CuInS2 Layer Research Articles

Solution processed CuInS2/SnO2 heterojunction based self-powered photodetector for UV encrypted visible light communication

A photodetector (PD) featuring dual-band detection capability and self-powering attributes is crucial for various applications in sensing, communication, and imaging. Here, we present a self-powered PD based on a solution-processed CuInS2/SnO2 heterojunction capable of detecting ultraviolet (UV) and visible light spectra. The CuInS2 layer was composed of ∼2 nm-sized quantum dots (QDs) synthesized using the hot injection method, while the SnO2 layer was fabricated using a straightforward sol-gel technique. This self-powered PD displayed a significant spectral response across both UV (355 nm) and visible light (532 nm) ranges, all accomplished without the need for external bias. The PD demonstrates rapid detection, with rise and decay times of 125 ms and 156ms for visible light and 85 ms and 200 ms for UV light, respectively, at a power level of 15 mW. The PD achieved responsivity values of 10.66 μA/W and 34.56 μA/W for visible and UV light, respectively. The impressive capability for dual-band detection in both ultraviolet (UV) and visible light showcases the practical feasibility and utility of this device for self-powered photodetection and deciphering UV-encrypted visible light communication. Moreover, its straightforward solution-based processing attribute renders it valuable for the mass production of devices and technology.

Postdeposition Sulfurization of CuInSe2 Solar Absorbers by Employing Sacrificial CuInS2 Precursor Layers

Herein, a new route of sulfur grading in CuInSe2 (CISe) thin‐film solar absorbers by introducing an ultrathin (<50 nm) sacrificial sputtered CuInS2 (CIS) layer on top of the CISe. Different CIS top layer compositions (Cu‐poor to Cu‐rich) are analyzed, before and after a high‐temperature treatment in selenium (Se)‐ or selenium+sulfur (SeS)‐rich atmospheres. An [S]/([S] + [Se]) grading from the surface into the bulk of the Se‐ and SeS‐treated samples is observed, and evidence of the formation of a mixed CuIn(S,Se)2 phase by Raman analysis and X‐ray diffraction is provided. The optical bandgap from quantum efficiency measurements of solar cells is increased from 1.00 eV for the CISe reference to 1.14 and 1.30 eV for the Se‐ and SeS‐treated bilayer samples, respectively. A ≈150 mV higher VOC is observed for the SeS‐treated bilayer sample, but the cell exhibits blocking characteristics resulting in lower efficiency as compared with the CISe reference. This blocking is attributed to an internal electron barrier at the interface to the sulfur‐rich surface layer. The difference in reaction routes and possible ways to improve the developed sulfurization process are discussed.

Effect of Cu Content on Post‐Sulfurization of Cu(In,Ga)Se2 Films and Corresponding Solar Cell Performance

Herein, the effect of the initial copper content of co‐evaporated Cu(In1−x,Gax)Se2 (CIGS) absorber films on the impact of a post‐annealing step in elemental sulfur atmosphere is studied. The Cu concentration is varied over a wide range ([Cu]/[III] = CGI = 0.57–1.23), allowing to identify composition‐dependent trends in phase formation, chemical rearrangements, and solar cell performance after sulfurization. For all samples, a ternary CuInS2 layer forms at the surface. In addition, sulfur 1) is incorporated in randomly distributed CuIn(S,Se)2 mixed crystals underneath CuInS2; 2) diffuses into multidimensional defects (e.g., dislocations and grain boundaries); and 3) is bound in Na–In–S surface plates. It is found that Cu‐poor absorber composition (CGI ≤ 0.82) favors CuInS2 growth as compared with close‐stoichiometric CIGS films, driven by a faster diffusion of Cu toward the surface. For Cu‐rich absorbers (CGI > 1), Se—S exchange is significantly accelerated, presumably by the presence of Cu2−xSe phases reacting to Cu2−xS and eventually catalyzing CuInS2 formation. Finally, open‐circuit voltage (VOC), fill factor (FF), and efficiency (η) of corresponding solar cells increase after sulfurization with increasing CGI until stoichiometry is reached. The result is explained by a mitigated Cu depletion of the absorber bulk after sulfurization for close‐stoichiometric CIGS.

