Wilman Septina

In this study, a novel sequential electrodeposition of Cu-Zn-Sn-Se and Cu-Sn-Se layers was applied for fabrication of a Cu2ZnSnSe4 (CZTSe) thin film. The desired Cu-Zn-Sn-Se/Cu-Sn-Se bilayer was obtained at a selected applied potential from electrolytes containing corresponding metal and selenium ions. Annealing of the bilayer film under argon (Ar) flow induced significant losses of Sn and Se components due probably to evaporation of the SnSe compound. Suppression of these losses could be realized by introduction of Se vapor during the annealing: as a result, a CZTSe thin film with an ideal Cu-poor/Zn-rich composition for solar cell application was obtained. The solar cell with a device with the structure of glass/Mo/CZTSe/CdS/ZnO/AZO derived from thus-obtained CZTSe film exhibited a conversion efficiency of 1.1%, while the device still possessed a significant leakage current and a high series resistance.

Polycrystalline CuInS2 chalcopyrite thin films were formed on a Mo-coated glass substrate by annealing of spray deposited precursor films in a sulfur atmosphere. Structural and photoelectrochemical analyses of CuInS2 films obtained by annealing at 500 °C and 600 °C revealed that a well-defined crystalline film was obtained by the 600 °C annealing. Owing to these favorable properties, the solar cell with an Al:ZnO/CdS/CIS/Mo/glass structure based on the 600 °C annealed CuInS2 film showed higher conversion efficiency than that obtained on the cell derived from the 500 °C annealed CuInS2. Partial incorporation of Ga in the CuInS2 film with a Ga/In ratio of ca. 0.2 to form a Cu(In,Ga)S2 mixed crystal without any reduction of photoelectrochemical properties can be achieved by introduction of a Ga source in the sprayed solution. As a result, the solar cell based on the 600 °C annealed Cu(In,Ga)S2 film showed the best conversion efficiency (5.8%) of the present sprayed chalcopyrite films. By introduction of a CdS thin layer followed by loading Pt deposits, moreover, the 600 °C annealed Cu(In,Ga)S2 film worked as a photocathode for photoelectrochemical water splitting with applied bias potential of >0.65 V.

Single-step electrodeposition synthesis of a Cu2ZnSnSe4 (CZTSe) film on a Mo-coated glass substrate from an acidic electrolyte containing Cu(II), Zn(II), Sn(IV), and Se(IV) species was investigated. The desired CZTSe film as the main phase was obtained at some selected applied potential ranges through reaction among binary selenides, Cu2Se, ZnSe and SnSe2, which were continuously formed in the present electrolyte containing all of the elements. Sulfurization of the as-deposited film at several temperatures under H2S gas flow resulted in the formation of corresponding mixed compounds of CZTSe and Cu2ZnSnS4 (CZTS), i.e., Cu2ZnSn(S,Se)4 (CZTSSe): specifically, sulfurization at temperatures higher than 500 °C resulted in the formation of single-phase CZTSSe with S-rich compositions. By analyzing linear sweep voltammograms (LSVs) of sulfurized films under chopped irradiation, the films were confirmed to have p-type photoresponses; the film obtained by 500 °C sulfurization showed the largest photoresponse because of its sufficiently large grain size and less voids, whereas the presence of an anodic spike in the LSV curve as well as the observation of a broad external quantum efficiency (EQE) spectrum suggested the requirement of further improvement in film quality for photovoltaic application.

An approach to fabricate crystalline kesterites films of CZTSSe, CZTS, and CZTSe by annealing a single-step electrodeposited Cu-Zn-Sn-Se precursor film under various conditions was reported. Successful formations of the kesterite films were confirmed by XRD and Raman analysis. EDX results revealed that annealing at relatively high temperatures resulted in improved atomic compositions of CZTSSe, CZTS, and CZTSe films closer to the ideal stoichiometry. Based on the photoelectrochemical measurement, all of the kesterites films thus-obtained exhibited p-type semiconductor photoresponses. Specifically, the CZTS sample, which was obtained by annealing under H2S atmosphere, showed a highest photocurrent because of the formation of relatively bigger grain and denser structure.

Cu2ZnSn(S,Se)4 thin film has been fabricated by sulfurization of a novel single-step electrodeposited Cu-Zn-Sn-Se precursor. Based on EDX analysis of the precursor film, the atomic percentages of Cu, Zn, Sn and Se measured to be 38.48%, 11.53%, 13.62% and 36.37%, respectively. The A1 Raman mode of Cu2ZnSnSe4 was detected from the film which suggests the formation of the quaternary compound during the deposition. Annealing of the precursor film at 550°C under H2S-gas flow resulted in the formation of crystalline Cu2ZnSn(S,Se)4 compound. Photoelectrochemical measurement of the film revealed that the Cu2ZnSn(S,Se)4 thus-obtained had a p-type semiconductor photoresponse with the band gap energy of 1.48 eV.

