Thin Film Heterojunction Research Articles

Bias dependent NDR in TiO2/NiO heterojunction diodes

TiO2/NiO thin film heterojunction diodes are fabricated using electron beam evaporation and DC sputtering techniques. Three different thicknesses of NiO (58, 82, and 160 nm) are combined with a TiO2 film of about 80 nm thick. The common device configuration is FTO/TiO2/NiO/Au with a 4 mm sq. device area. The thickness dependent diode I-V characteristics were analyzed; with the increase in thickness, the diode knee voltage, series resistance, and ideality factor have reduced. All the devices exhibit a high diode ideality factor, which means the diode currents are not limited by drift, diffusion, or recombination at the space charge region. The high ideality factor points to the presence of interface states, spatial inhomogeneities, or tunneling in the devices. Further, the bias dependent negative differential resistance (NDR) in I-V characteristics and the presence of an anomalous peak in C-V characteristics were analyzed, which claimed the presence of interfacial trap states, defects, or tunneling in the diodes. The Fowler-Nordheim tunnel model was applied to the devices and the field enhancement factors were calculated as −14.3, −9.3, and −9.2 for the diodes in the increasing order of thickness. The tunneling phenomenon was confirmed as trap-assisted indirect tunneling. Also, the temperature dependence of NDR was studied.

Enhancement in microstructural and optical properties of thermally evaporated CdTe/CdSe heterojunction thin Films

The optimization of microstructural and optical properties of a thin layer is an important step prior device fabrication process, so an enhancement in these properties of thermally evaporated CdTe/CdSe thin films was reported in this work. We choose to research (CdSe) materials as a n-type absorber layer in the CdTe/CdSe heterojunction thin film. The Effect of annealing temperature on the structural and optical properties of CdTe/CdSe Heterojunction thin films was studied, using various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and Double-beam computer-controlled spectrophotometer in the wavelength between 200 nm and 2500 nm. Diffraction (XRD) patterns showed that the as-prepared films were amorphous nature, whereas the annealed films were polycrystalline. These results were confirmed by scanning electron microscopy investigations. It was found that the crystallite size and degree of crystallinity of the studied films depend on the annealing temperature. Furthermore the optical measurement shows that this treatment shifts the optical absorption edge at low energy and decreases the optical band gap from 1.92 eV, to 1.37eV while the values Urbach energy increase as the annealing temperature increased from 300 K to 433 K. As consequence is that the heat treatment improves the quality of the CdTe/CdSe heterojunction thin films for the potential use in photovoltaic applications.

Regulation of solar cell performance by cadmium sulfide/copper-based thin film heterojunction annealing under different atmospheres

Efficient copper based thin film solar cells usually use inorganic n-type semiconductor material CdS as the buffer layer. Therefore, the interface quality and energy band matching between the buffer layer and the absorption layer are crucial to the collection and utilization of carriers. Heat treatment can promote the mutual diffusion of interface elements, the migration of ions in the material, and the change of defect state, and the appropriate temperature will change the Cu-Zn ordering degree in the absorption layer, so as to improve the efficiency of the solar cells. Based on the optimization of CdS basic process, the strategy of annealing CdS/copper-based thin film heterojunction in sulfur atmosphere further improves the quality of CdS thin film, and is applied to copper-based solar cells to regulate the p-n heterojunction energy band gap matching of copper-based thin film cells. The results show that the annealing of CdS thin film in sulfur-containing inert atmosphere can effectively improve the crystal quality of CdS thin film and inhibit the non-radiative recombination loss caused by defect trapping at the interface of CZTS/CdS heterojunction, and the open-circuit voltage of the device can significantly increase to 718 mV. In addition, annealing CZTS/CdS heterojunction in S/Ar atmosphere can effectively improve the p-n heterojunction energy band gap matching, which not only improves the electron transmission, but also reduces the carrier recombination, thus improving the <i>V</i><sub>oc</sub> and FF of the device. Besides, the oxygen element in CdS film can be replaced by sulfur element in sulfur atmosphere to improve the quality of CdS film, and thus enhancing the short-wave absorption of solar cell device. Therefore, in terms of device efficiency, the efficiency of CZTS solar cell based on sputtering method increases from 3.47% to 5.68%, which is about twice that of non-annealing treatment. Its device structure is Glass/Mo/CZTS/CdS/i-ZnO/Al:ZnO/Ni/Al, providing a reliable process window for copper based thin film solar cell devices to achieve high open-circuit voltage. Meanwhile, this study strongly demonstrates the importance of annealing atmosphere selection for CdS quality and energy band matching of CZTS/CdS heterojunction. In addition to interface interdiffusion, the composition and crystallinity of thin film material are controlled.

