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Item Thin film cuprous oxide homojunction photoelectrode for water splitting(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Kafi, F. S. B.; Thejasiri, S. A. A. B.; Wijesundera, R. P.; Siripala, W.Employing cuprous oxide (Cu2O) photoelectrodes in photoelectrochemical cells to generate hydrogen by water splitting is beneficial. Conventionally, it is limited in practice because of the well-known reasons of its inherent corrosiveness and poor conversion efficiencies. In this study, we have investigated the possibility of improving the efficiency of Cu2O photoelectrode in the form of p-n homojunction together with sulphidation. Initially, the optimum pH values for the n- and p-Cu2O thin film deposition baths are determined as 6.1 and 13 for Ti/n-Cu2O/p-Cu2O in photoelectrochemical cell configuration. Then, at these pH values the duration of n- and p-Cu2O thin film deposition is optimized by forming Ti/n-Cu2O/p-Cu2O photoelectrode. In this study, we found that at 45 minutes of n-Cu2O and 50 minutes of p-Cu2O thin film deposition together with sulphidation forms relatively high efficient Ti/n-Cu2O/p-Cu2O photoelectrode resulting Solar-To- Hydrogen (STH) conversion efficiency of 0.9%. In addition, current-voltage characteristic of the best Cu2O homojunction photoelectrode exhibits more negative shift in onset of photocurrent which indicates that photocurrent generation and transportation have improved by the formation of homojunction and further been enhanced by sulphidation.Item 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%.Item 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.Item Comparison of the properties of CZTS semiconductor films grown by sequential and single step electrodeposition techniques(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Fernando, W.T.R.S.; Jayathilaka, K.M.D.C.; Wijesundera, R.P.; Siripala, W.Cu2ZnSnS4 (CZTS) is a promising semiconductor material suitable for application in low-cost and environmentally friendly thin film solar cells due to its superior optoelectronics properties. It is a perfect absorber material due to its high absorption coefficient (>10-4 cm-1 ) and direct optical bandgap (1.4-1.5 eV). Among the CZTS preparation techniques, electrodeposition is an attractive technique because of its simplicity, low cost and easy process controlling capability. In this investigation, a comparative study on CZTS films grown by two different techniques, namely, sequential electrodeposition and single step electrodeposition, has been carried out. Electrodeposition of Cu, Sn and Zn stack layers followed by sulphurisation with H2S is one of CZTS growth techniques. In this study, growth parameters of sequentially electrodeposited CZTS were optimized to obtain best photoactive CZTS thin films. Electrodeposition parameters of Cu, Sn and Zn have been obtained using voltammograms. Cu thin film was electrodeposited on Mo substrate at –0.89 V vs Ag/AgCl in an electrochemical cell containing 0.4 M CuSO4, 3 M lactic acid and NaOH at pH 11. Deposition of Sn thin film on Mo/Cu electrodes was carried out at -1.2 V vs Ag/AgCl in an electrochemical cell containing 0.055 M, 2.25 M NaOH and 8 ml of sorbitol. Zn thin film was electrodeposited on Mo/Cu/Sn at -1.2 V vs Ag/AgCl in an electrochemical cell containing 0.2 M ZnSO4. In order to grow CZTS, Mo/Cu/Sn/Zn thin films were annealed at 550 oC for 60 min in H2S. In the single step electrodeposition, CZTS thin films on Mo substrate were potentiostatically electrodeposited at -1.05 V vs Ag/AgCl for 40 min in a three electrode electrochemical cell containing 0.02 M copper (II) sulfate pentahydrate (CuSO4·5H2O), 0.01 M zinc sulfate heptahydrate (ZnSO4·7H2O), 0.02 M tin sulfate (SnSO4) and 0.02 M sodium thiosulfate (Na2S2O3) at room temperature. 