Decoration of 3D ZnO nanoelectrodes with CuInS2 for solar water splitting

This study reports the decoration of zinc oxide (ZnO) nanosheets with copper indium sulfide (CuInS2) via sequential metal deposition and post sulfurization methods for photoelectrochemical solar cell application. The three dimensional (3D) ZnO nanosheets are hydrothermally grown on conductive glass substrates by chemical bath deposition. Then, copper/indium metallic alloy is deposited via magnetron sputtering and annealed at high temperature in the presence of elemental sulfur to form CuInS2 absorber on the surface of 3D nanosheets. Photoelectrochemical measurements indicate that the decoration of CuInS2 layer over the ZnO nanosheets results in significant increase in the photocurrent density to 28 mA cm−2 (at 0.5 V vs Ag/AgCl) leading a remarkable amount of hydrogen generation during solar water splitting process, 1387 μmol measured at 0 V vs Ag/AgCl under 1 sun-illumination for 4 h.

Photoelectrochemical Water Splitting of CuInS2 Photocathode Collaborative Modified with Separated Catalysts Based on Efficient Photogenerated Electron–Hole Separation

Accelerating the separation and transfer of photogenerated carriers of a photoelectrode is vital to achieve a substantial performance increase for the photoelectrochemical (PEC) water splitting. In this paper, a CuInS2 photocathode collaborative modified with separated cocatalyst layers including top Pt layer and bottom FeOOH layer is first fabricated to ameliorate PEC water splitting. The FeOOH layer can utilize holes from the CuInS2 layer and then transfer holes through the conductive glass and wire to the counter electrode. The Pt layer can collect and transfer electrons from the CuInS2 layer to the surface for water reduction. The collaborative FeOOH and Pt ameliorate effectively the hole and electron separation so as to improve PEC performances. An improved photocurrent density of ITO/FeOOH/CuInS2/Pt photocathode reaches −6.79 mA·cm–2 at −0.4 V vs RHE. Moreover, this study will be instructive for the design of efficient photocathode used in photoelectrochemical water splitting.

Challenges in TEM sample preparation of solvothermally grown CuInS2 films

Transmission electron microscopy (TEM) is a widely used tool to characterize materials. The required samples need to be electron transparent which should be achieved without changing the microstructure. This work describes different TEM sample preparation techniques of nanostructured CuInS2 thin films on fluorine-doped tin oxide substrates, synthesized solvothermally using l‐cysteine as sulfur source. Focused ion beam lamellae, conventional cross section samples and scratch samples have been prepared and investigated. It was possible to prepare appropriate samples with each technique, however, each technique brings with it certain advantages and disadvantages. FIB preparation of solvothermally synthesized CuInS2 suffers from two main drawbacks. First, the whole CuInS2 layer displays a strongly increased Cu content caused by Cu migration and preferential removal of In. Further, electron diffraction shows the formation of an additional CuS phase after Ga+ bombardment. Second, diffraction analysis is complicated by a strong contribution of crystalline Pt introduced during the FIB preparation and penetrating into the porous film surface. The conventional cross sectional CuInS2 sample also shows a Cu signal enhancement which is caused by contribution of the brass tube material used for embedding. Additionally, Cu particles have been observed inside the CuInS2 which have been sputtered on the film during preparation. Only the scratch samples allow an almost artefact-free and reliable elemental quantification using energy-dispersive X-ray spectroscopy. However, scratch samples suffer from the drawback that it is not possible to determine the layer thickness, which is possible for both cross sectional preparation techniques. Consequently, it is concluded that the type of sample preparation should be chosen dependent on the required information. A full characterization can only be achieved when the different techniques are combined.

Enhanced UV–Vis photocatalytic performance of the CuInS2/TiO2/SnO2 hetero-structure for air decontamination

Photoactive hetero-structures based on SnO2, TiO2 and CuInS2 were prepared by robotic spray pyrolysis with optimized deposition parameters. The samples containing metal oxides have uniform and homogeneous surfaces with granular morphologies. The insertion of a CuInS2 layer supports the development of aggregates with different shapes and sizes (0.1–1μm). The samples have a surface energy governed by the polar component, outlining the hydrophilic behaviour. According to their band gap, the metal oxides layers absorb mostly in the UV spectral region; by adding the narrow band gap CuInS2 there is a broadening of the spectral range towards Vis, from a maximum of 400nm (for the samples containing SnO2 and TiO2) up to 700nm. Additionally, the components of the photoactive hetero-structure have suitably positioned energy bands allowing improved charge carrier separation and mobility. Consequently, the samples show UV–Vis photocatalytic properties outlined in air decontamination, for acetaldehyde removal.

