Wilman Septina

Platinum and indium sulfide-modified CuInS2 as efficient photocathodes for photoelectrochemical water splitting

A highly efficient CuInS2-based photocathode for water reduction with a maximum applied bias photon-to-current efficiency of ca. 2% was prepared by using a novel In2S3 surface modifier.

Fabrication of CuInS2 and Cu(In,Ga)S2 thin films by a facile spray pyrolysis and their photovoltaic and photoelectrochemical properties

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.

Selective production of CuSbS2, Cu3SbS3, and Cu3SbS4 nanoparticles using a hot injection protocol

Homogeneous Cu–Sb–S nanocrystals with several compositions can be synthesized in a solution through the hot-injection method. Photoelectrochemical analyses of films of these nanoparticles revealed that these nanoparticles have p-type semiconductive characters.

Cu(In,Ga)(S,Se)2 Thin Film Solar Cell with 10.7% Conversion Efficiency Obtained by Selenization of the Na-Doped Spray-Pyrolyzed Sulfide Precursor Film

Selenium-rich Cu(In,Ga)(S,Se)2 (CIGSSe) thin films on an Mo-coated soda-lime glass substrate were fabricated by spray pyrolysis of an aqueous precursor solution containing Cu(NO3)2, In(NO3)3, Ga(NO3)3, and thiourea followed by selenization at 560 °C for 10 min. We studied the effects of intentional sodium addition on the structural and morphological properties of the fabricated CIGSSe films by dissolving NaNO3 in the aqueous precursor solution. The addition of sodium was found to affect the morphology of the final CIGSSe film: the film had denser morphology than that of the CIGSSe film obtained without addition of NaNO3. Photoelectrochemical measurements also revealed that the acceptor density of the nondoped CIGSSe film was relatively high (N(a) = 7.2 × 10(17) cm(-3)) and the addition of sodium led to a more favorable value for solar cell application (N(a) = 1.8 × 10(17) cm(-3)). As a result, a solar cell based on the sodium-modified CIGSSe film exhibited maximum conversion efficiency of 8.8%, which was significantly higher than that of the cell based on nondoped CIGSSe (4.4%). In addition, by applying MgF2 antireflection coating to the device, the maximum efficiency was further improved to 10.7%.

Cu2ZnSnS4 thin film solar cells with 5.8% conversion efficiency obtained by a facile spray pyrolysis technique

An attempt was made to fabricate Cu2ZnSnS4 (CZTS) thin film absorber on a Mo-coated glass substrate by using facile spray pyrolysis deposition of a precursor film from an aqueous solution containing Cu(NO3)2, Zn(NO3)2, Sn(CH3SO3)2 and thiourea. In order to obtain a stable solution for the spray pyrolysis deposition without formation of an SnO2 precipitate, the mixing order of source materials was found to be important. Annealing of the thus-obtained precursor film in sulfur vapor at temperatures ranging from 580 °C to 600 °C resulted in successful formation of homogeneous films composed of CZTS crystallites. Based on structural analyses of CZTS films having different Sn contents, an Sn-rich composition compared to its stoichiometric amount was found to be essential for efficient grain growth of the resulting CZTS films. A solar cell based on the Sn-rich CZTS film obtained by an optimum annealing condition exhibited maximum conversion efficiency of 5.8%.

Investigation of the Electric Structures of Heterointerfaces in Pt- and In2S3-Modified CuInS2 Photocathodes Used for Sunlight-Induced Hydrogen Evolution

Copper indium disulfide (CuInS2) modified with an In2S3 layer and a Pt catalyst showed a more efficient photoelectrochemical (PEC) property for hydrogen evolution from a nearly neutral (pH 6) 0.2 M NaH2PO4 solution under simulated sunlight illumination (AM 1.5G) than that of a CuInS2 electrode modified with a CdS layer and a Pt catalyst. Analysis of the PEC properties of In2S3-modified CuInS2 (In2S3/CuInS2) and CdS-modified CuInS2 (CdS/CuInS2) in solutions containing an electron scavenger (Eu(3+)) showed identical enhancement of the PEC properties of In2S3/CuInS2 when compared to those of CdS/CuInS2, indicating the formation of a favorable heterointerface in In2S3/CuInS2 for efficient charge separation. Spectroscopic evaluation of conduction band offsets revealed that In2S3/CuInS2 had a notch-type conduction band offset, whereas a cliff-type offset was formed in CdS/CuInS2: these results also revealed a better interface electric structure of In2S3/CuInS2 than that of CdS/CuInS2.