Tailoring the optical and electrical behavior of Cu2O/ZnO heterojunction by varying the Zn2+ ion concentration for solar-cell applications

Heterojunctions made from metal oxide semiconductors are of great interest due to their harmless non-toxic property, enormous availability, and chemically stable nature. In this work, we report the fabrication of Cu2O/ZnO heterojunction by deposition of p-type Cu2O followed by n-type ZnO via an inexpensive spin coating method at ambient conditions. This report focuses on the study of the properties of Cu2O/ZnO heterojunction thin films with different precursor concentrations of ZnO (0.05 M, 0.1 M, 0.15 M, 0.2 M, and 0.25 M). The structural, morphological, optical, and electrical properties are performed for different compositions. The band gap of all Cu2O/ZnO heterojunction thin films ranges between 1.86 eV and 2.02 eV. The IV characteristics confirm p-n photoactive heterojunction behavior for all the samples with increased current density for lower Zn2+ ion concentration.

Characterization of TiO2 NPs/ZnO NSs heterojunction thin film on PTFE substrate growth by dip coating process

In this work, dip coating process (DCP) was used to synthesize TiO2 nanoparticles (NPs). The photocatalytic nanostructured heterojunction was formed on ZnO nanoseeds (NSs) layer grown by radio frequency (RF) sputtering on flexible Teflon (PTFE) substrate. Series of characterizations and analyses reveal the morphology, optical, and structural properties of the nanocomplexes. These include several identified peaks observed by XRD. While, UV-Vis reflectance spectroscopy, photoluminescence (PL), and FTIR were utilized to determine the opto-characteristics, and to observe the presence of functional bonds involved in the growth of the heterojunction thin film. Based on the presented results, the heterostructures relying on a flexible substrate are believed to be highly promising for photocatalytic applications.

Electrodeposition of Copper Oxides as Cost-Effective Heterojunction Photoelectrode Materials for Solar Water Splitting

Photoelectrocatalytic hydrogen production is crucial to reducing greenhouse gas emissions for carbon neutrality and meeting energy demands. Pivotal advances in photoelectrochemical (PEC) water splitting have been achieved by increasing solar light absorption. P-type Cu-based metal oxide materials have a wide range of energy band gaps and outstanding band edges for PEC water splitting. In this study, we first prepared Cu2O thin films using electrodeposition and fabricated a heterojunction structure of CuO/Cu2O by controlling annealing temperatures. The surface morphological, optical, and electrochemical properties were characterized using various analytical tools. X-ray and Raman spectroscopic approaches were used to verify the heterojunction of CuO/Cu2O, while surface analyses revealed surface roughness changes in thin films as the annealing temperatures increased. Electrochemical impedance spectroscopic measurements in conjunction with the Mott–Schottky analysis confirm that the CuO/Cu2O heterojunction thin film can boost photocurrent generation (1.03 mA/cm2 at 0 V vs. RHE) via enhanced light absorption, a higher carrier density, and a higher flat band potential than CuO and Cu2O thin films (0.92 and 0.08 mA/cm2, respectively).

Performance analysis of n-TiO2/p-Cu2O, n-TiO2/p-WS2/p-Cu2O, and n-TiO2/p-WS2 heterojunction solar cells through numerical modelling.

A new hetero-structure of n-TiO2/p-WS2/p-Cu2O is proposed as a potential candidate for solar energy generation using tungsten disulfide (WS2) as an absorber layer. The proposed device performance is simulated by employing a one-dimensional solar cell capacitance simulator (SCAPS-1D). The numerical simulation studies compared the performances of n-TiO2/p-Cu2O, n-TiO2/p-WS2/p-Cu2O, and n-TiO2/p-WS2 hetero-structures based on various physical parameters like interface defects density, bulk defects density, absorber layer thickness, series resistance, shunt resistance, and operating temperature. In our simulation investigations, we found that interface defects pose a formidable impact on heterojunction devices. Interface defects closer to the front surface severely deteriorate the performances than the back surface. The bandgap of the absorber layer influences the performances of the solar cells. A closer comparison between n-TiO2/p-Cu2O and n-TiO2/p-WS2 heterojunction solar cells (HJSCs) revealed that the latter (n-TiO2/p-WS2) has nearly 182% better performance than the former (n-TiO2/p-Cu2O) devices. Additionally, the performance of the n-TiO2/p-WS2 solar cell is further boosted by ~ 139% in the presence of a hole transport layer of p-Cu2O. The best-simulated efficiency of the proposed new hetero-structure (n-TiO2/p-WS2/p-Cu2O) solar cell is 28.86%. Moreover, these optimized physical parameters may shed light on "easy to apply" new path for fabrication of a non-toxic, environment-friendly, and highly efficient novel thin-film heterojunction (n-TiO2/p-WS2/p-Cu2O) solar cell.

