Development of cadmium selenide as an absorber layer for tandem

89 Pages·2015·1.16 MB·English

by  Sathyaharish Jeedigunta

University of South Florida
Scholar Commons
Graduate Theses and Dissertations Graduate School
3-26-2004
Development Of Cadmium Selenide As An
Absorber Layer For Tandem Solar Cells
Sathyaharish Jeedigunta
University of South Florida
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Jeedigunta, Sathyaharish, "Development Of Cadmium Selenide As An Absorber Layer For Tandem Solar Cells" (2004).Graduate
Theses and Dissertations.
https://scholarcommons.usf.edu/etd/1093
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Development Of Cadmium Selenide As An Absorber Layer For Tandem Solar Cells

by

Sathyaharish Jeedigunta

A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Science in Electrical Engineering
Department of Electrical Engineering
College of Engineering
University of South Florida

Major Professor: Don Morel, Ph.D.
Christos Ferekides, Ph.D.
Y.L.Chiou, Ph.D

Date of Approval:
March 26, 2004

Keywords: css, fill factor, trasmission, substrate temperature

© Copyright 2004 , Sathyaharish Jeedigunta
Dedication

To my parents and brother.
Acknowledgments

I would like to convey my deepest appreciation to my major professor, Dr.Don
Morel for giving me an opportunity to be a member of his research group. His excellent
guidance was of great help during my thesis work. I am very much thankful for his
support and guidance. I would also like to thank Dr.Chris Ferekides and Dr.Y.L.Chiou
for their assistance.

I am more than happy to work with my fellow researchers and express my thanks
to all of them who have helped me in every stage of my work. My special thanks to
Prasanna Mahawela, Harish Sankarnarayanan, Sridevi Vakkalanka, Shirish Pethe,
Venkatesh and Madhavi. I am thankful for the encouragement provided by Vijay, Raghu
and other friends.

I am thankful to god who has given me his support and blessings. I am very much
indebted to my parents and my brother for their encouragement.
Table of Contents

List of Tables v
List of Figures vi
List of Abbreviations ix
Abstract xii

Chapter 1 Introduction 1
1.1 Introduction 1
1.2 Economics of Photovoltaics 4
1.3 Outline 6

Chapter 2 Background 7
2.1 Photovoltaics 7
2.2 Benefits of Photovoltaics (PV) 7
2.3 Photovoltaic Effect 8
2.4 History 8
2.4.1 Problems with Amorphous Silicon 9
2.4.2 GaAs- an Interesting Material 9
2.4.3 Thin Film Polycrystalline Solar Cells 9
i
2.4.4 Advantages of Thin Film Polycrystalline Solar Cells 10
2.4.5 Disadvantages of Thin Film Polycrystalline Solar Cells 10
2.5 Structure of Solar Cell 11
2.6 Principle of Operation of Solar Cell 12
2.7 Typical I-V Curve 13
2.7.1 Effect of Series and Shunt Resistance 14
2.7.1.1 Effect of Series Resistance 15
2.7.1.2 Effect of Shunt Resistance 15
2.8 Requirements of the Materials used in Solar Cells 16
2.8.1 Back Contact 16
2.8.2 Absorber Layer 17
2.8.3 Window Layer 17
2.8.4 Front Contact 18

Chapter 3 Literature Review 19

Chapter 4 Device Structure and Fabrication 32
4.1 Tandem Cell Structure 32
4.2 Structure of a CdSe Based Top Cell 34
4.2.1 Substrate 34
4.2.1.1 Cleaning Procedure 34
4.2.2 Back Contact 35
4.2.2.1 Deposition of SnO : F 36
2
ii
4.2.2.2 AZO as a Back Contact 36
4.2.2.3 Structure of Cell with AZO at the Back Contact 37
4.2.2.4 Deposition Procedure for AZO 38
4.2.2.5 Transmission of AZO 38
4.2.3 Absorber Layer 39
4.2.3.1 Properties of CdSe 41
4.2.3.2 Preparation of the CdSe Source 41
4.2.3.3 Deposition Procedure for CdSe 41
4.2.3.4 Parameters 42
4.2.3.5 Transmission of CdSe 43
4.2.3.6 Experiments Performed on the Absorber Layer 43
4.2.4 Window Layer 44
4.2.4.1 Properties of ZnSe 45
4.2.4.2 Deposition Procedure for ZnSe 45
4.2.4.3 Evaporation System 46
4.2.4.4 Transmission of ZnSe 47
4.2.5 Front Contact 47
4.2.5.1 Transmission of Copper 48
4.3 Deposition of Cadmium Sulphide 48
4.3.1 Transmission of CdS 50

4.3.2 Structure of Cell with CdSe on CdS/SnO : F 51
2

iii
Chapter 5 Results and Discussions 52
5.1 Results 52
5.1.1 AZO as a Back Contact 52
5.1.2 CdS on SnO : F at the Back Contact 54
2
5.1.3 Absorber Layer at Higher Substrate Temperatures 57
5.1.4 Effect of Time on Device Performance 63

Chapter 6 Conclusions 66

References 70

iv
List of Tables

Table 3.1 Device Parameters 24
Table 4.1 Properties of CdSe 41
Table 4.2 Properties of ZnSe 45
Table 5.1 Device Parameters for Devices with AZO as a Back Contact 52
Table 5.2 Device Parameters for Devices with CdS on SnO : F at Back Contact 55
2
Table 5.3 Effect of Substrate Temperature on Device Performance with
200 Å ZnSe 58

Table 5.4 Effect of Substrate Temperature on Device Performance with
220 Å ZnSe 59

Table 5.5 Effect of Substrate Temperature on Device Performance with
180 Å ZnSe 61

Table 5.6 Effect of Time on Device Performance 63

v
List of Figures

Fig 1.1 Module World Market Growth 4
Fig 2.1 Substrate Structure 11
Fig 2.2 Superstrate Structure 11
Fig 2.3(a) Equivalent circuit of an ideal solar cell (b) Equivalent circuit of
solar cell with series and shunt resistances 12

Fig 2.4 Typical I-V Curve 14
Fig 2.5 Effect of Series Resistance 15
Fig 2.6 Effect of Shunt Resistance 16
Fig 3.1 XRD Pattern of CdSe Film Deposited from an Electrolyte
Containing CdCl 20
2

Fig 3.2 XRD Pattern of CdSe Film Deposited from an Electrolyte
Containing CdSO at a) T=18°C b) T=75°C 21
4

Fig 3.3 I-V Curve 22
Fig 3.4 Photo-current Action Spectra for Different Electrodes
a) OTE/SnO b) OTE/CdSe c) OTE/SnO /CdSe 23
2 2

Fig 3.5 I-V Curve of CdSe and CdZnSe 25
Fig 3.6 a) AFM results for T =300 K b) AFM results for T =400 K 26
s s
Fig 3.7 I-V characteristics of a) undoped- PMeT/CBD CdSe
b) doped - PMeT/CBD CdSe
c) doped - PMeT/CBD CdSe (in presence of Silicon Tungstic Acid) 28

Fig 3.8 Variation of Band gap Vs Deposition Temperature 29
Fig3.9 Variation of Resistivity Vs Deposition Temperature 30
Fig 3.10 J -V characteristics of CdSe thin films with temperature as variable
a) with bias voltage < 0.6V b) with bias voltage > 0.6V 31

vi