KCN Treatment Research Articles

Rel-dependent decrease in the expression of ribosomal protein genes by inhibition of the respiratory electron transport chain in Mycobacterium smegmatis.

In this study, we demonstrated that both the expression of most ribosomal protein genes and the amount of ribosomes were decreased in the Δaa 3 mutant of Mycobacterium smegmatis, in which the major terminal oxidase (aa 3 cytochrome c oxidase) of the respiratory electron transport chain (ETC) is inactivated, compared to those in the wild-type strain. Deletion of the rel gene encoding the major (p)ppGpp synthetase in the background of the Δaa 3 mutant restored the reduced expression of ribosomal protein genes, suggesting that inhibition of the respiratory ETC leads to the Rel-dependent stringent response (SR) in this bacterium. Both a decrease in the expression of ribosomal protein genes by overexpression of rel and the increased expression of rel in the Δaa 3 mutant relative to the wild-type strain support the Rel-dependent induction of SR in the Δaa 3 mutant. We also demonstrated that the expression of ribosomal protein genes was decreased in M. smegmatis exposed to respiration-inhibitory conditions, such as KCN and bedaquiline treatment, null mutation of the cytochrome bcc 1 complex, and hypoxia. The MprBA-SigE-SigB regulatory pathway was implicated in both the increased expression of rel and the decreased expression of ribosomal protein genes in the Δaa 3 mutant of M. smegmatis.

Spatial-temporal variations of proline and related amino acids reveal distinct nitrogenous utilization strategies in rice during detoxification of exogenous cyanide

Cyanide (CN−) pollution in agricultural systems impairs amino acid metabolism in rice plants, hence decreasing their quality and yield. Meanwhile, little is known about the effects of CN− assimilation on the innate pool of proline (Pro) and its synthesis-related amino acids (Pro-AAs) in rice plants. In this study, a hydroponic experiment was carried out to investigate the effect of exogenous KCN on indigenous levels of Pro-AAs, i.e., Pro, glutamate (Glu), arginine (Arg), and ornithine (Orn) in rice seedlings fertilized with either nitrate (NO3−) or ammonium (NH4+) through the biochemical and RT-qPCR analysis. At the same KCN treatment concentration, the relative growth rate of NH4+-fed rice seedlings was considerably higher than that of NO3−-fed rice seedlings, but the residual concentration of CN− in NH4+-fed rice tissues was lower than that of NO3−-fed rice tissues. Based on the UPLC and stoichiometry molar ratio calculations, it is evident that the Glu pathway contributed significantly to Pro synthesis in rice under KCN + NO3− treatments; whereas the Orn pathway governed the synthesis of Pro in rice under KCN + NH4+ treatments. Moreover, transcriptional and bioinformatics analysis revealed that NH4+ fertilization resulted in spatial-temporal differences in the genetic response in rice tissue during detoxification of CN− compared with KCN + NO3− treatments. These findings suggested that the innate level of Pro serves as “a fishing float” to balance the flux between Pro and Pro-AAs in exogenous KCN-treated rice plants under different nitrogenous nutritional conditions.

Over 11% Efficient CuGaSe2 Solar Cells Without Using KCN Treatment

CuGaSe2 (CGS) has a bandgap energy of 1.68 eV and is theoretically very suitable to be in tandem with silicon or Cu(In,Ga)Se2 solar cells. However, due to the high quantity of surface defects, high‐performance CGS usually relies on a KCN surface treatment, which is a high‐toxic process and restricts its further development. Herein, by reducing the exposure time to air of the CGS layer as far as possible and developing a new absorber growth procedure to reduce the surface Cu x Se generation, grain size is successfully increased and interface recombination is reduced without the use of KCN. Combined with a simple annealing process, the defect concentration is successfully decreased and the depletion width is broadened dramatically and the power conversion efficiency is promoted to 11.05% without any traditionally used KCN treatment. This work provides a nontoxic and low‐pollution way to fabricate high‐efficient CGS solar cells.

High-Intensity Red Light-Emitting Diode Irradiation Suppresses the Inflammatory Response of Human Periodontal Ligament Stem Cells by Promoting Intracellular ATP Synthesis.

