Browsing by Author "Namawardana, D.G.K.K."

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Effects of ZnO on inverted P3HT:PCBM bulk heterojunction solar cells
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Wanigasekara, G.; Namawardana, D.G.K.K.; Wanninayake, W.T.M.A.P.K.,; Jayathilaka, K.M.D.C.,; Wijesundera, R.P.; Siripala, W.
Low cost, low environmental impact, ease of mass production and many more promising attributes of Organic Solar Cells (OSCs) have inspired researchers to investigate OCSs for increasing their performance and stability in a constant phase. Moreover, in the recent years, OSCs with inverted structures have gained more attention compared to the conventional configuration of the device. In this study, Indium Tin Oxide (ITO) -free inverted OSC devices were fabricated on polished Stainless Steel (SS) substrates with top illumination in order to have the device structure of SS/ZnO/P3HT:PCBM/PEDOT:PSS/Au. A thin film of Zinc Oxide (ZnO) layer was deposited on SS substrates from a solution of Zinc Acetate Dihydrate (ZnC₄H₆O₄·2H2O) using spin coating technique. The active layer was spin-coated from a bulk heterojunction polymer blend of regioregular Poly(3-hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM) on the prepared ZnO layer. On the top of the active layer, Ethylene glycol doped poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was blade coated as the hole transport layer. Then the stack was annealed before Gold (Au) was sputter coated to make the top contact. The device performance was optimized by varying a number of parameters including the concentration of ZnC₄H₆O₄·2H2O solution, thickness of the ZnO layer, annealing temperature, annealing time, composition of the polymer blend and dopant material of PEDOT:PSS dispersion. Open circuit voltage (Voc) and short circuit current (Jsc) of the devices increased after applying ZnO layer. The thermal annealing improved the fill factor (FF) of the devices. Spectral response measurements reveal that photon energies higher than 1.77 eV are absorbed by the device and photogenerated electron-hole pairs are produced. The best OSC device exhibited Voc of 440 mV with the Jsc of 6.2 mA/cm2 , fill factor (FF) of 30% and maximum power conversion efficiency of 0.05%.
Electrodeposited ZnS Thin Films for NO2 Gas Sensing Applications
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Wickramathilaka, P.A.K.Y.; Namawardana, D.G.K.K.; Atapattu, H.Y.R; De Silva, D.S.M.
Sensors are becoming a consequential part in human’s daily life. Typically, they are classified based on the physical parameter sensed itself namely; thermal, mechanical, magnetic, chemical, and optical. Gas sensors are chemical sensors that can be fabricated as metal-oxide or metal-sulfide semiconductor materials viz.; TiO2, ZnO, CdS and ZnS etc. Among these materials ZnS is a highly abundant and non-toxic material and can be easily adopted for gas sensing applications. Electrodeposition can be identified as an ideal fabrication method owing to its simplicity and low cost in production amid various fabrication methods that have been employed for developing ZnS thin films. This study focuses on the growth of ZnS thin films for gas sensing applications using the technique of electrodeposition. A three electrode electrolytic system consists of an Ag/AgCl reference electrode, FTO glass substrate (1×3 cm2) working electrode and high purity carbon counter electrode was used in electrodepositing ZnS material in an aqueous electrolyte containing ZnCl2 (0.10 - 0.05 mol/L) and Na2S2O3 (0.01 - 0.05 mol/L) precursors. The ZnS depositions were carried out in the cathodic deposition potential (CDP) range of 0.70 - 1.10 V and pH range of 4.0 - 3.5 at temperature of 30 °C for 90 minutes. After deposition, samples were annealed at 300 °C for 10 minutes and characterized for their crystalline structure, surface morphology and elemental composition using the techniques of X-ray diffraction spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy respectively. The sample grown at CDP of 1.05 V at pH of 3.7 were found to have notable material properties and shown 2 Ω average change in resistance with respect to the initial average resistance of 26.2 Ω while exposing to NO2 gas at 3× 104 Pa and 30 °C within a time interval of 2-3 minutes
Fabrication of inverted polymer based organic solar cells on stainless steel substrate
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Namawardana, D.G.K.K.; Wanigasekara, G.; Wanninayake, W.T.M.A.P.K.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.
In the past years, polymer based organic solar cells (OSCs) have become a widely researched topic as a potential candidate for producing clean and renewable energy due to their lightweight, high mechanical flexibility, and large-area processability. As an alternative for the conventional device structure, in this study, OSC devices with an inverted structure were fabricated and characterized under the top illumination. Regioregular poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) were used as the electron donor and electron acceptor material respectively for the device fabrication with structure of SS/P3HT:PCBM/PEDOT:PSS/Au. On pre-cleaned stainless steel (SS) substrates, bulk heterojunction polymer blend was spin coated from chlorobenzene solution (20 mg/mL) with a 1:1 weight ratio of P3HT: PCBM and then it was thermally annealed. As a hole-transport-layer (HTL), a thin film of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) doped with ethylene glycol (10 wt.%) was blade coated on the active layer and the stack was annealed at 120ºC for 10 minutes. As the top contact of the device, gold (Au) was sputter coated. Performances of the fabricated OSC devices were optimized by varying several discrete parameters including the spin rate of the active layer formation, annealing temperature and the annealing time of the active layer. The optimum conditions for the device fabrication with the best performance were at the spin rate of 3000 rev./min for the active layer formation whereas optimum annealing temperature and annealing time were 160ºC and 60 minutes, respectively. The best device produced had an open-circuit voltage (Voc) of 238 mV and a short-circuit current density (Jsc) of 4.36 mAcm-2 . A maximum power conversion efficiency (PCE) of 0.02% with a fill factor (FF) of 23.16% was obtained under 1 sun illumination (AM 1.5G, 1000 Wm-2 ). The spectral response measurements of the fabricated cell indicate that it absorbs photons with energy higher than 1.77 eV to generate electron-hole pairs. It is planned to fabricate a thin film of Zinc Oxide (ZnO) as a potential electron transport layer (ETL) on SS substrate to improve the FF and PCE of the device.