Influence of annealing in different chlorides on the photovoltaic parameters of CdS/CdTe solar cells

Potlog, Tamara; Ghimpu, Lidia; Gashin, P.; Pudov, A.O.; Nagle, Timothy J.; Sites, James R.

doi:10.1016/j.solmat.2003.08.007

Cited by 40 publications

(21 citation statements)

References 5 publications

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“…When V g is increased from 1.576 V, the n-type doping concentration increases along curve iC'. The observation of reported results in the literature indicates that the best solar cell efficiency for CdTe is produced when the doping concentration is in the range ~1.0 × 10 14 -5.0 × 10 15 cm −3 [3,[33][34][35].…”

Section: Summary Of Electrodeposition Of Cdte Resultsmentioning

confidence: 93%

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Fabrication of CdS/CdTe-Based Thin Film Solar Cells Using an Electrochemical Technique

et al. 2014

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Thin film solar cells based on cadmium telluride (CdTe) are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results from the literature with new results from a research programme based on electro-plated CdS and CdTe. A wide range of analytical techniques was used to investigate the materials and device structures. It has been experimentally found that n-, i-and p-type CdTe can be grown easily by electroplating. These material layers consist of nano-and micro-rod type or columnar type grains, growing normal to the substrate. Stoichiometric materials exhibit the highest crystallinity and resistivity, and layers grown closer to these conditions show n → p or OPEN ACCESSCoatings 2014, 4 381 p → n conversion upon heat treatment. The general trend of CdCl 2 treatment is to gradually change the CdTe material's n-type electrical property towards i-type or p-type conduction. This work also identifies a rapid structural transition of CdTe layer at 385 ± 5 °C and a slow structural transition at higher temperatures when annealed or grown at high temperature. The second transition occurs after 430 °C and requires more work to understand this gradual transition. This work also identifies the existence of two different solar cell configurations for CdS/CdTe which creates a complex situation. Finally, the paper presents the way forward with next generation CdTe-based solar cells utilising low-cost materials in their columnar nature in graded bandgap structures. These devices could absorb UV, visible and IR radiation from the solar spectrum and combine impact ionisation and impurity photovoltaic (PV) effect as well as making use of IR photons from the surroundings when fully optimised.

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Section: Summary Of Electrodeposition Of Cdte Resultsmentioning

confidence: 93%

“…This data enables the plotting of Mott-Schottky graphs (Figure 16b [3,[33][34][35]. These measurements also enable the estimation of the width of the depletion region at zero bias conditions.…”

Section: Capacitance-voltage (C-v) Measurementsmentioning

confidence: 94%

Fabrication of CdS/CdTe-Based Thin Film Solar Cells Using an Electrochemical Technique

et al. 2014

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“…Figure 2 also indicates the possible doping concentration changes assuming 10 10 cm -3 for intrinsic CdTe [7]. The literature indicates that the highest CdS/CdTe solar cell efficiencies are obtained for * 5.0 9 10 13 -5.0 9 10 15 cm -3 doping concentrations [8][9][10][11]. This region is shaded in Fig.…”

Section: Ultraviolet Photoelectron Spectroscopymentioning

confidence: 98%

Study of Fermi level position before and after CdCl2 treatment of CdTe thin films using ultraviolet photoelectron spectroscopy

Dharmadasa

Echendu

Fauzi

et al. 2016

J Mater Sci: Mater Electron

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The CdCl 2 treatment used in the development of high efficiency CdTe solar cells is an essential processing step but remains fully unexplored. What really happens during this treatment is not yet fully understood. The changes in doping concentrations during this processing step are a key parameter to investigate. Determination of the position of the Fermi level (FL) is a good method to explore these changes and therefore photoelectrochemical cell method and ultraviolet photoelectron spectroscopy method have been used to investigate these trends. Four different CdTe layers prepared by electroplating have been used for this investigation. The overall observations indicate the settling down of the FL in the upper half of the bandgap after CdCl 2 treatment.

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“…The numerical figures shown on the curve CiC' are some possible examples and 10 13 -10 15 cm −3 doping range could arise within the shaded region. All high efficiency CdTe solar cells have experimentally measured doping concentrations in this range [8,37,38]. Therefore electroplating provides a good method of controlling doping concentrations in CdTe without adding any external dopant to the material.…”

Section: Doping Variation In Cdtementioning

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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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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Influence of annealing in different chlorides on the photovoltaic parameters of CdS/CdTe solar cells

Cited by 40 publications

References 5 publications

Fabrication of CdS/CdTe-Based Thin Film Solar Cells Using an Electrochemical Technique

Fabrication of CdS/CdTe-Based Thin Film Solar Cells Using an Electrochemical Technique

Study of Fermi level position before and after CdCl2 treatment of CdTe thin films using ultraviolet photoelectron spectroscopy

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

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