Periodontitis is an inflammatory lesion in the periodontal tissue. The behavior of human periodontal ligament stem cells (hPDLSCs), which play an important role in periodontal tissue regeneration, is restricted by the influence of inflammatory mediators. Photobiomodulation therapy exerts anti-inflammatory effects. The purpose of this study was to investigate the effects of light-emitting diode (LED) irradiation on the inflammatory responses of hPDLSCs. The light source was a red LED (peak wavelength: 650 nm), and the total absolute irradiance was 400 mW/cm2. The inflammatory response in hPDLSCs is induced by tumor necrosis factor (TNF)-α. Adenosine triphosphate (ATP) levels and pro-inflammatory cytokine (interleukin [IL]-6 and IL-8) production were measured 24 h after LED irradiation, and the effects of potassium cyanide (KCN) were investigated. LED irradiation at 6 J/cm2 significantly increased the ATP levels and reduced TNF-α-induced IL-6 and IL-8 production. Furthermore, the inhibitory effect of LED irradiation on the production of pro-inflammatory cytokines was inhibited by KCN treatment. The results of this study showed that high-intensity red LED irradiation suppressed the TNF-α-stimulated pro-inflammatory cytokine production in hPDLSCs by promoting ATP synthesis. These results suggest that high-intensity red LED is a useful tool for periodontal tissue regeneration in chronically inflamed tissues.

Chemical etching of tetrahedrite Cu10Cd2Sb4S13 monograin powder materials for solar cell applications

Cu10Cd2Sb4S13 micro-crystals were synthesized by molten salt method (so-called monograin powder growth) where the synthesis and growth of formed crystals proceeded in the isothermal solid-liquid equilibrium conditions in molten cadmium iodide at 480 °C. During cooling down process the oversaturated part of material dissolved in molten flux at synthesis-growth temperature starts to precipitate onto surfaces of the formed crystals changing the crystals' surfaces unevenly different from the crystals' bulk. To remove selectively the formed precipitates from crystals' surfaces, the tetrahedrite Cu10Cd2Sb4S13 powder crystals were chemically etched with different etchants: Br in methanol (Br2–MeOH), HCl (concentrated and diluted) and KCN. X-ray diffraction, Raman, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) characterization methods were used in this study. Morphology studies by SEM showed that treatment with diluted HCl and KCN etching, both resulted in smooth crystals’ surfaces. Surface analyses by Raman and XPS after etching with diluted HCl and KCN showed that the surface characteristics were almost identical to the features of the bulk of Cu10Cd2Sb4S13 crystals. As detected by SEM, XPS and Raman analyses, the Br2–MeOH solution reacted aggressively with micro-crystals forming elemental sulfur and oxides on the rough surfaces of crystals. Following KCN and/or HCl treatments removed these formed reaction products. XPS analysis confirmed that the oxidation states of the constituents of the synthesized tetrahedrite compound are as follows: Cu1+10Cd2+2Sb3+4S2-13. Using lasers with wavelength 532 and 633 nm, it was determined for the first time that Raman peaks in the range of 129–132 cm-1 and 167-173 cm-1 belong also to the Cu10Cd2Sb4S13 compound.

On KCN treatment effects on optical properties of Si-based bilayers

Abstract In this paper we report results from optical transmittance spectroscopy complemented with data from Raman scattering measurements to determine optical properties of two series of silicon based bilayers deposited by PECVD on glass substrate (intrinsic a-Si:H/p-type a-SiC:H and n-type mc-Si:H/intrinsic a-Si:H). These samples represent segments of common p-i-n thin film amorphous silicon solar cells with intrinsic hydrogenated silicon (a-Si:H) as the solar absorber. The members of the series differ by the KCN treatment conditions. Dispersive and absorptive optical properties – refractive indices, absorption coefficients and optical band gaps were determined from transmittance spectra. Each bilayer was considered as one effective thin film the optical properties of which can be regarded as effective optical properties of the bilayer structure. After KCN treatments refractive indices were modified probably due to the structural changes of bilayers. Moreover the effect of the solvent used in KCN solutions was recognized. Optical band gaps calculated either by the Tauc procedure or determined as iso-absorption levels were found to be only slightly KCN treatment dependent.