Fabrication of selenization-free superstrate-type CuInS2 solar cells based on all-spin-coated layers

Today manufacturing of high efficiency chalcogenide thin film solar cells is based on high cost vacuum-based deposition processes at high temperature (>500 °C) and in chalcogen -containing atmosphere. In this paper, we introduce a simple vacuum-free and selenization-free, solution processing for fabricating a superstrate-type CuInS2 (CIS) solar cell. The absorber, buffer and blocking layers were all deposited by spin coating of molecular precursor inks. We demonstrate the deposition of In2S3 buffer layer by sol-gel spin casting for the first time. The rapid sintering process of CIS layer was carried out at 250 °C that is considered a very low temperature in CIGS thin-film technologies. A novel molecular-ink route to deposit In2S3 type buffer layer is presented. For the back contact we employed carbon, deposited by simple knife coating method. Different parameters including type of buffer, thickness of absorber layer, CIS and In2S3 annealing temperature and morphology were optimized. Our air stable simple device structure consisting of <Glass/FTO/TiO2/In2S3/CIS/Carbon > showed promising power conversion efficiency (PCE) of 2.67%.

Conformal core-shell nanostructured photodetectors with enhanced photoresponsivity by high pressure sputter deposition

ABSTRACTWorking gas pressure during sputter deposition can significantly affect the conformality of a thin film when it is grown on a nanostructured surface. In this study, we fabricated core-shell nanostructured photodetectors, where n-type In2S3 nanorod arrays (core) were coated with p-type CuInS2 (CIS) films (shell) at relatively low and high Ar gas pressures. In2S3 nanorods were prepared by glancing angle deposition (GLAD) technique using a thermal evaporator unit. CIS films were deposited by RF sputtering at Ar pressures of 2.7x10-2 mbar (high pressure sputtering, HIPS) and 7.3x10-3 mbar (low pressure sputtering, LPS). The morphological characterization was carried out by means of SEM. The photocurrent measurement was conducted under 1.5 AM Sun under no bias. Nanostructured photodetectors of HIPS-CIS/GLAD-In2S3 (i.e. HIPS-GLAD) were shown to demonstrate enhanced photoresponse with a photocurrent value of 98 μA, which is about ∼230% higher than that of LPS-GLAD devices. The enhancement originates from the improved core-shell structure achieved by more conformal coating of the CIS shell. In addition, the results were compared to their counterpart thin-film devices incorporating an In2S3 film coated either with HIPS or LPS CIS layer. Nanorod devices with high and low pressure CIS films showed photocurrent values ∼20 times and ∼ 19 times higher compared to those of high and low pressure film devices, respectively. This finding can be explained by the higher light absorption property of nanorods, and the reduced inter-electrode distance as a result of core-shell structure, which allows the effective capture of the photo-generated carriers. Therefore, the results of this work can pave way to the development of high photoresponse core-shell semiconductor devices fabricated by physical vapor deposition techniques.

Fabrication of ETA cells based on ZnO/CuInS2 core/shell heterostructure

ZnO/CuInS2/CuSCN heterostructure was synthetised using ZnO/CuInS2 core/shell nanorods array as substrate via a low cost electrodeposition method. The as obtained heterostructure could be considered as the main part of typical extremely thin absorber solar cell, since the ZnO nanorods and CuInS2 layer would serve as the electronic delivery material and light absorber, while the β-CuSCN would play the role of hole conductor. The as obtained heterostructure shows a high absorbing capacity in the visible part of the solar spectrum with a light absorption centre located at ∼550 nm, and the efficiency of the solar cells was measured to be 0.16% using Au as counter electrode.