Electrochemical synthesis of Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 thin films for solar cells

Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) thin films were fabricated by successive electrodeposition of layers of precursor elements followed by sulfurization and selenization of an electrodeposited Cu-Zn-Sn-Se precursor. It is known that the Sn layer tends to have an island-shaped morphology, leading to formation of inhomogeneous CZTS films with rough surface. In order to improve qualities of the CZTS film, we tried to optimize the deposition condition of Sn layers. As a result, we were able to deposit Sn layers with improved morphologies. A CZTS solar cell fabricated using the Sn layer showed energy conversion efficiency of 4.4%. We also fabricated CZTSe films using Cu-Zn-Sn-Se films made by one-step electrochemical deposition as the precursor films. These films were converted into CZTS films by anneling in Ar. However, the annealing induced significant losses of Sn and Se components. These losses could be suppressed by introduction of Se vapor into the Ar atmosphere. The solar cells based on CZTSe films prepared by these methods exhibited appreciable properties.

Fabrication of Cu(In,Ga)(S,Se)2 thin film solar cells via spray pyrolysis of thiourea and 1-methylthiourea-based aqueous precursor solution

A detailed process of fabricating Cu(In,Ga)(S,Se)2 via the spray pyrolysis of a thiourea-based precursor solution followed by selenization is reported. The optimization of the selenization condition for the fabrication of the Cu(In,Ga)(S,Se)2 film led to a conversion efficiency of 7.8% for the Cu(In,Ga)(S,Se)2-based device. We also showed that 1-methylthiourea was a more suitable sulfur source for the spray pyrolysis technique, resulting in a conversion efficiency of 8.7% (VOC = 0.52 V, JSC = 31 mA cm−2, and FF = 0.54) without any antireflection coating.

Photoelectrochemical Characterizations of CuInS2 and Cu(In,Ga)S2 Thin Films Fabricated by a Spray Pyrolysis Method

Polycrystalline CuInS2 chalcopyrite thin films were formed on a Mocoated glass substrate by annealing of a spray deposited precursor film in a sulfur atmosphere at 600 °C. 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 was also prepared. Photoelectrochemical (PEC) analyses revealed that the Ga incorporation was effective to modulate electric and semiconductive properties of the chalcopyrite film. As a result, relatively large cathodic photocurrent responses in PEC analyses as well as high photovoltaic properties of a solar cell based on the Cu (In,Ga)S2 film were obtained.

CuSbS 2 -based thin film solar cells prepared from electrodeposited metallic stacks composed of Cu and Sb layers

Polycrystalline copper antimony sulfide (CuSbS2) films were fabricated by sulfurization of electrodeposited metallic stacks of Cu and Sb layers with various Cu/Sb atomic ratios at 450 °C in H2S (5% in Ar). Structural analyses using X-ray diffraction revealed that CuSbS2 films obtained from Cu-poor and Cu-rich metallic stacks (Cu/Sb = 0.7 and 1.3) contained impurity phases, whereas single-phase CuSbS2 film was formed from the stoichiometric stack (Cu/Sb = 1). Morphological studies using SEM indicated that adherence of thus-formed CuSbS2 films to the Mo substrate was dependent on the precursor composition: a CuSbS2 film with poor adherence having many crevices was formed when the Cu-rich metallic stack was used, while CuSbS2 films with good adherences were obtained when Cu-poor and stoichiometric metallic stacks were used. Performance of solar cells with an Al:ZnO/CdS/CuSbS2/Mo structure also depended on structural characteristics of these CuSbS2 films, i.e., a preliminary conversion efficiency of ca. 3% was obtained for device based on the CuSbS2 film obtained from the stoichiometric metallic stack, whereas the devices derived from Cu-poor and Cu-rich metallic stacks showed the conversion efficiency less than 1%.