Cathodic Deposition of CdTe from Aqueous Electrolytes

and high-temperature growth techniques. The wide bandgap (E g = 2.42 eV) window material, CdS was mainly grown by chemical bath deposition (CBD) and narrow bandgap (E g = 1.45 eV) absorber material, CdTe was grown by over 14 different methods [1]. High efficiencies were achieved by the combination of CdS with CdTe layers grown by high temperature growth methods such as closed space sublimation (CSS) or close spaced vapour transport (CSVT) for a long period. Depending on the growth technique, material growth mechanisms, micro-structure and impurity inclusions are going to vary. Although there are a large number of publications reporting material characterisation, deep understanding is required on material issues such as defects and doping concentrations.The next area needing deeper understanding is the postgrowth chemical and heat treatment. The devices fabricated using as-made CdTe materials show poor device performance in the range ~(0-6)% depending on the growth technique used. However, from 1976 [2], the researchers were aware of the drastic improvement of the device performance after heat treatment around 450 °C in air, in the presence of CdCl 2 . This was known as "CdCl 2 treatment" and device efficiencies improved to mid-teens achieving good solar cell performance. Although there were tremendous efforts to explore the complexity of changes during this treatment, full understanding has not yet been achieved.The third main area of complexity comes from the CdTe/electrical back contact formation. It is essential to clean the CdTe surface after CdCl 2 treatment, and researchers were using different chemicals to clean the surface prior to metallisation. Various electrical contacts have been used to complete the devices and varying results have been reported in the literature [3]. Initial high efficiency, reproducibility and yield, stability and lifetime are main features of fully fabricated devices to establish. Some of these Abstract Thin film solar cells based on CdS/CdTe hetero-structure has shown a drastic improvement changing from 16.5 to 22.1% efficiency during a short period of time from ~2013 to ~2016. This has happened in the industrial environment and the open research in this field has stagnated over a period of two decades prior to ~2013. Most of the issues of this hetero-structure were not clear to the photovoltaic (PV) community and research efforts should be directed to unravel its complex nature. Issues related to materials, post-growth treatment, chemical etching prior to metallisation and associated device physics are the main areas needing deeper understanding in order to further develop this device. After a comprehensive research programme in both academia and in industry on these materials, surfaces and interfaces and fully fabricated devices over a period of over three decades by the main author, the current knowledge as understood today, on all above mentioned complex issues are presented in this paper. Full understanding of this structure will enable PV developers to further improve the ...

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“…Some of the most popular methods for growing CdTe layer are CSS [16], CSVT [17], sputtering [18] and electrodeposition [19,20].…”

Section: Materials Issuesmentioning

confidence: 99%

Unravelling complex nature of CdS/CdTe based thin film solar cells

Dharmadasa

Ojo

2017

J Mater Sci: Mater Electron

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“…It should be noted that the 85 °C bath temperature used during the growth of CdTe layer was due to higher crystallinity achievable at higher growth temperature [7], but due to the aqueous solution utilised in this experiment, the growth temperature is limited. In this work, two-electrode configuration was utilised.…”

Section: Electrolytic Bath Preparationmentioning

confidence: 99%

Analysis of electrodeposited CdTe thin films grown using cadmium chloride precursor for applications in solar cells

Ojo

Dharmadasa

2017

J Mater Sci: Mater Electron

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“…Various techniques have been reported for preparation of CdTe thin films such as physical vapour deposition (PVD) [2], RF sputtering [3], spray pyrolysis [4], close-space sublimation (CSS) [5,6] and electrodeposition (ED) [7][8][9][10][11][12]. Electrodeposition is an attractive technique for the preparation of CdTe because of its low-cost, simplicity, scalability, manufacturability and ability to obtain p-, i-or n-type materials by controlling the cathodic voltage during electrodeposition [12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Electro-Plating and Characterisation of CdTe Thin Films Using CdCl2 as the Cadmium Source

et al. 2015

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Cadmium telluride (CdTe) thin films have been successfully prepared from an aqueous electrolyte bath containing cadmium chloride (CdCl2)·H2O and tellurium dioxide (TeO2) using an electrodeposition technique. The structural, electrical, morphological and optical properties of these thin films have been characterised using X-ray diffraction (XRD), Raman spectroscopy, optical profilometry, DC current-voltage (I-V) measurements, photoelectrochemical (PEC) cell measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-Vis spectrophotometry. It is observed that the best cathodic potential is 698 mV with respect to standard calomel electrode (SCE) in a three electrode system. Structural analysis using XRD shows polycrystalline crystal structure in the as-deposited CdTe thin films and the peaks intensity increase after CdCl2 treatment. PEC cell measurements show the possibility of growing p-, i-and n-type CdTe layers by varying the growth potential during electrodeposition. The electrical resistivity of the as-deposited layers are in the order of 10 10884(1.48-1.52) eV reduce to (1.45-1.49) eV after CdCl2 treatment. Full characterisation of this material is providing new information on crucial CdCl2 treatment of CdTe thin films due to its built-in CdCl2 treatment during the material growth. The work is progressing to fabricate solar cells with this material and compare with CdTe thin films grown by conventional sulphate precursors.

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Cathodic Deposition of CdTe from Aqueous Electrolytes

Cited by 475 publications

References 3 publications

Unravelling complex nature of CdS/CdTe based thin film solar cells

Unravelling complex nature of CdS/CdTe based thin film solar cells

Analysis of electrodeposited CdTe thin films grown using cadmium chloride precursor for applications in solar cells

Electro-Plating and Characterisation of CdTe Thin Films Using CdCl2 as the Cadmium Source

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