Effect of CdCl2 activation on the impurity distribution in CdTe/CdS solar cell structures

Emziane, Mahieddine; Durose, K.; Romeo, N.; Bosio, A.; Halliday, D.P.

doi:10.1016/j.tsf.2004.11.053

Cited by 44 publications

(51 citation statements)

References 25 publications

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“…There are also other implications on the analysis of depth profiling results of CdCl 2 treated poly-crystalline CdTe layers [69]. As described above, the impurities like Cl and O can freely flow along the melted grain boundaries down to the CdS layer.…”

Section: Grain Boundary Enhanced Pv Effectmentioning

confidence: 96%

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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Section: Grain Boundary Enhanced Pv Effectmentioning

confidence: 96%

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

Dharmadasa

Ojo

2017

J Mater Sci: Mater Electron

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“…Impurity analysis has also been carried out using secondary ion mass spectroscopy (SIMS) profiling [43] in order to study the CdCl 2 treatment. Although SIMS is a well-established analytical tool, the practical issue is to decide which impurity to study and how to quantify these impurities present from the profiles.…”

Section: Impurity Incorporation In Devices Via Cdclmentioning

confidence: 99%

Review of the CdCl2 Treatment Used in CdS/CdTe Thin Film Solar Cell Development and New Evidence towards Improved Understanding

2014

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Cadmium chloride treatment is a key processing step identified in the late 1970s to drastically improve the solar to electric conversion efficiency of CdS/CdTe thin film solar cells. Although a large body of experimental results are available to date, this process is yet to be understood even after three decades of research. This paper reviews the experimental results available, presents some new clues leading to improved understanding and suggests key research areas necessary to fully understand this crucial processing step. Improved understanding will lead to further increase in conversion efficiency of CdS/CdTe solar cells well beyond 20%.

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“…Although the latter is not likely to occur in such small-grained material, we approximate = ∞ with the center of the grain in the inset of Cl is the only shallow donor species likely to exist in such high concentrations (~10 17 cm -3 ) 21,22 in as-deposited CSS material -likely originating from the CdTe source material. If Cl is involved in both the Z-band DAP transition and the A-center transition, it may be expected that random compositional inhomogeneity could result in a close spatial relationship between Z-band and A-center luminescence.…”

Section: Resultsmentioning

confidence: 99%

Explanation of red spectral shifts at CdTe grain boundaries

Moseley

Al‐Jassim

Moutinho

et al. 2013

Applied Physics Letters

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The best research-cell efficiencies for CdTe thin-film solar cells have recently increased from 17.3% to 20.4%. Despite these impressive recent gains, many improvements in device technology are necessary to reach the detailed-balance efficiency limit for CdTe-based (singlejunction, non-concentrator) solar cells of ~32%. Improvements will increasingly rely on knowledge of the fundamental relationships between processing, electrical properties of defects, and device performance. In this study, scanning electron microscope (SEM)-based cathodoluminescence (CL) spectrum imaging was used to examine these fundamental relationships. In CL spectrum imaging we collect a spectrum per pixel in a 256 × 256 pixel SEM image by synchronizing a cryogenic silicon charge-coupled device with the electron-beam positioning. High spatial resolution photon energy maps obtained with this technique can reveal intricate luminescence phenomena that are not apparent in spectroscopic data.

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Effect of CdCl2 activation on the impurity distribution in CdTe/CdS solar cell structures

Cited by 44 publications

References 25 publications

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

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

Review of the CdCl2 Treatment Used in CdS/CdTe Thin Film Solar Cell Development and New Evidence towards Improved Understanding

Explanation of red spectral shifts at CdTe grain boundaries

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