Free Radical Imaging for Visualization of Radiation Treatment Using Dynamic Nuclear Polarization (DNP) MRI

In vivo dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) enables the anatomical distribution of free radical species to be monitored. DNP enhances the MRI signal from nuclei such as 1H by irradiating tissue at the electron paramagnetic resonance (EPR) frequency of the free radical, before applying the MRI pulse sequence, thus increasing the image intensity where free radicals are present. Low-molecular-weight, stable nitroxyl compounds, including Tempol and carbamoyl-PROXYL (CmP), are organic free radicals that show antioxidant capability, and they have been used as redox sensitive contrast agent. The reduction of the nitroxyl compounds depend on production of free radicals which may be influenced by factors such as overproduction of reactive oxygen species (ROS) after radiation treatment. In this study, we evaluated the feasibility of visualization of free radical generation in solution and redox alteration of mice liver induced by radiation treatment, assessed by DNP-MRI with Tempol and CmP as a molecular imaging probe. Free radical imaging for monitoring of redox reaction was performed with a low magnetic field using an in vivo DNP-MRI system (Keller, Japan Redox Inc.). DNP-MRI image of phantom including Tempol or CmP and glutathion (GSH) as reductants was obtained before and after radiation treatment (0, 5, 10, 20 Gy). Quantification of Tempol and CmP radical was performed by electron paramagnetic resonance (EPR) spectroscopy. Pharmacokinetic DNP-MRI images of liver homogenate or mitochondrial solution with or without radiation (10 or 20 Gy) were obtained at 3, 5, 10, 15, 20, 25, 30, 35 and 40 min after addition of redox probes (1mM Tempol or CmP). The redox map was obtained by the slope of the enhanced DNP image intensity of each pixel from four pharmacokinetic images using a custom Excel macro program. Direct redox reaction between 0.3mM Tempol and 10 mM GSH was observed by EPR experiments. Therefore, we determined that 1mM GSH is suitable concentration for monitoring the redox reaction by radiation treatment. DNP-MRI clearly visualized the reduction of Tempol free radical. The DNP images clearly showed the significant enhancement in tissue homogenate and mitochondrial solution. The enhancement of DNP image was gradually reduced by liver homogenate solution due to reduction of Tempol and the reduction rate of Tempol was increased by the treatment of radiation. Interestingly, reduction of Tempol in both homogenates with or without radiation were completely inhibited by KCN treatment. It is suggested that enhancement of Tempol reduction is related in mitochondrial electron transfer system. We demonstrated that the visualization of ROS production by radiation treatment and mitochondrial redox metabolic change in the electron transfer chain using DNP-MRI.

In situ investigation of as grown Cu(In,Ga)Se2 thin films by means of photoemission spectroscopy

A UHV-transferred Cu(In,Ga)Se2 (CIGSe) thin film prepared by a three-stage process on an Mo-coated float glass was successfully investigated by detailed UPS/XPS and directly compared with air-transferred and cyanide etched samples from the same batch. Besides the fact that the valence band maximum of the UHV-transferred sample is located 1.19 eV below the Fermi level, pointing to a widened bandgap and type inversion, almost no oxygen or sodium was detected on the surface. After air transfer, Na- and O-containing species were found on the CIGSe surface that could be only partially removed upon cyanide etching. The residual and very low Na1s signal is slightly shifted, which is attributed to a modified band bending at the grain boundaries with Ga-, In-, and Se-related oxides still present on the CIGSe surface after the etching process. Thickness analysis reveals that both the sodium containing surface layer (after air-transfer) and the oxygen containing termination layer (after cyanide etching) are restricted to a few monolayers only. Finally, the topmost CIGSe layer appears to be Cu-free due to the fact that no oxidized Cu was found after air exposure. In addition, the Cu core level does not follow the surface termination induced shift of the valence band after the KCN treatment, pinning its maximum 0.77 eV below the Fermi level. These findings are ascribed to a Cu(In,Ga)7Se11 surface as deduced from XPS core level analysis.