Impact of Cu–Au type domains in high current density CuInS2 solar cells

In this work, a series of stain steel 15×15cm2 CuInS2 solar cells with efficiencies close to the record one for this kind of devices, are analyzed. Through a careful and comprehensive study of the structural and electronic properties of the CuInS2 layer, we show that in a general fashion the strain originated by the thermal annealing affects the energy band splitting and reduces the short circuit current. Then, through an innovative combination of photoreflectance and Raman scattering analysis, we demonstrate that the presence of CuAu domains in the bulk layer of a CuInS2 is directly related with this strain reduction contributing to the improvement of short circuit current. We propose that the presence Cu–Au phase domains reduce the strain within the CuInS2 layer, and improve the quality of the CIS chalcopyrite crystals, leading to reduced carrier recombination while increasing carriers mobility. As a consequence we conclude that the presence of said domains improves the short circuit current in the studied devices.

Efficient perovskite solar cells based on low-temperature solution-processed (CH3NH3)PbI3 perovskite/CuInS2 planar heterojunctions.

In this work, the solution-processed CH3NH3PbI3 perovskite/copper indium disulfide (CuInS2) planar heterojunction solar cells with Al2O3 as a scaffold were fabricated at a temperature as low as 250°C for the first time, in which the indium tin oxide (ITO)-coated glass instead of the fluorine-doped tin oxide (FTO)-coated glass was used as the light-incidence electrode and the solution-processed CuInS2 layer was prepared to replace the commonly used TiO2 layer in previously reported perovskite-based solar cells. The influence of the thickness of the as-prepared CuInS2 film on the performance of the ITO/CuInS2(n)/Al2O3/(CH3NH3)PbI3/Ag cells was investigated. The ITO/CuInS2(2)/Al2O3/(CH3NH3)PbI3/Ag cell showed the best performance and achieved power conversion efficiency up to 5.30%.

CuInS2 solar cell absorber plasmonically modified by gold nanoparticles

Thin CuInS2 light-absorbing layer prospective for the solar cell applications is modified by gold nanoparticles. Theoretical and experimental possibilities of placement nanoparticles over or under the CuInS2 coating were tested. It was revealed that placement of nanoparticles under the CuInS2 layer is better in terms of spray pyrolysis technique. It results in more effective plasmon-enhanced light absorption in the CuInS2 layer at the visible/near infrared 650–700 nm spectral range.

Brush Plated Copper Indium Selenide Films and Their Characteristics

In recent years, there has been a growing attention to ternary chalcopyrite compound CuInSe2 (CIS) and its alloys with gallium CuIn x Ga1−x Se2 (CIGS) owing to their promising performance for thin film solar cell applications. The conversion efficiencies have already exceeded 19% using these materials at the laboratory scale. Over the past decades, CIS thin films have been successfully electrodeposited using direct current (d.c.) under the potentialstatic or galvanostatic condition, and periodic pulse electrodeposition technique. In this work, the brush plating technique has been employed for the first time to deposit CIS films.CIS films were deposited by the brush plating technique for the first time. Analar grade Copper sulphate (0.03M), Indium sulphate (0.05 M) and 0.005 M Selenium oxide was used for the deposition of films. The deposition current density was 1.0 mA cm-2. The films were deposited at different electrolyte temperatures in the range of 30 - 80°C. Thickness of the films estimated by Mitutoyo surface profilometer increased from 400 nm to 800 nm.The typical XRD patterns of CIS films deposited at different electrolyte temperatures exhibit the chalcopyrite structure which is easily identified for the films (JCPDS card no. 00-040-1487). The films deposited at lower electrolyte temperatures, show a poor crystallinity with weak and broadened diffraction peaks. As the electrolyte temperature increases, the diffraction peaks become sharp and the peak intensity also increases. Three well defined characteristic peaks at 26.6°, 44.1° and 52.4°are observed. The crystallite size of the films calculated using Scherrer’s equation varied from 15 – 40 nm with duty cycle. Dislocation density and strain were calculated.Composition of the films determined from EDAX measurement indicated that as the electrolyte temperature increased the films became more stoichiometric. At lower electrolyte temperature slight excess of copper is deposited compared to indium since, the deposition potential for copper is more positive compared to indium and a lower concentration of indium ions are available for deposition. At higher electrolyte temperatures, the concentration of the indium ion increases, hence the Cu/In ratio approaches unity at 80°C.The band gap of the films increased from 1.05 eV to 1.17 eV as the electrolyte temperature decreased. The increase in band gap at lower temperatures is due to the small crystallites. The values of the band gap agree well with the earlier report.The room temperature transport parameters were measured by Hall Van der Pauw technique by providing gold ohmic contact. The magnitude of the resistivity increased from 0.1 ohm cm to 20.0 ohm cm as the electrolyte temperature is increased. The resistivity values are comparable to earlier report on three source evaporated films.Solar cell structure of the configuration, Mo/CuInSe2/CuInS2/Ag was studied. For solar cell studies, CuInSe2 films were brush electrodeposited at different bath temperatures on Molybdenum substrate, over this layer, n-CuInS2 films ( 400 nm) were brush electrodeposited at 80°C. The resistivity of the CuInS2 layer was 2.0 ohm cm. On top of the CuInS2, a silver grid was vacuum evaporated. The solar cell parameters, open circuit voltage (Voc), short circuit current density (Jsc), series resistance (Rs),shunt resistance (Rsh), and fill factor (FF) were studied under 100 mW cm-2. The cell area was 0.65 cm2. The results show that the cells exhibit higher efficiency compared to an earlier report on pulse reverse deposited CuInSe2 films.The results of this work clearly point to the possibility of successfully employing the brush electrodeposition technique for the growth of CIS films with grain size in the range of 15 – 40 nm and for the preparation of films with resistivity in the range of 0.1 – 20.0 ohm cm.

