Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy

Luria, Justin; Kutes, Yasemin; Moore, Andrew; Zhang, Lihua; Stach, Eric A.; Huey, Bryan D.

doi:10.1038/nenergy.2016.150

Cited by 72 publications

(87 citation statements)

References 34 publications

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“…Our findings that contain what appears to be planar defects or twin boundaries, consistent with those observed in Ref. [12]. The field of view for all images is 48 μm.…”

Section: Resultssupporting

confidence: 91%

Effects of CdCl2 treatment on the local electronic properties of polycrystalline CdTe measured with photoemission electron microscopy

Berg

Kephart

Sampath

et al. 2017

2017 IEEE 44th Photovoltaic Specialist Conference (PVSC)

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To investigate the effects of CdCl 2 treatment on the local electronic properties of polycrystalline CdTe films, we conducted a photoemission electron microscopy (PEEM) study of polished surfaces of CdTe films in superstrate configuration, with and without CdCl 2 treatment. From photoemission intensity images, we observed the tendency for individual exposed grain interiors to vary in photoemission intensity, regardless of whether or not films received CdCl 2 treatment. Additionally, grain boundaries develop contrast in photoemission intensity images different from grain interiors after an air exposure step, similar to observations of activated grain boundaries using scanning Kelvin probe force microscopy studies. These results suggest that work function varies locally, from one grain interior to another, as well as between grain boundaries and grain interiors.

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“…Our findings that contain what appears to be planar defects or twin boundaries, consistent with those observed in Ref. [12]. The field of view for all images is 48 μm.…”

Section: Resultssupporting

confidence: 91%

Effects of CdCl2 treatment on the local electronic properties of polycrystalline CdTe measured with photoemission electron microscopy

Berg

Kephart

Sampath

et al. 2017

2017 IEEE 44th Photovoltaic Specialist Conference (PVSC)

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“…Therefore, this minimise the recombination mechanism in these devices and the density of photo-generated currents are high in grain boundaries. This has been clearly demonstrated by recent EBIC results of the cross-sections of CdS/CdTe solar cells [67,68]. In this type of grain boundary enhanced PV actions, only one type of charge carriers flow along the grain boundaries and any defects present will be saturated instantaneously upon illumination and then show high quality electrical conduction.…”

Section: Grain Boundary Enhanced Pv Effectmentioning

confidence: 79%

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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“…In 2015, Buckwell et al [22] used scalpel AFM to analyze CNFs in W/SiOX/TiN samples; however, the diameter of the CNFs observed was much wider (Ø > 500 nm), which may not correspond to that of real RS devices under normal operation. And in 2016, Luria et al [38] used scalpel AFM to characterize polycrystalline 2.2 µm thick CdTe films for photovoltaic cells, and the granular structure of the CdTe film was successfully displayed, showing conductive grain boundaries wider than 100 nm. However, in these two works [22,38] the features studied had diameters much larger than the CNFs displayed by the IMEC group, and it is a fact that in five years no other group has reported the characterization of the 3D shape and 3D currents of nanosized CNFs (Ø <30 nm) across amorphous thin (<10 nm) oxides using scalpel AFM.…”

Section: Introductionmentioning

confidence: 99%

On the Limits of Scalpel AFM for the 3D Electrical Characterization of Nanomaterials

Chen

Jiang

Buckwell

et al. 2018

Adv Funct Materials

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Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy

Cited by 72 publications

References 34 publications

Effects of CdCl2 treatment on the local electronic properties of polycrystalline CdTe measured with photoemission electron microscopy

Effects of CdCl2 treatment on the local electronic properties of polycrystalline CdTe measured with photoemission electron microscopy

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

On the Limits of Scalpel AFM for the 3D Electrical Characterization of Nanomaterials

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