0.2 M tri-sodium citrate (C6H5Na3O7) was used as the complexing agent and tartaric acid (C4H6O6) was used as the pH control solution. The pH of the bath was maintained at 5. The Ag/AgCl and platinum electrodes were used as the reference and the counter electrodes respectively. Then samples prepared were annealed at 550 oC for 30 min in H2S. CZTS films grown by two techniques were characterized using X-ray diffraction, reflectance, dark and light I-V, spectral response and C-V measurements in a PEC containing 0.1 M sodium acetate. Reflectance measurements reveal that the band gap energy of the films is 1.45 eV and I-V and spectral response measurements reveal that CZTS thin films were photoactive and p-type. The results obtained revealed that high quality photoactive CZTS can be prepared using both techniques. However, I-V and spectral response characteristics revealed that photoactive properties of CZTS thin films prepared by single step electrodeposition technique are superior in comparison to sequentially electrodeposited thin films.Item Enhancement of photovoltaic performance of Cu2O homojunction by introducing a ZnO buffer layer(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Thejasiri, S.A.A.B.; Kafi, F.S.B.; Wijesundera, R.P.; Siripala, W.Cuprous oxide (Cu2O) is a semiconductor material having the capability of producing a theoretical conversion efficiency of 20% which is acceptable for solar energy applications. In this investigation, we have explored the possibility of improving open circuit voltage (Voc) of Cu2O homojunctions by introducing a ZnO buffer layer in between n- and p-Cu2O layers. The thin buffer layer may be able to develop an additional potential drop across the interface improving Voc without hindering short-circuit current density (Jsc). In this investigation, n-Cu2O thin films were electrodeposited on Ti substrates at -200 mV vs Ag/AgCl for 30 minutes in an acetate bath. Samples were then annealed at 175 oC for 30 min in air. ZnO thin film was deposited on Ti/nCu2O film by employing Successive Ionic Layer Adsorption Reaction (SILAR) technique using 0.1 M Zn(NH3)4 2+ aqueous solution. Resulted samples were annealed at 175 oC for 10 minutes. pCu2O thin film was electrodeposited on Ti/n-Cu2O/ZnO electrode at -450 mV vs. Ag/AgCl for 45 minutes in a lactate bath. Surface of p-Cu2O was exposed to ammonium sulphide vapor in order to prepare an ultra-thin Cu2S layer. Finally, 2x2 mm2 Au spots were sputtered on the coper sulphide layer. A set of Ti/n-Cu2O/ZnO/p-Cu2O/Au devices having different thicknesses of ZnO layers was prepared by changing the number of successive adsorption cycles and characterized them by using dark and light current voltage measurements. Dark and light current voltage characteristics revealed that the device fabricated using 3 cycled ZnO layer produces the best photoactive performance. Without the buffer layer, the device produced Voc of 384 mV and Jsc of 8.1 mAcm-2 , under AM 1.5 illumination. With the ZnO buffer layer the device Voc improved up to 416 mV and Jsc up to 9.1 mAcm-2 . Our results revealed the possibility of improving both Voc and Jsc of the Cu2O homojunction by introducing a ZnO buffer layer.Item Electrodeposited homojunction Cu2O solar cell on FTO substrate(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Kafi, F. S. B.; Jayathilaka, K. M. D. C.; Wijesundera, L. B. D. R. P.; Siripala, W.Cuprous oxide (Cu2O), an abundant photoactive semiconducting material has optimum optoelectronic properties to develop efficient, inexpensive and eco-friendly solar cells. Even though, it is possible to fabricate Cu2O based hetero or Schottky junction solar cells, it is believed that the reduction of interface strains via application of surface treatments can produce best efficient homojunction Cu2O solar cell. Apart from the homogeneity of a p-n junction, reduction of contact resistances of a solar cell also has a great impact on its overall performance. Previous studies have shown that, annealing and/or sulphidation of thin film Cu2O enhances the surface properties while sulphided p-Cu2O/Au junction exhibits ohmic behavior as well. Thus, in this study possibility of developing efficient thin film homojunction Cu2O solar cell on FTO substrate was tested by improving the surface properties of n- and p-Cu2O thin film layers. n-Cu2O thin film was potentiostatically electrodeposited in a three electrode photoelectrochemical