Electrochemical deposition of indium (In) on a copper-covered molybdenum-coated glass substrate from several acidic InCl3 solutions was studied for fabrication of CuInS2-based solar cells. When In was deposited using a simple acidic InCl3 solution at −0.80 V (vs. Ag/AgCl), island-shaped growth was observed, whereas a homogeneous In film was obtained from InCl3 solution containing citric acid and sodium citrate at −0.98 V (vs. Ag/AgCl). Electrochemical and structural analyses revealed that the citric acid additive had a function for smoothing the surface of the In deposit. The mixing with sodium citrate induced appreciable inhibition of H2 evolution during the In deposition, leading to high current efficiency of >90%. The CuInS2 film derived from the homogeneous In had a uniform thickness with a smooth surface, while the CuInS2 film obtained from the island-shaped In deposit showed a large variation in thickness with recessed areas. The CuInS2 film derived from the homogeneous In was showed better photoelectrochemical response than that of the film fabricated from the island-shaped In. As expected from these differences, the solar cell with an Al:ZnO/CdS/CuInS2/Mo structure derived from the homogeneous In film showed the best conversion efficiency of 7.8% with relatively high reproducibility.

We fabricated inorganic/organic hybrid solar cells consisting of a p-type Cu2O layer and a fullerene derivative (PCBM) layer, which were prepared by wet processes. The Cu2O layer was grown by electrochemical deposition from an alkaline solution (pH 12.5) containing copper (II) sulfate and lactic acid. A PCBM layer was deposited on it by spin-casting a solution of PCBM. The optimized solar cell showed short circuit current density of 1.5 mA/cm2, open circuit voltage of 0.4 V, and overall power conversion efficiency of 0.095% under the condition of AM 1.5 G (100 mW/cm2). Improvement in mobility and lifetime of electrons in the Cu2O layer is considered to be the key to increase efficiency further.

Recently, compound semiconductor thin-film solar cells based on chalcopyrite analogues are beginning to penetrate the market. These films are usually prepared by vacuum techniques, such as coevaporation of elements, sequential sputtering of thin layers of elements followed by selenization and/or sulfurization. However, the use of such vacuum techniques often leads to high equipment costs and significant losses of raw materials. Electrochemical deposition is an attractive non-vacuum method for fabrication of these chalcogenide-based solar cells ...

"Potentiostatic deposition of Cu2O thin films on glass substrates coated with F-doped SnO2 from an alkaline electrolyte solution (pH 12.5) containing copper (II) sulfate and lactic acid was studied for fabrication of a Cu2O/Al-doped ZnO (AZO) heterojunction solar cell. The band gap of the electrodeposited Cu2O films was determined by photoelectrochemical measurements to be around 1.9 eV irrespective of the applied potentials. The solar cells with a glass/FTO/Cu2O/AZO structure were fabricated by sputtering an AZO film onto the Cu2O film followed by deposition of an Al contact by vacuum evaporation. The highest efficiency of 0.603% was obtained with a Cu2O film deposited at -0.6 V (vs. Ag/AgCl). This was attributed to better compactness and purity of the Cu2O film than those of the Cu2O films deposited at other potentials.

Key Words: electrodeposition, Cu2O, potentiostatic regime, Al-doped ZnO, heterojunction"

Electrochemical deposition of Cu2O layers on an FTO glass substrate from an alkaline electrolyte solution containing copper sulfate and lactic acid was studied for fabrication of a Cu2O/Al-doped ZnO (AZO) heterojunction solar cell. Structural characterizations of Cu2O layers by using scanning electron microscope, UV-Visible absorption, X-ray diffraction, and X-ray photoelectron spectra revealed that compactness, flatness, Cu2O grain sizes, and compositions of Cu2O films were strongly influenced by applied potentials for the electrodeposition. The performance of the solar cells with a FTO/Cu2O/AZO/Al structure, which was fabricated by sputtering an AZO film onto the Cu2O films followed by deposition of an Al back contact by vacuum evaporation, was highest when the Cu2O film deposited at -0.6 V (vs. Ag/AgCl) with photovoltaic conversion efficiency of 0.6 %, open circuit voltage of 0.29 V, short-circuit current density of 7.12 mA/cm2, and a fill factor of 0.292. Relatively high compactness and flatness of the Cu2O film compared to those obtained at different potentials led to the better photovoltaic performance. Subsequent heat treatment of the highest conversion efficiency cell at 150°C degrades the photovoltaic properties which was mainly caused by the decrease of Cu2O crystallinity.