Facile preparation and characterization of nanostructured ZnS/PbS heterojunction thin films for enhanced microbial inhibition and photocatalytic degradation

In the present study, we report for the first time the elaboration of n-ZnS/p-PbS heterojunction thin film by spin-coating method and its antimicrobial and photocatalytic activities. The resulting films were characterized using XRD, XPS, FESEM, and EDS. The FESEM results revealed uniform nanostructures films with small spherical shapes and slight variation in diameter. XRD and XPS analysis confirmed the growth of crystalline ZnS and PbS thin films. Photocatalytic degradation of organic dyes was investigated with the elaborated nanocomposite ZnS/PbS under sunlight. The degradation rates of 91.2, 87.1 68.6, and 34.4% were achieved for methylene blue, malachite green, red congo, and methyl orange, respectively. The utilization of heterojunction thin layers assembly enhances the photocatalytic degradation process. The antibacterial and antifungal activities of the coated ZnS/PbS films exhibited considerable behaviour against Staphylococcus aureus, Escherichia coli, and Candida albicans.The present work has not only offered a simple method for the degradation of organic pollutants, but it presents an answer to reduce the rate of microbial contamination.

Hybrid C8-BTBT/InGaAs nanowire heterojunction for artificial photosynaptic transistors

The emergence of light-tunable synaptic transistors provides opportunities to break through the von Neumann bottleneck and enable neuromorphic computing. Herein, a multifunctional synaptic transistor is constructed by using 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and indium gallium arsenide (InGaAs) nanowires (NWs) hybrid heterojunction thin film as the active layer. Under illumination, the Type-I C8-BTBT/InGaAs NWs heterojunction would make the dissociated photogenerated excitons more difficult to recombine. The persistent photoconductivity caused by charge trapping can then be used to mimic photosynaptic behaviors, including excitatory postsynaptic current, long/short-term memory and Pavlovian learning. Furthermore, a high classification accuracy of 89.72% can be achieved through the single-layer-perceptron hardware-based neural network built from C8-BTBT/InGaAs NWs synaptic transistors. Thus, this work could provide new insights into the fabrication of high-performance optoelectronic synaptic devices.

Effect of Al doped ZnO on optical and photovoltaic properties of the p-Cu2O/n-AZO solar cells

Metal oxide thin films have fared so well in the semiconductor industry because of their superior physical, electrical, and optical properties. The applications of these materials in solar cells, biosensors, biomedicine, supercapacitors, photocatalysis, luminous materials, and laser systems are becoming increasingly popular. In this study, the influence of Al concentration on Cu2O/AZO heterojunction thin films was examined systematically. First, arrays of n-ZnO and AZO rods were produced on an ITO substrate using a hydrothermal technique at 140 °C. Then, using an alkaline cupric lactate solution, a thin films of p-Cu2O were electrodeposited at 60 °C onto the ZnO arrays. The structure and morphology of the produced materials and the solar cells were studied using X-ray diffraction and scanning electron microscopy. The optical measurements demonstrate a shift in the absorption edge with increasing Al content. Solar cells have been created with a device structure of ITO/ZnO/Cu2O/Al and ITO/Al-doped ZnO/Cu2O/Al configurations. The power conversion efficiency (ɳ) of the inorganic solar cell with 6% Al-doped ZnO is ɳ = 0.282%, which is greater than the ɳ of the ZnO-based solar cell (ɳ = 0.17%).

