2020-02

BACG, United Kingdom

Attendance

2015-12

Proceedings of the International Postgraduate Research Conference, University of Kelaniya, Kelaniya, Sri Lanka.

Thin films of CdS and CdTe semiconductor materials were electrodeposited onto glass/fluorine doped tin oxide conducting glass surfaces using a potentiostat/galvanostat equipped with a three electrode cell. Aqueous electrolytic bath containing CdCl2 and (NH4)2S2O3 was used for the electrodeposition of CdS thin films. CdTe thin films were electrodeposited onto glass/FTO/CdS substrates from aqueous solution having high concentrations of CdSO4 and low concentrations of TeO2 and CdCl2. The glass/FTO/CdS/CdTe/Cu-Au solar cell devices were prepared by thermal evaporation of Cu and Au on CdTe surface. CdS films grown were annealed at ~400 °C for 15 minutes in air and photo-electro chemical (PEC) cell measurements were performed to identify the electrical conductivity type. Both as-deposited and annealed CdS layers were identified as n-type in electrical conduction. CdS thin films were shown enhanced PEC responses upon heat treatment. The respective band gap values for as-deposited and heat treated CdS were 2.35±0.05 eV and 2.40±0.05 eV which were close to the band gap of bulk CdS. XRD analysis of as-deposited CdS layers revealed the presence of hexagonal CdS materials with the major peak arising from (002) plane. Following the CdTe deposition on glass/FTO/CdS substrate, the surface of CdTe layers were coated with a 0.1% CdCl2 solution and structures were annealed at ~400°C for 10 minutes in air. Band gaps for CdTe layers were found to be 1.45±0.02 eV for both as-deposited and annealed samples which exhibited the band gap of bulk CdTe. There was a little improvement in cubic (220) and (311) peaks of XRD spectra of annealed CdTe layers compared to the as-deposited material, but annealing exhibited a small reduction of cubic phase preferential orientation (111). SEM images showed that CdS and CdTe layers were fairly uniform. The fabricated solar cell devices showed the efficiency of 2.1% with Voc ~330 mV, Jsc~20 mA cm-2 and FF~33% under the illumination of air mass (AM) 1.5 conditions (100 mW/cm2 , 1 Sun).

2015-07

UK Semiconductors & UK Nitrides Consortium Summer Meeting, Sheffield, United Kingdom

CdTe thin films were electrodeposited (ED) using acidic aqueous solution containing 1.0 M Cd(NO3)2 4H2O and 1.0 mM TeO2. The deposition of the CdTe thin films were carried out cathodically using 2-electrode system on the glass/FTO substrate. The ED-CdTe layers were heat treated with CdCl2 and CdCl2+CdF2 at three different temperatures of 385oC, 420oC and 450oC and results were compared with the as grown layers. The structural, morphological and optical properties of the CdTe layers were carried out using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and optical absorption. The observation reveals the drastic improvements in the structural, morphological and optical properties of ED-CdTe thin films after annealing at 450oC in the presence of CdCl2 and CdCl2+CdF2 treatment as compared to annealing temperature of 385oC and 420oC. Keywords: Electrodeposition, CdTe, thin film, semiconductor, CdCl2 & CdF2

2015-04

Proceedings of the 11th Photovoltaic Science, Applications and Technology Conference C97 (PVSAT-11), University of Leeds.

Current solar cells under research and development utilise mainly one absorber layer limiting the photon harvesting capabilities. In order to develop next generation solar cells, research should move towards effective photon harvesting methods utilising low-cost solar energy materials. This will lead to reduce the $W−1 figure for direct solar energy conversion to electrical energy. In this work, a graded bandgap solar cell has been designed to absorb all photons from the UV, visible and IR regions. In addition, impurity PV effect and impact ionisation have been incorporated to enhance charge carrier creation within the same device. This new design has been experimentally tested using the most researched MOCVD grown GaAs/AlGaAs system, in order to confirm its validity. Devices with high Voc ~ 1175 mV and the highest possible FF ~ (0.85–0.87) have been produced, increasing the conversion efficiency to ~20% within only two growth runs. These devices were also experimentally tested for the existence of impurity PV effect and impact ionisation. The devices are PV active in complete darkness producing over 800 mV, Voc indicating the harvesting of IR radiation from the surroundings through impurity PV effect. The quantum efficiency measurements show over 140% signal confirming the contribution to PV action from impact ionisation. Since the concept is successfully proven, the low-cost and scalable electrodeposited semiconducting layers are used to produce graded bandgap solar cell structures. The utilisation of nano- and micro-rod type materials in graded bandgap devices are also presented and discussed in this paper. Preliminary work on glass/FTO/n-ZnS/n-CdS/n-CdTe/Au graded bandgap devices show 10%–12% efficient devices indicating extremely high Jscvalues ~48 mA·cm−2, showing the high potential of these devices in achieving higher efficiencies.

2015-04

Proceedings of the 11th Photovoltaic Science, Applications and Technology Conference C97 (PVSAT-11), University of Leeds, Leeds, United Kingdom.

Cadmium sulphide (CdS) thin films have been electrodeposited on glass/FTO substrate using a 2-electrode system from combination of thiourea (CH4N2S) and cadmium chloride hydrate (CdCl2 xH2O) precursors. The thin films were characterised using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Photoelectrochemical (PEC) cell and Optical absorption to study their structural, morphological, electrical and optical properties. XRD results show that the layers are polycrystalline in nature having hexagonal crystal structure with preferred orientation along (200) plane. SEM spectra indicate an increase in grain size from ~100 nm to ~300 nm after heat treatment. The increase in the magnitude of the PEC signal was observed after CdCl2 heat treatment as compared to the as-deposited layers. Observation from optical absorption reveals that the bandgap values of thin films lies in the range of 2.22 to 2.58 eV. In general, after normal annealing in air and CdCl2 heat treatment bandgap values improve and shifts close to the bulk bandgap value of CdS (2.42 eV). Work is continuing to optimise the electronic quality of these layers for incorporation in thin film solar cells.