Studies on the influence of etching solution on the properties of Cu2ZnSn(S,Se4) thin film solar cells

Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells (TFSCs) have emerged as the most promising low-cost alternatives to well-established CuInGaS2 and CuInS2-based TFSCs technologies. The surface composition of the absorber layer and the interface quality between the absorber and buffer layers play a key role in the performance of CZTSSe TFSCs. In this study, we investigated the influence of different etchants namely potassium cyanide (KCN), hydrochloric acid (HCl) and ammonia on different properties such as structural, morphological, and compositional as well as the solar cell performance of CZTSSe TFSCs. The results revealed no significant changes in the film structural properties before and after etching with any of the tested etchants. However, the slight changes in the composition and microstructure were observed after etching treatment. The microstructure was improved after KCN treatment with larger grain size compared to absorber layer without etching, whereas the slightly distorted microstructure with several surface pinholes was observed after HCl and ammonia treatment. Surprisingly, HCl and ammonia treatments degraded the open circuit voltage and fill factor values and thereby decreasing the power conversion efficiency (PCE) of the CZTSSe TFSCs. On the other hand, KCN treatment slightly improved the PCE of CZTSSe TFSCs. The decreased PCE after HCl and ammonia treatments could be mainly attributed to the deteriorated absorber quality as well as poor formation of poor juction between the absorber layer and the CdS buffer layer.

Imaging of Mitochondria Metabolic Change after Radiation Treatment using Dynamic Nuclear Polarization (DNP)-MRI

In vivo dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) enables the anatomical distribution of free radical species to be monitored. DNP enhances the MRI signal from nuclei such as 1H by irradiating tissue at the electron paramagnetic resonance (EPR) frequency of the free radical, before applying the MRI pulse sequence, thus increasing the image intensity where free radicals are present. Low-molecular-weight, stable nitroxyl compounds, including carbamoyl-PROXYL (CmP), are organic free radicals that possess SOD-like activity, and they have been used as probes in a variety of biophysical and biochemical experiments. The reduction rate of the radical probe depends on the tissue redox environment, which is influenced by factors such as overproduction of ROS and decreased antioxidant defences. In this study, we evaluated the feasibility of mitochondrial redox metabolic imaging, assessed by DNP-MRI with CmP as a molecular imaging probe, for detecting the metabolic change after radiation treatment to the tissue homogenate solution. Redox imaging of mitochondrial metabolism was performed with a low magnetic field using an in vivo DNP-MRI system (Keller, Japan Redox Inc.). The external magnetic field (B0) for EPR irradiation and MRI was fixed at 15 mT, and the radiofrequencies for EPR irradiation and MRI were 455 MHz and 683 kHz, respectively. DNP-MRI images of liver homogenate solution with or without radiation (10 or 20 gray) were obtained at 3, 5, 10, 15, 20, 25, 30, 35 and 40 min after starting measurement. The redox map was obtained by the slope of the enhanced DNP image intensity of each pixel from four pharmacokinetic images using a custom Excel macro program. Phantom redox experiments were conducted to examine the ability of CmP to participate in the mitochondrial redox reaction, and time-dependent changes in image contrast were assessed using liver tissue homogenate and KCN, an inhibitor of mitochondrial electron transfer chain. The DNP images clearly showed the significant enhancement in tissue homogenate solution by CmP. The enhancement of DNP-image was gradually reduced by liver homogenate solution due to reduction of CmP and the reduction rate of CmP was increased by the treatment of radiation. Interestingly, reduction of CmP in both homogenates with or without radiation were completely inhibited by KCN treatment. It is suggested that enhancement of CmP reduction is related in mitochondrial electron transfer system. We demonstrated that the mitochondrial redox metabolic change in the electron transfer chain after radiotherapy could be monitored by DNP-MRI with CmP as a redox probe.