cell, contained 0.1 M sodium acetate and 0.01 M cupric acetate, acetic acid at bath pH value of 6.1 and then, this thin film FTO/n-Cu2O photoelectrode was annealed at temperature of 4000C to form very thin p-Cu2O layer with lower surface defects. Subsequently, for a thicker absorber layer a thin film ptype Cu2O was electrodeposited on annealed FTO/n-Cu2O photoelectrode using a lactate bath, consisted 3 M lactic acid, 0.4 M copper(II) sulphate and 4 M sodium hydroxide at bath pH value of 13.0. Finally, to form ohmic back contact this bi-layer is directly exposed to ammonium sulphide vapor for 8s and sputtered thin film of Au on it. Photoresponses and modulated light induced current-voltage characterization of this final thin film Cu2O homojunction is given the highest VOC and JSC values of 154 mV and 3.905 mA/cm-2 respectively. This result revealed that application of surface treatments to the thin film n-Cu2O and the bi-layers ameliorates surface properties, thereby the optoelectronic properties. Parameterization of surface treatments and improvements in the front contact will further improve this homojunction solar cell.Item Growth of photoactive Cu2ZnSnS4 by single step electrodeposition(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Fernando, W. T. R. S.; Jayathileka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.Cu2ZnSnS4 (CZTS) is a promising candidate for application in low-cost and environmentally-friendly thin film solar cells due to its optoelectronics properties. It is a perfect absorber material for photovoltaic applications due to its high absorption coefficient (>10-4 cm-1) and direct optical bandgap (1.4 - 1.5 eV). Among the CZTS preparation techniques, single step electrodeposition is an attractive because of its simplicity, low cost and easy to control stoichiometry. In this study, CZTS thin films on Mo substrate were potentiostatically electrodeposited in a three electrode electrochemical cell containing 0.02 M copper (II) sulfate pentahydrate (CuSO4·5H2O), 0.01 M zinc sulfate heptahydrate (ZnSO4·7H2O), 0.02 M tin sulfate (SnSO4) and 0.02 M sodium thiosulfate (Na2S2O3) at room temperature. 0.2 M tri-sodium citrate (C6H5Na3O7:Na3-citrate) was used as complexing agent and tartaric acid (C4H6O6) was used as pH control solution. pH of the bath was maintained at 5.0 Ag/AgCl and platinum electrodes were used as reference and counter electrodes respectively. Mo substrate with a deposition area of 1×2 cm2 was used as the working electrode. Electrodeposition was carried out at -1.05 V vs Ag/AgCl using a Hokuto Denko model HZ-5000 Potentiostat/Galvanostat. CZTS samples were prepared using different deposition durations (5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 min). Optimum bath conditions were explored using cyclic voltammetry. Samples were characterized using XRD, optical absorption, dark and light I-V measurements and spectral response measurements in a PEC containing 0.1 M sodium acetate. XRD measurements evidenced that the formation of single phase polycrystalline CZTS. Reflectance measurements has revealed that the band gap energy of the films is 1.5 eV and I-V measurements revealed that CZTS thin films were photoactive and p-type. To enhance the photoactive properties films were annealed at different temperatures (500, 550, 6000C) and durations (15, 30, 45 min) in H2S surrounding. As the results, photoactive performance of the films enhance with the annealing treatment in H2S. In conclusion, it can be mentioned that the highest photoactive p-CZTS thin films can be grown by annealing the 40 min deposited samples at 5500C for 30 min in H2S. The methodology developed in this study will be further investigated, in order to develop the material for wider applications.Item Optimization of growth parameters of photoactive Cu2ZnSnS4.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Fernando, W. T. R. S.