Solar-driven hydrogen evolution using a CuInS2/CdS/ZnO heterostructure nanowire array as an efficient photoanode.

Photoanodes prepared using CuInS2/CdS/ZnO nanowires were fabricated by a solution-based process for constructing a photo-driven hydrogen generation system. For efficient light harvesting and photoexcited charge collection, ZnO nanowire (NW) photoanode arrays were co-sensitized with CdS and CuInS2 (CIS). A CdS layer was deposited on the ZnO NW via successive ion layer adsorption and reaction (SILAR), and the CIS layer was prepared by depositing a molecular precursor solution onto the CdS/ZnO NW. The generated anodic photocurrent was increased with the subsequent deposition of the CIS and CdS layers. Ultraviolet photoelectron spectroscopy analysis revealed cascade type-II band alignments for the CIS/CdS/ZnO NW photoanodes, which enabled efficient electron collection. Our heterostructure photoelectrode has generated a greatly improved photocurrent density of 13.8 mA cm(-2) at 0.3 V vs. SCE under 1 sun illumination.

Effect of Annealing on the Photoelectrochemical Behavior of CuInS2 Nanocrystal Films

Photovoltaics based on inorganic thin film absorber layers such as CuInS2 (CIS) are showing promise in overcoming the increasing energy demand. There are, however, challenges that CIS presents before it can be considered cost effective. A typical synthesis employs a high temperature (∼500°C) annealing step with a H2S atmosphere, which can significantly raise the cost of the photovoltaic devices. In this work we report a relatively low temperature, H2S free annealing step (250°C) that produced a photocurrent enhancement in the CIS nanocrystal film based on the comparison of respective photoelectrochemical measurements. Investigations into the effects of annealing on the morphology, composition, crystallinity and temperature of degradation of the film were carried out. A thin CdS buffer layer can provide photocurrent enhancement of the CIS layer, but it is typically added after annealing because temperatures above 300°C will degrade optical properties. The low annealing temperature allowed for CIS and the CdS buffer layer to be annealed together, which produced a further photocurrent density enhancement. The combination of a low temperature annealing along with a large photocurrent enhancement of the CIS/CdS bi-layer could help to improve efficiency in the full device fabrication while still keeping costs low.