Built-in Electric Field for Efficient Charge Separation and Ionic Transport in LiCoO2/SnO2 Semiconductor Junction Fuel Cells

Built-in electric field (BIEF)-induced charge transfer in planar and bulk junctions has significantly improved electrochemical performance in current and advanced energy storage devices such as lithium, sodium, and aluminum batteries. In this study, fuel cells with different junctions based on semiconductor membranes were designed in thin-film planar, bulk planar, and bulk heterojunction (BHJ) configurations to investigate the BIEF effects on their electrochemical performance. These semiconductor membrane fuel cells were constructed with p-type LiCoO2 and n-type SnO2 sandwiched between Ni0.8Co0.15Al0.05LiO2 (NCAL) electrode semiconductors. At 600 °C, the fuel cells with bulk heterojunction (BHJ), bulk planar p–n junction, and thin-film planar p–n junction deliver remarkable peak power densities of 0.82, 0.61, and 0.28 W/cm2 in H2/air operation, respectively. The band structures were determined and the charge transport properties and device operation were investigated. Our results show that the semiconductor membrane-based devices are a good alternative to replace the conventional electrolyte membrane fuel cells for the next generation of fuel-to-electricity conversion technology.

Performance evaluation of transparent self-powered n-ZnO/p-NiO heterojunction ultraviolet photosensors

We have constructed NiO/ZnO thin film heterojunction diodes by dc magnetron sputtering technique and evaluated their performance for ultraviolet sensor applications. The constructed device configuration, ITO/ZnO/NiO/Ag exhibited excellent current-voltage rectifying characteristics in the order of 10 5 at room temperature. The effect of rapid thermal annealing treatment on the fabricated ITO/ZnO/NiO thin film stack was evaluated for their photodetector characteristics. The structural, optical, and spectroscopic properties were also investigated. Further, the ITO/ZnO/NiO/Ag diodes were tested under 365 nm UV light illumination having a power density of 0.06 mW/cm 2 . Remarkably, a speed of response with rise/fall time of 197.29/537.10 ms has been recorded at self-powered mode. Interestingly, the photodiode device has exhibited a spectral responsivity of 13.01 mA/W and stable photo detectivity of 5.66 × 10 11 Jones at room temperature. The n-ZnO/p-NiO heterojunction photodetector has shown its ability to detect a faint UV light in a self-powered mode. • Fabricated transparent p-NiO/n-ZnO heterojunction by dc magnetron sputtering with an excellent photo-to-dark current ratio. • It operated in a self-powered mode under 365 nm wavelength of a low optical power source i.e., 0.06 mW/cm 2 . • Achieved excellent speed of response of rising and fall time of 197.29 ms and 537.10 ms respectively. • At Zero bias, responsivity varied from 13.01 mA/W to 6.52 mA/W and EQE 4.42 % to 2.21 % as a function of rapid thermal annealing.

Ag-decorated CuO NW@TiO2 heterojunction thin film for improved visible light photocatalysis

Herein, Ag-decorated CuO@TiO2 (CuO@TiO2-Ag) semiconductor heterojunctions are prepared using a porous CuO nanowire (NW) matrix for visible light photocatalysis applications. The CuO NW matrix is synthesized by wet-oxidation-based growth on a commercial Cu plate. Conformal coating of TiO2 on the CuO NW surfaces is successively achieved by atomic layer deposition, following which Ag nanoparticles (NPs) are deposited to synthesize a Ag-decorated CuO@TiO2 photocatalyst film. Microstructural and chemical analyses reveal uniform synthesis of a CuO@TiO2 heterojunction as well as a binding energy shift at the interface to form balanced Fermi energy, respectively. The performance of CuO@TiO2-Ag as a visible-light photocatalyst is evaluated under 20-W low-power visible-light LED illumination for the photodegradation of methylene blue. In addition, the effects of the TiO2 layer and the Ag NPs on the decomposition efficiency are investigated. To control the thickness of TiO2 and the dosage of Ag NPs, the photodegradation of CuO@TiO2-Ag is optimized at a rate of 0.0133 min−1, which is approximately 3 and 2.5 times higher than those of a bare CuO@TiO2 heterojunction and Ag-deposited CuO, respectively. The high decomposition efficiency achieved in this study results from the combined effects of the conformal core–shell heterojunction formed by atomic layer deposition and the well-distributed Ag NPs.

Deposition of Cu2ZnSnS4 thin film at different solution flow rates

A thin film of Cu2ZnSnS4, a potential compound semiconductor for the absorber layer in thin film heterojunction solar cells, has been successfully deposited using the spray pyrolysis process. The influence of solution spray rate on deposited film characteristics is investigated. The structural and optical properties of the films have been studied. X-ray diffraction studies revealed the films are polycrystalline in nature with the kesterite structure and the lattice parameters are found to be a = b = 0.542 nm and c = 1.082 nm. Micro Raman spectra confirm the Cu2ZnSnS4 crystal phase. Optical band gap, evaluated from spectral transmittance data, which is close to 1.5 eV. The absorption coefficient of these films is ≥ 104 cm−1. These films are found to be p-type in nature. Finally, work on fabricating a conventional thin film heterojunction solar cell has been undertaken.

