High short-circuit current density CdTe solar cells using all-electrodeposited semiconductors

Echendu, O. K.; Fauzi, F.; Weerasinghe, A R; Dharmadasa, I. M.

doi:10.1016/j.tsf.2014.01.071

Cited by 63 publications

(54 citation statements)

References 17 publications

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“…The efforts are also directed to gain optimum benefits from grain boundary enhanced PV effects, as described above. One device structure tested using already established materials, glass/FTO/n-ZnS/n-CdS/n-CdTe/Au has shown 10.4% efficiency [60], exhibiting extremely high J sc values as expected. Its energy band diagram is shown in Fig.…”

Section: Progress To Date On Graded Bandgap Devicessupporting

confidence: 52%

“…NaOH, KOH, hydrazene hydrate etc are good examples of these etchants. A few seconds etch in oxidizing etch (dilute K 2 Cr 2 O 7 in H 2 SO 4 ) followed by ~2 min treatment in reducing etch (aqueous solution of NaOH + Na 2 S 2 O 3 ) proved to produce Cd-rich surfaces, leading to high Schottky barrier formation at n-CdTe/metal interfaces [3,[58][59][60][61].…”

Section: Chemical Etching Prior To Metallisationmentioning

confidence: 99%

“…As described in numerous publications afterwards [8,60,61] and summarised in this review, CdTe can be prepared to form both p-type (when Te rich) and n-type (when Cd rich) material after CdCl 2 treatment. Therefore, the CdS/CdTe device structures were fabricated and studied in this research programme, in the vicinity of V i producing both p-CdTe and n-CdTe for fabrication of devices.…”

Section: Cds/cdte Device Issuesmentioning

confidence: 99%

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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: Progress To Date On Graded Bandgap Devicessupporting

confidence: 52%

Section: Chemical Etching Prior To Metallisationmentioning

confidence: 99%

Section: Cds/cdte Device Issuesmentioning

confidence: 99%

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

Dharmadasa

Ojo

2017

J Mater Sci: Mater Electron

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“…Chemical etching is carried out using different techniques in different research laboratories. These methods are widely published in the literature [17,[25][26][27]. In the main author's research programme, the surface is etched for ~10 s in an oxidizing chromic acid solution, followed by reducing etch consisting of Na 2 S 2 O 3 and NaOH in water.…”

Section: Preparation Of the Back Metal Contactmentioning

confidence: 99%

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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“…The pH of the electrolyte was adjusted to 2.0±0.02 and CdTe layers were electrodeposited at a cathodic voltage of 2038 mV and temperature of 85.0±2.0°C. Full details of the electrodeposition of CdTe thin films using two-electrode system is reported in recent publications [23,24]. Optical characterisation of all the annealed and as-deposited CdTe samples was carried out using a Cary 50 UV-VIS Spectrophotometer (Varian, Australia) by recording the normalincidence transmittance spectra in the photon wavelength range of (750 -1000) nm.…”

Section: Methodsmentioning

confidence: 99%