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.Cu2ZnSnS4 (CZTS) is a promising candidate for application in low-cost and environmentally friendly thin film solar cells due to its optoelectronics properties. It is a perfect absorber material for photovoltaic applications due to its high absorption coefficient (>10-4 cm-1) and direct optical band gap (1.4 - 1.5 eV). Among the CZTS preparation techniques, electrodeposition of Cu, Sn and Zn stack layers followed by sulphurisation in H2S is an attractive technique because of its simplicity, low cost and easy to control stoichiometry. In this investigation, optimization of growth parameters in order to obtain photoactive CZTS thin films by sulphurisation of electrodeposited Cu, Sn and Zn stack layers has been investigated. Cu thin film was electrodeposited on Mo substrate at –0.89 V Vs Ag/AgCl electrode in an electrochemical cell containing 0.4 M CuSO4, 3 M lactic acid and NaOH at pH 11. Deposition of Sn thin film on Mo/Cu electrode was carried out at -1.2 V Vs Ag/AgCl in an electrochemical cell containing 0.055 M, 2.25 M NaOH and 8 ml of sorbitol. Zn thin film was electrodeposited on Mo/Cu/Sn at -1.2 V Vs Ag/AgCl in an electrochemical cell containing 0.2 M ZnSO4. Deposition parameters of Cu, Sn and Zn have been obtained by voltammograms. In order to grow CZTS, Mo/Cu/Sn/Zn thin film electrodes were annealed at 550 oC for 60 min in H2S. Sulphurisation process was carried out at different temperatures and durations using set of identical Mo/Cu/Sn/Zn thin film electrodes and thereby optimized temperature and duration of the sulpurisation. Atomic ratios of initial Cu, Sn and Zn layers could be crucial parameters in determining properties of CZTS thin films. Therefore, atomic ratios of Cu/Sn/Zn layers were optimized by changing Cu, Sn and Zn deposition duration. Various combinations of deposition durations were carried out and optimized by monitoring the dark and light I-V measurements in a PEC containing 0.1 M sodium acetate. Dark and light I-V characteristics revealed that the best photoactive CZTS films can be grown by depositing Cu for 20 min, Sn for 10 sec and Zn for 10 sec. Results further showed that photoconductivity of CZTS thin films is p-type. It is evident from reflectance measurements that the band gap of the CZTS films is 1.5 eV. In conclusion, it is found that the highest photoactive p-CZTS thin films can be grown by sulphurisation of electrodeposited Cu, Sn and Zn stack layers on Mo substrate using H2S at 550 oC for 60 min. Cu: Sn: Zn ratios of the stack layers are the crucial parameters in determining photoactive CZTS thin films. The methodology developed in this study will be further investigated in order to develop the materials for wider applications.Item Photoelectrolysis of water using electrodeposited Cu2O electrodes.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Silva, A. G. T. D.; Jayathilaka, K. M. D. C.; Wijesundera, R. P.; Siripala, W.At present, fossil fuels are the main energy contributor of the world’s energy needs but gradually depletion of fossil fuels is heading towards an energy crisis. Therefore it is very important for us to find out a renewable clean energy source to minimize the use of fossil fuels and environmental problems created by the burning fossil fuels. Among the suggested alternative fuels, hydrogen is one of the best and it can be produced by photoelectrolysis of water. Finding correct semiconducting materials and techniques are the key areas of research in the development of an efficient photoelectrolysis device. Ultra low cost electrodeposited cuprous oxide (Cu2O) is a good candidate material because it has required semiconductor properties for the process. p-Cu2O electrode electrolyte system requires external bias to produce photocurrent and this can be overcome by using n-Cu2O. However, in our previous studies, we have observed the possibility of enhancement of photocurrent at zero bias using double electrode system (electrodeposted n-Cu2O, thermally grown p-Cu2O, electrolyte system). In this investigation it was studied the possibility of photoelectrolysis of water using electrodeposited n- and p-Cu2O thin film electrodes as a double photoelectrode system in a 0.1 M sodium acetate photoelectrochemcal cell. n-Cu2O thin films on Ti substrates were potentiostatically electrodeposited at −200 mV Vs