Improved n-ZnO nanorods/p-Si heterojunction solar cells with graphene incorporation

The present research explored the effect of graphene layer and zinc oxide nanorods (NRs) on the photovoltaic performance of ZnO thin film-based heterojunction solar cells. For this purpose, ZnO thin film was deposited on p-type silicon using radio frequency sputtering to serve as an anti-reflective layer and n-type semiconductor to form a heterojunction thin film solar cell. Then, a cost-effective and facile chemical bath deposition technique was employed to synthesize ZnO NRs. To study the effect of reduced graphene oxide (rGO) on the optical properties of ZnO NRs, the colloidal suspension of rGO and ZnO NRs (rGO:ZnO NRs) was prepared. The optimized nanostructures were then transferred to the surface of the ZnO/Si sample using a drop-cast method. The morphological examination of the nanostructures showed the formation of ZnO NRs with various orientations which can significantly increase the entrapment of incident photons. The XRD results indicated an improvement in the structural properties of ZnO NRs upon adding rGO flakes. The reduction of GO was confirmed using Raman spectroscopy. The higher ID/IG ratio for the rGO:ZnO NRs sample (compared to GO layers) suggested the chemical reduction of GO. The optical investigations revealed an increment in the light absorption and PL intensity in the rGO-containing samples which can be due to the role of graphene as a reinforcement phase to inhibit the electron-hole recombination. The optoelectrical properties of fabricated solar cells were investigated via the metallization of top and rear contacts to fabricate three different solar cells based on ZnO thin film, ZnO NRs, and rGO:ZnO NRs. The results showed an enhancement in the efficiency (14.12%) and the fill factor (0.552) of the solar cell based on rGO:ZnO NRs compared to the other solar cells. Therefore, the incorporation of rGO can improve the photovoltaic properties of solar cells based on ZnO nanorods.

All-organic flexible heterojunction thin film photodetectors based on phthalocyanines/C60

In modern organic photoelectric detection, a broad spectrum response is much needed. Unfortunately, it remains a huge challenge in the field of optoelectronics. In this work, a photodetector based on phthalocyanines/C60 thin film heterojunction was fabricated by in situ secondary evaporation. Most encouragingly, the device has no selectivity to the substrate and can grow well on the flexible substrate, and the performance of the device changes merely 7.27% after 104 bending cycles, which shows its stability performance. The device has the ability to detect a wide band from visible light to near infrared. The largest Ri of the device was obtained reaching up to 0.94 A W−1, with crest value D* equals to 4.7 × 1012 Jones. The all-organic heterojunction devices prepared by us have the advantages of simple preparation method, low cost, and no selectivity to the substrate, which shows a very good application potential in the fields of flexible wearable and infrared remote sensing imaging in the future.

Growth of nano-branches on 1-D WO3 nanotrees by flame process and its photoelectrochemical performances

Flame vapor deposition (FVD) is a powerful method to prepare rapidly and economically the nanostructured thin film with high purity and high crystallinity. One-dimensional (1-D) nanostructured tungsten oxide (WO 3 ) thin film has high potential for various applications as photocatalytic material and, in this study, was prepared from tungsten wire as a precursor by FVD process. The nucleation and growth rates in FVD process could be controlled by changing the precursor supply rate in flame instantaneously by installing additional wire traverse feeder and the nanotree structured WO 3 thin film was prepared successfully. The concentration of nano-branches at nanotree structured WO 3 thin films could be controlled by adjusting wire traversing speed. The proper wire traverse feeding speed could increase surface area and allow more light absorption by additional growth of nano-branches, but too low wire traverse feeding speed could make random and dense growth of nano-branches to reduce the electrical properties and total surface area. The proper growth of nano-branches could increase the photoelectrochemical (PEC) performance of WO 3 /BiVO 4 heterojunction thin film by providing the larger interfacial contact area for heterojunction, but too much growth of nano-branches could reduce the PEC performance because of non-uniform loading of BiVO 4 in WO 3 thin film during spin-coating process. This study can be a basis to prepare by FVD process not only the nanotree structured WO 3 thin film for its PEC application but also many nanostructured thin films of various materials for their suitable applications. • Nanotree structured WO 3 thin film was successfully prepared by 1-step flame process. • The precursor concentration could be changed sharply by the wire traversing feeder. • Nucleation and growth rates were controlled to prepare nano-branches on nanotrees. • Nanotree structured WO 3 /BiVO 4 film improved photoelectrochemical performance. • Proper growth of nano-branch is important for high photoelectrochemical performance.

