由於銅鋅錯位導致開路電壓無法上升的問題，使得效率超過12.6%的
地表多豐CZTSSe(銅鋅錫硫硒)太陽能電池是非常困難的。藉由其他地
表富有的元素且必須有更⼤的原⼦半徑來取代鋅或銅元素以利克服錯
位的問題，並更進⼀步提升開路電壓。在本研究中，我們以鋇取代鋅，
使之形成三⽅晶系的CBTSSe(銅鋇錫硫硒)太陽能電池，並且提出⼀
種簡單且製程成本低的非真空噴霧裂解製程來製備銅鋇錫硫硒太陽能
電池。
然⽽利⽤非真空⽔溶液製程製備CBTSSe的前驅層中會有不均勻性的
問題，肇因於鋇元素和氧元素具有親和⼒並且氯元素會抑制CBTSSe
相⽣成，我們改良噴霧熱裂解時的基板溫度以及在後續增加額外的烘
烤以克服上述等問題，在最後，我們成功使⽤非真空製成製備出效率
達到0.6%的CBTSSe太陽能電池。

Reaching efficiency more than 12.6% in earth-abundant CZTSSe(Copper Zinc
Tin Sulpho-selenide) solar cells is very challenging as Copper-Zinc disorder remains
the biggest barrier in reaching higher open-circuit voltage. Replacing either Zinc or
Copper by another earth-abundant element bigger in size can solve the disordering
issue and subsequently reach a higher open-circuit voltage. In this work, we
replace Zinc with Barium and form a promising trigonal structure earth-abundant
Cu2BaSn(S,Se)4 (CBTSSe) solar cells. Our work presents a simple and inexpensive
solution-based approach to fabricate earth-abundant Copper Barium Tin Sulphoselenide(CBTSSe) solar cells.
To fabricate CBTSSe solar cells by non-vacuum and solution-based process is
challenging as non-uniformity in precursor due to barium affinity towards oxygen
and chlorine refrain the phase formation. To solve this problem we devised a spray
and bake method to form for the first time 0.6% efficient CBTSSe solar cells by
water-based spray pyrolysis process.

Table of Content
Table of Content 4
List of figures 6
List of tables 8
Chapter 1 : Background and motivation 9
Distribution of thesis 15
Chapter 2 : Solar cells 16
2.1 - History of solar cells 16
2.2 - History of thin film solar cells 16
2.3 - Physics of solar cells 17
2.4 - J ( Current density) - V (voltage) curve 18
2.5.1 - Short circuit current density (Jsc) 19
2.5.2 - Open-circuit voltage (Voc) 20
2.5.3 Fill factor (FF) 21
2.5.4 Efficiency 21
2.5.5 - Series resistance (Rs) 22
2.5.6 - Shunt resistance (Rsh) 22
2.5 - Recombination mechanism 23
2.5.1 - Band to Band recombination 24
2.5.1 - Auger recombination 24
2.5.3 - Recombination through intermediate level or a defect state 24
Chapter 3 : CBTSSe solar cells 26
3.1 - Crystal structure 26
3.2 - Defect system 27
3.3 - Phase region 30
3.4 - Overview on the fabrication of CBTSSe thin film 32
3.4.1 - Vacuum processes 32
3.4.1.1 - Co-Sputtering 32
3.4.2 - Non-vacuum processes 32
3.4.2.1 - Chemical spray pyrolysis 33
3.5 - Characterizations 33
3.5.1 - Material analysis 33
3.5.1.1 - Scanning Electron Microscopy (SEM) 33
3.5.1.2 - Energy Dispersive X-ray Spectroscopy (EDX/EDS) 34
3.5.1.3 - Raman Spectroscopy 34
!4
3.5.1.4 - X-ray Diffraction (XRD) 34
3.5.1.5 - Photoluminescence(PL) Spectroscopy 35
3.5.2 - Electrical characterisation 36
3.5.2.1 - Current-Voltage (IV) measurement 36
3.5.2.2 - Capacitance-Voltage (CV) measurement 36
3.5.2.3 - External quantum efficiency (EQE) 37
Chapter 4 : General experimental procedure 38
5.1.1 - Molybdenum (Mo) back contact 39
5.1.2 - CBTSSe absorber 39
5.1.2.1 - Preparation of the solution 40
5.1.2.2 - Fabrication of CBTSSe films 40
5.1.3 - Cadmium Sulphide (CdS) buffer layer 41
5.1.4- Window layer 42
5.1.5 - Silver grid 42
5.1.6 - Characterizations 42
Chapter 5 : Results and discussion 43
5.1 - Phase formation 43
5.1.1 - Overcoming a non-uniform precursor film 43
5.1.2 - Effects of selenium during sulphurisation 50
5.2 - Device performance and characterisation 54
Chapter 6 : Conclusion and outlooks 59
6.1 - Challenges 59
6.2 - Summary 60
6.3 - Future prospects for CBTS solar cells and non-vacuum process 61
References 62

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