Nanoporous mesostructure TiO2 powders were synthesized by sol-gel method, with TiCl4 as a precursor in methanol solution. The Pluronic PE 6200 of block copolymer was used as the pores template. It was found from XRD measurements, both at 400oC and 450oC calcination temperatures, the sol-gel technique yielded the nanoporous TiO2 with anatase phase. Based on N2 adsorption characterization using BET method, the TiO2 samples have surface area of 108 m2/g and 88 m2/g for calcination temperatures of 400oC and 450oC of, respectively. From small-angle neutron scattering (SANS) patterns, TiO2 samples were observed to have nanoporous structures with pore sizes between 22-24 nm. The TiO2 also have order degree which depends on the calcination temperature. The potential applicability of the resulting TiO2 is confirmed for dye-sensitized solar cell (DSSC), composed of nanoporous anatase TiO2 and natural dye from antocyanine black rice. UV-Vis measurement of dye extracted from the black rice indicated that the antocyanin chelate can propagate into the TiO2 nanoporous network. The short circuit photocurrent density (Jsc) under 100 mWcm-2 reached 1.287 mAcm-2 with open circuit photovoltage (Voc) of 550 mV and the fill factor of 39.12%. The results show that the hybrid organic-inorganic structures are very attractive for future low cost devices.

Titanium dioxide (TiO2) is one of the most studied metal oxide especially in its application for energy and environment areas. TiO2 is well known as a main semiconductor oxide in dye-sensitized solar cell (DSSC) as well as a photocatalyst material for pollutant decomposition. For those applications, TiO2 is necesarry to exhibit high surface area. Mesoporous material (2-50 nm in pore size), with its high surface area, homogenous pore
distributions, dan ordered pores characteristics, is ideal structure for those TiO2 applications.
In this research, nanocrystal mesoporous TiO2 powder was synthesized using sol-gel method, with TiCl4 as a precursor in methanol/ethanol solution. Block copolymer Pluronic PE 6200 and Pluronic PE 8100 were used as a pores template to form mesoporous structure. From XRD result, it is shown that 400oC and 450oC calcination temperature resulted in nanocrystal TiO2 with anatase phase for methanol solvent, and bicrystal anatase-rutile phase for ethanol solvent on low relative humidity condition. Based on N2 adsorption characterization (BET method), generally TiO2 samples have high surface area compared
to commercialized nano-TiO2 about 80-108 m2/g. From Small-angle Neutron Scattering (SANS) patterns, it is shown that TiO2 samples using block copolymer Pluronic PE 6200 have mesoporous structure which is the pore ordering degree depend on calcination temperature.

Keywords
Titanium dioxide (TiO2), mesoporous material, sol-gel method, block copolymer, SANS,
nanocrystal

"Konversi energi surya menjadi energi listrik merupakan solusi yang ideal untuk menghasilkan energi yang bersih dan murah. Namun sekarang ini harga sel surya silikon, sel surya yang mendominasi pasar, masih relatif mahal dan membutuhkan teknologi yang tinggi dan proses produksi yang sulit. Dye-sensitized solar cell (DSSC), sebagai teknologi sel surya yang berkembang karena kebutuhan akan sel surya berefisiensi tinggi dan proses produksinya yang simpel, merupakan alternatif sel surya murah dimasa yang akan datang. Dye-sensitized solar cell merupakan sel surya yang berbasis fotoelektrokimia dimana proses absorbsi cahaya dilakkan oleh molekul dye dan proses separasi muatan oleh bahan inorganik semikonduktor TiO2.
Pada peneltian ini telah berhasil dilakukan pembuatan prototipe dye-sensitized solar cell dengan menggunakan dye bahan organik jenis anthocyanin dye dari ekstraksi buah delima, dan semikonduktor nanopori TiO2 yang disintesis dengan menggunakan metoda sol-gel dengan bantuan block copolymer sebagai template pori. Dari hasil pengujian struktur nanopori TiO2 didapat bahwa TiO2 yang disintesis cocok untuk diaplikasikan dalam DSSC karena mempunyai luas permukaan yang tinggi dan kristalinitas yang baik, dan dari pengujian absorbsi cahaya dye ekstraksi buah delima diketahui bahwa dye dapat menyerap spektrum cahaya pada panjang gelombang 562 nm. Selain itu ketika sel surya disinari dengan cahaya matahari, sel surya dapat mengkonversi energi surya menjadi energi listrik dengan tegangan 162,4 mV dan arus listrik sebesar 0,07 mA untuk area aktif seluas 0.6 cm2."