Back-End-of-Line Compatible InSnO/ZnO Heterojunction Thin-Film Transistors With High Mobility and Excellent Stability

We examine low-temperature fabricated InSnO/ZnO (ITO/ZnO) heterojunction thin-film transistors (TFTs) with high mobility and excellent stability. The effects of ITO thickness (0, 2, 4, 6, and 8 nm) on performance of the ITO/ZnO TFTs are studied. For the devices with a 6-nm ITO layer, a field-effect mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{\mathrm{FE}}$ </tex-math></inline-formula> ) of 55.50 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, a subthreshold swing (SS) of 113.22 mV/decade, a turn-on voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\mathrm{ON}}$ </tex-math></inline-formula> ) of −3 V, and an on/off current ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{\mathrm{ON}}/\text{I}_{\mathrm{OFF}}$ </tex-math></inline-formula> ) over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> are obtained. Besides, the devices demonstrate excellent stability with a threshold voltage shift of 0.68 and −0.25 V under the positive and negative gate-bias stress, respectively. Operation mode of the ITO/ZnO TFTs is analyzed. The results show that potential well at ITO/ZnO heterointerface forms electronic accumulation, which is beneficial to improve the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{\mathrm{FE}}$ </tex-math></inline-formula> of the ITO/ZnO TFTs. Our work promotes applications of the oxide TFTs to back-end-of-line (BEOL) circuits.

Internal electric field-mediated sulfur vacancies-modified-In2S3/TiO2 thin-film heterojunctions as a photocatalyst for peroxymonosulfate activation: Density functional theory calculations, levofloxacin hydrochloride degradation pathways and toxicity of intermediates

Photocatalytic activation of peroxymonosulfate is considered an effective method for degrading organic pollutants. However, the difficulty in recovering powder photocatalysts restricts their practical applications. In this study, we hydrothermally generated sulfur-vacancy-modified In2S3/TiO2 thin films on fluorine-doped tin oxide substrates. We further investigated the formation mechanism of heterojunctions and the degradation pathways of levofloxacin hydrochloride by activated PMS using density functional theory calculations. Results from a series of experiments showed that the levofloxacin hydrochloride degradation performance by thin-film catalyst-activated peroxymonosulfate is comparable to that of powder photocatalysts, while the ease of recycling makes the thin film more suitable for applications in a real environment. Furthermore, the construction of heterojunctions and introduction of sulfur vacancies compensated for the poor separation efficiency of photogenerated electron-hole pairs in single photocatalysts. Overall, this study provides novel insights into the degradation of organic pollutants using thin-film photocatalysts in advanced oxidation processes.

Tailored Band Structure of Cu(In,Ga)Se2 Thin-Film Heterojunction Solar Cells: Depth Profiling of Defects and the Work Function.

An efficient carrier transport is essential for enhancing the performance of thin-film solar cells, in particular Cu(In,Ga)Se2 (CIGS) solar cells, because of their great sensitivities to not only the interface but also the film bulk. Conventional methods to investigate the outcoming carriers and their transport properties measure the current and voltage either under illumination or dark conditions. However, the evaluation of current and voltage changes along the cross-section of the devices presents several limitations. To mitigate this shortcoming, we prepared gently etched devices and analyzed their properties using micro-Raman scattering spectroscopy, Kelvin probe force microscopy, and photoluminescence measurements. The atomic distributions and microstructures of the devices were investigated, and the defect densities in the device bulk were determined via admittance spectroscopy. The effects of Ga grading on the charge transport at the CIGS-CdS interface were categorized into various types of band offsets, which were directly confirmed by our experiments. The results indicated that reducing open-circuit voltage loss is crucial for obtaining a higher power conversion efficiency. Although the large Ga grading in the CIGS absorber induced higher defect levels, it effectuated a smaller open-circuit voltage loss because of carrier transport enhancement at the absorber-buffer interface, resulting from the optimized conduction band offsets.