In situ growth of CuInS2 nanocrystals on nanoporous TiO2 film for constructing inorganic/organic heterojunction solar cells

Inorganic/organic heterojunction solar cells (HSCs) have attracted increasing attention as a cost-effective alternative to conventional solar cells. This work presents an HSC by in situ growth of CuInS2(CIS) layer as the photoabsorption material on nanoporous TiO2 film with the use of poly(3-hexylthiophene) (P3HT) as hole-transport material. The in situ growth of CIS nanocrystals has been realized by solvothermally treating nanoporous TiO2 film in ethanol solution containing InCl3 · 4H2O, CuSO4 · 5H2O, and thioacetamide with a constant concentration ratio of 1:1:2. InCl3 concentration plays a significant role in controlling the surface morphology of CIS layer. When InCl3 concentration is 0.1 M, there is a layer of CIS flower-shaped superstructures on TiO2 film, and CIS superstructures are in fact composed of ultrathin nanoplates as ‘petals’ with plenty of nanopores. In addition, the nanopores of TiO2 film are filled by CIS nanocrystals, as confirmed using scanning electron microscopy image and by energy dispersive spectroscopy line scan analysis. Subsequently, HSC with a structure of FTO/TiO2/CIS/P3HT/PEDOT:PSS/Au has been fabricated, and it yields a power conversion efficiency of 1.4%. Further improvement of the efficiency can be expected by the optimization of the morphology and thickness of CIS layer and the device structure.

Photovoltaic performance of bithiazole-bridged dyes-sensitized solar cells employing semiconducting quantum dot CuInS2 as barrier layer material

In this work, the quantum dot CuInS2 layer was deposited on TiO2 film using successive ionic layer absorption and reaction (SILAR) method, and then two bithiazole-bridged dyes (BTF and BTB) were sensitized on the CuInS2/TiO2 films to form dye/CuInS2/TiO2 photoanodes for DSSCs. It was found that the quantum dots CuInS2 as an energy barrier layer not only could effectively improve open-circuit voltage (Voc) of solar cell, but also increase short-circuit photocurrent (Jsc) compared to the large decrease in Jsc of ZnO as energy barrier layer. The electrochemical impedance spectroscopy (EIS) measurement showed that the CuInS2 formed a barrier layer to suppress the recombination from injection electron to the electrolyte and improve open-circuit voltage. Finally, the open-circuit voltage increased about 22 and 27mV for BTF and BTB-/CuInS2/TiO2-based cells, the overall conversion efficiencies also reached to 7.20% and 6.74%, respectively.

Studies in CuInS2 based solar cells, including ZnS and In2S3 buffer layers

The influence of the growth conditions on the surface chemistry and on the homogeneity of the chemical composition of CuInS2 (CIS) thin films, prepared by sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process, was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the growth temperature affects the phase in which this compound grows. The samples deposited at temperatures around 500°C (2nd stage) contain mainly the CuInS2 phase; however, secondary phases like In2S3, Cu2S were additionally identified at the surface and in the bulk of CuInS2 samples deposited at temperatures greater than 550°C. Also, the elemental composition of the layers constituting the Glass/Mo/CuInS2/buffer/ZnO structure was studied through Auger electron spectroscopy (AES) depth profile measurements. AES measurements carried out across the Glass/Mo/CuInS2/buffer/ZnO heterojunction gave evidence of Cu diffusion from the CuInS2 layer towards the rest of the layers constituting the device, and of the formation of a MoS2 layer in the Mo/CuInS2 interface. The performance of CuInS2-based solar cells fabricated using CBD (chemical bath deposition) deposited ZnS as buffer layer was compared to that of cells fabricated using CBD deposited In2S3 as buffer.

Bulk Heterojunction Formation between Indium Tin Oxide Nanorods and CuInS2 Nanoparticles for Inorganic Thin Film Solar Cell Applications

In this study, we developed a novel inorganic thin film solar cell configuration in which bulk heterojunction was formed between indium tin oxide (ITO) nanorods and CuInS(2) (CIS). Specifically, ITO nanorods were first synthesized by the radio frequency magnetron sputtering deposition method followed by deposition of a dense TiO(2) layer and CdS buffer layer using atomic layer deposition and chemical bath deposition method, respectively. The spatial region between the nanorods was then filled with CIS nanoparticle ink, which was presynthesized using the colloidal synthetic method. We observed that complete gap filling was achieved to form bulk heterojunction between the inorganic phases. As a proof-of-concept, solar cell devices were fabricated by depositing an Au electrode on top of the CIS layer, which exhibited the best photovoltaic response with a V(oc), J(sc), FF, and efficiency of 0.287 V, 9.63 mA/cm(2), 0.364, and 1.01%, respectively.