Ag/AgCl for 60 minutes in an aqueous solution containing 0.1 M sodium acetate and 0.01 M cupric acetate. The initial pH of the deposition bath was adjusted to 6.1. The temperature of the electrolyte was maintained at 55 °C and counter and reference electrodes were a platinum plate and a Ag/AgCl electrode, respectively. p-Cu2O thin films were electrodeposited on Ti substrate at -400 mV Vs Ag/AgCl for 40 min in a three-electrode electrochemical cell containing a 3 M sodium lactate and 0.4 M CuSO4 solution at pH 11. During the electrodeposition, the baths were continuously stirred using a magnetic stirrer. Prior to the film deposition, substrates were cleaned with detergent, dilute HCl, distilled water, and finally ultrasonicated in distilled water. Electrolytic solutions were prepared with distilled water and reagent-grade chemicals. n-Cu2O thin films are annealed at 150 oC for 10 min in air. Possibility of photoelectolysis using electrodeposited Cu2O has been investigated using dark and light current–voltage measurements in a three-electrode electrochemical cell containing 0.1 M aqueous sodium acetate solution. Results reveal that photoelectrolysis process is enhanced by 380% when n- and p-Cu2O double electrode system was operated compared to the n-Cu2O single electrode system.Item Fabrication of Cu2O homojunction thin films for photovoltaic applications.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Kafi, F. S. B.; Jayathilaka, K.M.D.C.; Wijesundera, R. P.; Siripala, W.Environmentally friendly cuprous oxide (Cu2O) is an attractive cost effective material for developing photovoltaic devices due to its astounding properties. Interestingly, the fabrication of low cost Cu2O homojunction devices is possible due to Cu2O is abundant and the ability of forming the p-Cu2O and n-Cu2O thin films using cost effective electrodeposition technique. Indeed, it is necessary to optimize p-n junction devices by varying deposition parameters. Vividly, the pH of the deposition bath controls the quality of the electrodeposited Cu2O thin films. Hence, it is important to optimize the pH value of the bath use for the electrodeposition of n-Cu2O and p-Cu2O films for developing Cu2O based devices. In this study, Cu2O thin film homojunction device was fabricated using a successive deposition of an n-Cu2O film followed by a p-Cu2O film, in two different baths; acetate and lactate respectively. The Cu2O homojunction was fabricated on a Ti substrate by the two-step potentiostatic electrodeposition process. A set of n-Cu2O thin films were electrodeposited on Ti substrate in a three electrode aqueous electrochemical cell containing 0.1 M sodium acetate and 0.01 M cupric acetate at potential of -200 mV vs. Ag/AgCl electrode, bath temperature of 55 °C and the film deposition time of 1 hour at two different pH values of n-Cu2O thin film deposition baths; 6.1 and 6.5. Then to optimize the Cu2O homojunction, Ti/n-Cu2O/p-Cu2O junction was fabricated by consequently electrodepositing p-Cu2O thin film on n-Cu2O film by changing the pH value from 7.0 to 13 of the p-Cu2O thin film deposition bath. The electrochemical bath used for the deposition of p-Cu2O thin films contained 3 M lactic acid, 0.4 M copper sulfate and 4 M NaOH. pH of the deposition baths were controlled by adding NaOH and HCl. Then Ti/n-Cu2O/p-Cu2O/Au structure was fabricated by sputtering Au on the resulted Cu2O homojunction. The highest photoactive film observed for Ti/n-Cu2O/p-Cu2O/Au structure that was fabricated at pH values of 6.1 and 11.0 for n-Cu2O and p-Cu2O deposition baths respectively. The observed VOC and JSC values for the optimum Ti/n-Cu2O/p-Cu2O/Au structure was 344 mV and 1.13 mA/cm2 respectively, under AM 1.5 illumination. The resulted high VOC and ISC values evident for the possibility of fabrication of Cu2O homojunction devices by employing consecutive electrodeposition of an n-Cu2O layer followed by a p-Cu2O layer using the relevant baths at different growth conditions. Promisingly, fabricated Cu2O homojunction may further improved by surface treatments and optimizations, to produce high efficient Cu2O homojunction devices.