Effects of multi-defects at metal/semiconductor interfaces on electrical properties and their influence on stability and lifetime of thin film solar cells

Dharmadasa, I. M.; Bunning, John D.; Samantilleke, A. P.; Shen, Tiehan H.

doi:10.1016/j.solmat.2004.08.009

Cited by 43 publications

(37 citation statements)

References 9 publications

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“…It is important at this point to comment on the unusual high Jsc values observed for these devices as shown in Table 1 and Figure 9. To do this, we recall the existence of several native defect/impurity levels within the energy bandgap of CdTe which are known to cause Fermi level pinning phenomenon at CdTe/metal interfaces [28,32,35]. Two of such impurity levels have been shown in the energy band diagram in Figure 3b for illustration.…”

Section: Resultsmentioning

confidence: 99%

Graded-Bandgap Solar Cells Using All-Electrodeposited ZnS, CdS and CdTe Thin-Films

Echendu

Dharmadasa

2015

Energies

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Abstract:A 3-layer graded-bandgap solar cell with glass/FTO/ZnS/CdS/CdTe/Au structure has been fabricated using all-electrodeposited ZnS, CdS and CdTe thin layers. The three semiconductor layers were electrodeposited using a two-electrode system for process simplification. The incorporation of a wide bandgap amorphous ZnS as a buffer/window layer to form glass/FTO/ZnS/CdS/CdTe/Au solar cell resulted in the formation of this 3-layer graded-bandgap device structure. This has yielded corresponding improvement in all the solar cell parameters resulting in a conversion efficiency >10% under AM1.5 illumination conditions at room temperature, compared to the 8.0% efficiency of a 2-layer glass/FTO/CdS/CdTe/Au reference solar cell structure. These results demonstrate the advantages of the multi-layer graded-bandgap device architecture over the conventional 2-layer structure. In addition, they demonstrate the effective application of the two-electrode system as a simplification to the conventional three-electrode system in the electrodeposition of semiconductors with the elimination of the reference electrode as a possible impurity source.

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Section: Resultsmentioning

confidence: 99%

Graded-Bandgap Solar Cells Using All-Electrodeposited ZnS, CdS and CdTe Thin-Films

Echendu

Dharmadasa

2015

Energies

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“…However, when the CdTe layer remains n-type after growth and post-growth treatment, a very different device is formed. Because of the Fermi level (FL) pinning at n-CdTe/metal interface [3,5] a large Schottky barrier (SB) can be formed at this interface. As a result, a CdS/CdTe/metal structure forms an n-n + SB structure with two PV active junctions.…”

Section: Introductionmentioning

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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“…A combination of the PEC and PL results indicates that the presence of carbon atoms in the CdTe grown with graphite anode tends to cause the movement of the Fermi level of the CdTe towards the valence band edge in the post-deposition annealing process as indicated in figure 8 (a), thereby making the material display p-type conductivity. This situation is also most likely encouraged by the Fermi level pinning phenomenon that is well-known to be pronounced in CdTe [29]. Table 4: Summary of defect levels observed in electrodeposited CdTe thin films using photoluminescence study at 80 K for CdTe grown using graphite anode and platinum anode [28].…”

Section: Photoelectrochemical (Pec) Cell Studymentioning

confidence: 99%

The effects of anode material type on the optoelectronic properties of electroplated CdTe thin films and the implications for photovoltaic application

Echendu

Dejene

Dharmadasa

2018

Journal of Physics and Chemistry of Solids

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Effects of multi-defects at metal/semiconductor interfaces on electrical properties and their influence on stability and lifetime of thin film solar cells

Cited by 43 publications

References 9 publications

Graded-Bandgap Solar Cells Using All-Electrodeposited ZnS, CdS and CdTe Thin-Films

Graded-Bandgap Solar Cells Using All-Electrodeposited ZnS, CdS and CdTe Thin-Films

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

The effects of anode material type on the optoelectronic properties of electroplated CdTe thin films and the implications for photovoltaic application

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