Mitochondrial Complex IV Inhibition and Exogenous Oxidants Potently Synergize in Melanoma Cell Death Induction

Due to its functional duality in toxicity as well as signaling, research on therapeutic manipulation of reactive oxygen species (ROS) in cancer has been futile. Targeting melanoma cell death with excess amounts ROS, however, is difficult as these cells are highly resistant towards oxidative stress, creating a need for alternative and combinational approaches. Tumor metabolism mainly relies on aerobic glycolysis. We investigated a potential synergism of mitochondrial complex IV inhibition and exogenous-derived oxidants with both single treatment modalities being essentially non-toxic in melanoma cells. In this study, we investigated murine (metastatic B16F10 and non-metastatic B16F0) as well as human (SK-Mel 28) melanoma cells, and compared them with murine (primary fibroblasts) and human (HaCaT keratinocytes) non-cancer cells. Mitochondrial complex IV inhibition was realized using sodium azide (NaN3) and potassium cyanide (KCN) and pharmacological inhibitor ADDA5. Exogenous oxidants were generated using cell culture medium that has been treated with the cold physical plasma effluent of an atmospheric pressure argon plasma jet (kINPen). This plasma-treated medium was subsequently applied to different cells. Metabolic activity was assessed by fluorescence quantification of resazurin-to-resorufin transformation. ATP levels were monitored by a luminescence assay. Total cell counts, intracellular ROS levels (DCF), mitochondria membrane potential (TMRE), cell membrane integrity (sytox green) and cellular morphology were quantitatively assessed using live cell and high throughput confocal imaging (Operatta; Perkin Elmer). For tumor cells, also 3D spheroid models were investigated for viability by sytox green staining. ADDA5, NaN3 and KCN treatment alone failed to induce a significant alteration in metabolic activity in cancer cells. We then exposed the cells pretreated with NaN3 (100-500 µM) or KCN (250-500 µM) to plasma-treated medium. There was a significant inhibition of metabolic activity and rapid induction of cell death 6 h following treatment in melanoma cells compared to cell receiving plasma-treated medium alone. Increase in cellular superoxide levels and decrease in mitochondrial membrane potential and ATP levels was observed preceding cell death. However, no caspase 3 cleavage was observed upon immunoblotting. siRNA mediated knockdown of COX4a led to increased sensitivity of tumor cells towards plasma-treated medium. Furthermore, we validated our findings using a pharmacological inhibitor of complex IV ADDA5 in a tumor spheroid model and demonstrated that complex IV inhibition supplemented with plasma-treated medium, triggered significant cell death via caspase independent mechanism in melanoma cells.

Effect of Sodium Treatment on the Performance of Electrostatic Spray Assisted Vapour Deposited Copper-poor Cu(In,Ga)(S,Se)2 Solar Cells

In our work, eco-friendly, non-vacuum and low cost Electrostatic Spray Assisted Vapour Deposition (ESAVD) method has been used to produce Cu(In,Ga)(S,Se)2 (CIGS) solar cells. Copper (Cu) deficient (Cu/In + Ga = 0.76) CIGS films were designed to avoid the rather dangerous KCN treatment step for the removal of conductive minor phases of Cu2S/Cu2Se. A simple sodium (Na) treatment method was used to modify the morphology and electronic properties of the absorber and it clearly improved the solar cell performance. The SEM and XRD results testified a slightly increase of the grain size and (112) crystal orientation in the Na-incorporated CIGS thin films. From the Mott-schottky results, it can be seen that the functions of the Na treatment in our non-vacuum deposited CIGS are mainly used for defect passivation and reduction of charge recombination. Photovoltaic characteristics and j-V curve demonstrated that the dipping of CIGS films in 0.2 M NaCl solution for 20 minutes followed by selenization at 550 °C under selenium vapor resulted in the optimum photovoltaic performance, with jsc, Voc, FF and η of the optimized solar cell of 29.30 mA cm−2, 0.564 V, 65.59% and 10.83%, respectively.

P–N Junction Passivation in Kesterite Solar Cells by Use of Solution-Processed TiO2 Layer

In this work, we used a solution-processed TiO2 layer between Cu2ZnSnSe4 and CdS buffer layer to reduce the recombination at the p–n junction. Introducing the TiO2 layer showed a positive impact on V OC but fill factor and efficiency decreased. Using a KCN treatment, we could create openings in the TiO2 layer, as confirmed by transmission electron microscopy measurements. Formation of these openings in the TiO2 layer led to the improvement of the short-circuit current, fill factor, and the efficiency of the modified solar cells.

