. N. Nielson, V. P. Gupta, D. Zubia,

J. McClure, and X. W. Zhou, Defect formation dynamics during CdTe overlayer growth, Unpublished

Validation of Crystal Growth Simulation Xiaowang Zhou, Sandia National Labs



CdTe/CdS(0001) growth is simulated Predicted defects are validated by experiments

18 Exp. from Y. Yan, R. G. Dhere, K. M. Jones, and M. M. Al-Jassim, J. Appl. Phys. 89, 5844

(2001).

Simulation from Xiaowang Zhou, Sandia National Labs



Selective-Area Crystal Growth

Tilted 60o

Prior to

Deposition

Tsub = 350oC

Tso = 530oC

Tsub = 450oC

Tso = 530oC

P = 4-5 Torr

t = 15 min

Stella Quinones, UTEP For Internal E3S Use Only. These Slides May Contain Prepublication Data and/or Confidential Information.


SEM of 2 µm vs. 300 nm patterning

2 𝝁m

b) 300 nm feature

20 𝝁m

a) 2 𝝁m feature

5 𝝁m 500 nm

400 nm 1 𝝁m

d) 300 nm feature c) 2 𝝁m feature

f) 300 nm feature e) 2 𝝁m feature



Diminishing the window size reduces the number of grains grown per window

21

Cross-section SEM View 1 𝝁m window size 130 nm window size

1 𝝁m 1 𝝁m Single crystal CdS

SiO2

SiO2

CdTe CdTe

Single crystal CdS

Multiple CdTe grains

Single CdTe seed?

21

Using a precision cutting tool ( Focused Ion beam or FIB)

and a SEM, we were able to see the difference in growth

using different window sizes of the nanopattern. Smaller

sizes are preferred For Internal E3S Use Only. These Slides May Contain Prepublication Data and/or Confidential Information.


EBSD indicates single domain in windows

Not patterned

22

50 µm

50 µm

2 µm

50 µm

50 µm

2 µm

(a) (b)

(c)

(e) (f)

(d)

2 µm pattern

300 nm pattern



Nanoprobing of Patterned Solar Cells



Topology images and electric current maps can be obtained using conductive scanning AFM in contact mode

Area A

Area B

Area C

AFM Current Map

SiO2

CdTe

CdTe SiO2

AFM Voltage amplitude

image SEM Image AFM deflection

image

Shaved

Unshaved 24



IV data using conductive scanning AFM

IV on CdTe island IV on SiO2

- Zoom-in option in AFM system can be used to analyze individual CdTe islands. - Bright color denotes an area with high electric current (center image)

CdTe

SiO2



TEM and FFT Analysis of CdTe/CdS Interface

d-spacing Theory

h k l CdTe (Å) CdS (Å) mismatch %

0 1 0 3.97 3.58 9.82

0 1 1 3.51 3.16 9.97

0 1 2 2.72 2.46 9.56

0 0 2 3.74 3.37 9.89

d-spacing Sample (near junction)


0 1 0 3.45 3.03 12.17

0 1 1 3.03 2.7 10.89

0 1 2 2.27 2.04 10.13

0 0 2 3.13 2.78 11.18

0

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4

6

8

10

12

14

0 1 2 3 4 5

Mis

mat

ch (

%)

Orientation

CdS/CdTe d-spacing mismatch (sample)

Theory

Near junction

010 011 012 002 9.81% Average

TEM image (real space) FFT (reciprocal space)

CdS

CdTe

CdS

CdTe

11.9% Average

TEM Image

Artificial atoms

Image calibration

Area of Interest for FFT

010

011

012 002

000



FFT Analysis of Simulated CdTe/CdS Growth

d-spacing Theory


0 1 0 3.97 3.58 9.82

0 1 1 3.51 3.16 9.97

0 1 2 2.72 2.46 9.56

0 0 2 3.74 3.37 9.89

d-spacing simulated junction (20nm-thick)


0 1 0 1.34 1.2 10.45

0 1 1 1.14 1.07 6.14

0 1 2 0.9 0.82 8.89

0 0 2 1.26 1.14 9.52

0

2

4

6

8

10

12

0 1 2 3 4 5

Mis

mat

ch (

%)

Orientation

CdS/CdTe d-spacing mismatch (simulation)

Theory

Simulation

010

011

012 002

9.81% Average

CdS

CdTe

211.32 Å

TEM image (real space) FFT (reciprocal space)

Note: CdS substrate is fixed

8.75% Average

010

011

012 002

000



Unique Ternary Depositor



Deposition of ZnCdTe ternary

-Same parameters used

for both samples.

Differences during

depostion:

-CML2 deposition had

less source temp

variation

-Faster cooldown rate

Peaks shifted due to low

grazing angle used on

machine

d-value 3.64

Ternary composition

ZnTe source temp:

675

CdTe source temp:

560

Substrate temp:

400

Ternary composition

found and very clear

specifically in CML1

sample

d-value 2.25

Ternary composition



Acknowledgements Jose Cruz-Campa, Sandia National Labs Xiaowang Zhou, Sandia National Labs Doug Pete, Center for Integrated Nanotechnologies John McClure, UTEP Stella Quinones, UTEP Brandon Aguirre, UTEP Jose Chavez, UTEP Damian Marrufo, UTEP Abraham Alvarez, UTEP Francisco Alvarado, UTEP



NanoMIL Collaborators Universities

National Labs

Funding

Companies



Thank you!


Documents

Nanopatterned ZnCdTe Solar Cells · 2017. 9. 5. · NanoMaterials Integration Laboratory . Nanopatterned ZnCdTe Solar Cells . David Zubia . April 4, 2013 . Energy Efficient Electronics