2015-04

Proceedings of the 11th Photovoltaic Science, Applications and Technology Conference C97 (PVSAT-11), University of Leeds, Leeds, United Kingdom.

Cadmium telluride (CdTe) thin films have been successfully prepared from an aqueous electrolyte bath containing cadmium chloride (CdCl2).H2O and tellurium dioxide(TeO2) using electrodeposition technique. The structural, electrical, microstructuraland opticalproperties of these thin films have been characterized using XRD, photo-electro-chemical (PEC) cell, D.C. conductivitymeasurements,SEM and UV-Vis spectrophotometry. It is observed that the bestcathodic potential is698mVwith respect to standard calomel electrode. The work is progressing to fabricate solar cells and compare with CdTe, grown by conventional sulphate precursors .

2014-09

29th European Photovoltaic Solar Energy Conference and Exhibition, Amsterdam, Netherlands (EU PVSEC)

Poster

2014-07

UK Semiconductors & UK Nitrides Consortium Summer Meeting, Sheffield Hallam University, Sheffield, United Kingdom.

Electrodeposition (ED) of CdTe thin films are usually grown using cadmium sulfate (CdSO4) as the precursor for Cd ions. In this work CdTe thin film has been electrodeposited on glass/FTO substrate from cadmium nitrate (Cd(NO3)2.4H2O) as the precursor for Cd ions using simplified 2-electrode system. Both asdeposited & CdCl2-treated layers were characterised using XRD, PEC, SEM and Optical absorption. Before the growth and process optimisation, the initial solar cells device structures of glass/FTO/CBD-CdS/ED-CdTe/Au fabricated with the electrodeposited CdTe layers show PV activity with solar cell output parameters of V oc = 605 mV, Jsc= 25.5 mAcm-2, FF = 0.41, and η = 6.3%. The work is progressing to develop the devices based on this material.

2014-04

Proceeding of the 10th Photovoltaic Science, Application and Technology (PVSAT-10), Loughborough University, Loughborough, UK

Electrodeposition (ED) of CdTe thin films are usually grown using cadmium sulfate (CdSO4) as the precursor for Cd ions. In this work CdTe thin film has been electrodeposited on glass/FTO substrate from cadmium nitrate (Cd(NO3)2.4H2O) as the precursor for Cd ions using simplified 2-electrode system. Both asdeposited & CdCl2-treated layers were characterised using XRD, PEC, SEM, TEM and Optical absorption. Before the growth and process optimisation, the initial solar cells device structures of glass/FTO/CBD-CdS/ED-CdTe/Au fabricated with the electrodeposited CdTe layers show PV activity with solar cell output parameters of Voc = 605 mV, Jsc= 25.5 mAcm-2, FF = 0.41, and η = 6.3%. The work is progressing to develop the devices based on this material.

2013-08

2nd International Conference on Solar Energy Materials, Solar Cells and Solar Energy Applications (SOLAR ASIA), Willayah Persekutuan, Malaysia.

Poster

2013-07

UK Semiconductors & UK Nitrides Consortium Summer Meeting, Sheffield, United Kingdom.

Poster

2013-06

Proceedings of the 9th Photovoltaic Science, Applications and Technology Conference C95, , (2013) 79-82At: Swansea, United Kingdom

Low-cost electroplating has been used to deposit thin layers of ZnS, CdS and CdTe. Results of scanning electron microscopy (SEM) and 3D atomic force microscopy (3D-AFM) reveal that the window materials grown on glass/FTO substrates consists of uni-directional and compact nano-rods and the absorber material grown on glass/FTO/CdS consists of rods or columnar-shaped grains with much larger cross-sections. Fully processed glass/FTO/ZnS/CdS/CdTe/Metal structures show varying photovoltaic parameters exhibiting up to 10.4% conversion efficiencies with excessively large Jsc values arising due to existence of rod-type material structures in nano-scale. Advantages and disadvantages of these device structures are presented in this paper.

2013-06

39th IEEE Photovoltaic Specialist Conference, Florida, United States

Low-cost electroplating has been used to deposit thin layers of ZnS, CdS and CdTe. Results of scanning electron microscopy (SEM) and 3D atomic force microscopy (3D-AFM) reveal that the window materials grown on glass/FTO substrates consists of uni-directional and compact nano-rods and the absorber material grown on glass/FTO/CdS consists of rods or columnar-shaped grains with much larger cross-sections. Fully processed glass/FTO/ZnS/CdS/CdTe/Metal structures show varying photovoltaic parameters exhibiting up to 10.4% conversion efficiencies with excessively large Jsc values arising due to existence of rod-type material structures in nano-scale. Advantages and disadvantages of these device structures are presented in this paper (2) (PDF) Thin film photovoltaic solar cells with nano- and micro-rod type II-VI semiconducting materials grown by electroplating. Available from: https://www.researchgate.net/publication/262041660_Thin_film_photovoltaic_solar_cells_with_nano-_and_micro-rod_type_II-VI_semiconducting_materials_grown_by_electroplating [accessed Mar 02 2019].

2012-11

4th Association of Professional Sri Lankans Convention, APSL - Research Symposium (APSL-RS), Sheffield, United Kingdom

Poster