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Fabrication of CdS/CdTe Thin Film Solar Cells via the Technique of Electrodeposition
(Development of Solar Power Generation and Energy Harvesting, 2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Ojo, A.A.; Dharmadasa, I.M.
This study focused on fabrication of CdS/CdTe solar cells using the technique of electrodeposition as it is simple, low cost and scalable method. Initially, CdS and CdTe materials were individually deposited on fluorine doped tin oxide (FTO) glass substrates and optimum growth conditions were obtained by analyzing their structural, compositional, electrical, optical and morphological properties using the techniques of X-ray diffraction, Energy Dispersive X-ray spectroscopy, photo-electrochemical cell study, optical absorption spectroscopy and scanning electron microscopy respectively. Thereafter, final device structure ofglass/FTO/CdS/CdTe/Au was fabricated using the optimum growth conditions obtained for the two materials, CdS and CdTe. Finally the current density-voltage characteristics of the devices were obtained to assess devices. The best device structure exhibited short circuit current density (L) of 24.4 mA cm- 2, open circuit voltage (V) of 681.9 mV, Fill Factor (FF) of 0.32 and conversion efficiency of 5.4 per cent.
Post deposition surface treatments to enhance the quality of polycrystalline CdTe thin films for photovoltaic applications
(Nit teria1s Chemi stry and Physics 213 (201S) 4065113, 2018) Atapattu, H.Y.R.; De Silva, D.S.M.; Pathirane, K.A.S.
Cadmium telluride (CdTe) is one of the topmost thin film polycrystalline materials used in the photo¬voltaics (PV) industry today and post deposition surface treatment has been a major step used in the production process for improving the photovoltaic quality of the CdTe material. In the present study, several post deposition surface treatment processes including CdCl2 treatment were carried out on CdTe material and the properties of the materials were then analyzed with the intension of gaining an un¬derstanding of the effect of the post deposition process on the material properties and identifying better post deposition treatment processes that can be used to improve the PV quality of the material. In this study, CdTe thin films were potentiostatically electrodeposited using the typical three electrode elec¬trolytic cell consisted of a saturated calomel reference electrode and a high purity graphite counter electrode. 3Cd504.8H20 and Te02 were used as the cadmium and the tellurium precursors respectively and CdTe layers were electrodeposited on fluorine doped tin oxide (ETD) glass substrates and glass/PTO/ CdS surfaces at pre-identified growth conditions namely; cathodic deposition potential of 650 mV, pH of 2.3 and temperature of 65'C. Subsequently, deposited samples were annealed in air with CdCl2 and thereafter, comparable samples of glass/FTO/CdTe and glass/FTO/CdS/CdTe were subjected to surface etching with diluted HCl (DH), Br2-CH3OH (BM), HNO3-H3PO4 (NP), K2Cr2D7-H2504 (DS) and K2Cr207- CH3OH (DM). Surface treated samples were then characterized for their electrical, optical, elemental, morphological and structural properties using photo-electrochemical cell measurements, optical ab¬sorption spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction spectroscopy respectively. The study reveals that, post deposition surface treatments with BM and NP etchings enhance the material qualities of polycrystalline CdTe layers to be used for fabrication of PV devices.
Electrodeposition of well-adhered CdTe thin films for solar cell applications
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.
Among the second generation thin film photovoltaics, CdS/CdTe based solar cell device is one of the leading contenders for large scale commercialization. Since the CdTe is the crucial absorber material of the foregoing device, it is essential to maintain a well-adhered CdTe layer to obtain high photovoltaic activities. If not, loosened CdTe layers with numerous pinholes can reduce the electrical, optical, structural and morphological properties of the material and hence extinguish the entire activities of CdS/CdTe solar cells. In the present study, an electrodeposition procedure was developed to fabricate welladherent CdTe layers to the substrate using the typical three electrode electrolytic cell. A fluorine doped tin oxide conducting glass substrate (7Ω/sq.) with dimensions of (1×3) cm2 was used as the working electrode in the cell. A saturated calomel electrode and a high purity graphite rod served as reference and counter electrodes respectively. All the electrodepositions were carried out using an aqueous solution containing 1.0 mol/L CdSO4, 1.0 mmol/L TeO2 and 5.5 mmol/L CdCl2. Based on the cyclic voltammetry studies and the stoichiometry of the proposed chemical reaction which forms CdTe material, the possible cathodic deposition potential (CDP) and pH ranges were identified to be in the ranges of 550-710 mV and 1.4-2.4 respectively. Henceforth, CdTe layers were electrodeposited at above mentioned conditions at temperature of 65 °C and subsequently annealed in air at 400 °C for 10 min. Thereafter, by considering the physical appearance of deposited CdTe layers and their adhesiveness upon a high pressure N2 flow, the feasible values for CDP and pH were found to be in the ranges of 590-660 mV and 2.0-2.4 respectively. To further fine-tune the values for CDP and pH, a series of CdTe layers were deposited at above feasible growth conditions and inspected for their electrical, optical, structural and morphological properties using the methods of photo-electrochemical cell, optical absorption spectroscopy, X-ray diffraction and scanning electron microscopy respectively. Results revealed that, the optimum CDP is in the range of 620-660 mV and pH is in the range of 2.1-2.3 to exhibit good photovoltaic qualities.

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