植物根のシアン化物非感受性呼吸について(第1報) : KCN処理が, 呼吸・代謝に及ぼす影響

植物根のシアン化物非感受性呼吸について(第1報) : KCN処理が, 呼吸・代謝に及ぼす影響

Potassium-ion doped Cu(In,Ga)Se2 thin films solar cells: Phase formation, microstructures, and photovoltaic characteristics

A doping process of potassium-ion was adopted as an alternative to the toxic KCN etching used for the removal of Cu2-xSe compounds. The effects of potassium-ion doping on the phase formation and photovoltaic characteristics of the solution-coated Cu(In,Ga)Se2 films was investigated. As the incorporation of potassium ions was increased from 0 mol% to 1.0 mol%, the coexistent Cu2-xSe compounds were gradually reduced and the monophasic Cu(In,Ga)Se2 films were obtained. The potassium-ion doped Cu(In,Ga)Se2 films with dense and smooth morphology improved the coverage of CdS buffer layer and suppressed the additional shunt paths. Hence, the conversion efficiency of the solar cells fabricated without KCN treatment was significantly improved from 4.70%to 11.02%. Additionally, the diode factor (A) and the saturated current (J0) were reduced due to the suppression of carrier recombination and leakage current. Further increasing the content of potassium ions to 5.0 mol%, the oversupplied potassium ions reduced the grain size and induced the carrier recombination in the obtained films, thereby resulting in the deterioration of the cell performance. This investigation demonstrates that the incorporation of potassium ions into Cu(In,Ga)Se2 films with appropriated amounts can effectively diminish the formation of Cu2-xSe compounds, thereby improving the photovoltaic performance of the fabricated Cu(In,Ga)Se2 solar cells.

Time-resolved photoluminescence of Cu(In,Ga)(Se,S)2 thin films and temperature dependent current density-voltage characteristics of their solar cells on surface treatment effect

Influences of the surface treatments of Cu(In,Ga)(Se,S)2 (CIGSSe) thin films, which are KCN, HCl, or thiuorea treatments, were investigated by time-resolved photoluminescence (TRPL) and temperature dependent current density-voltage (J-V) characteristics of their solar cells. It is demonstrated that the KCN treatment optimized under 1 wt% leads to the significant increase in conversion efficiency (η) up to 19.21%. On the other hand, the η of the CIGSSe solar cells is in ranges of 13.70–15.51% and 9.86–10.70% with the HCl treatments (0.3–0.7 mol/L), and thiuorea treatments (0.5–1.5 mol/L), respectively, which are lower than 16.66% that of the reference solar cell without the surface treatment. According to TRPL measurements, the quality of near-surface CIGSSe is improved with the KCN treatment (1 wt%) owing to enhanced TRPL lifetimes, whereas that is deteriorated with the HCl and thiuorea treatments due to decreased TRPL lifetimes. In addition, according to the temperature-dependent J-V measurement, the interface recombination of the CIGSSe solar cell is decreased with the KCN treatment, while that of the CIGSSe solar cells is increased with the HCl and thiuorea treatments. Ultimately, 19.21%-efficient CIGSSe solar cell with the KCN treatment (1 wt%) at room temperature with the increased VOC of 0.692 V was obtained, which is around 15.3% relatively higher η than that of the solar cell without the surface treatment.

Radiation Promptly Alters Cancer Live Cell Metabolic Fluxes: An In Vitro Demonstration.

Quantitative data is presented that shows significant changes in cellular metabolism in a head and neck cancer cell line 30 min after irradiation. A head and neck cancer cell line (UM-SCC-22B) and a comparable normal cell line, normal oral keratinocyte (NOK) were each separately exposed to 10 Gy and treated with a control drug for disrupting metabolism (potassium cyanide; KCN). The metabolic changes were measured live by fluorescence lifetime imaging of the intrinsically fluorescent intermediate metabolite nicotinamide adenosine dinucleotide (NADH) fluorescence; this method is sensitive to the ratio of bound to free NADH. The results indicated a prompt shift in metabolic signature in the cancer cell line, but not in the normal cell line. Control KCN treatment demonstrated expected metabolic fluxes due to mitochondrial disruption. The detected radiation shift in the cancer cells was blunted in the presence of both a radical scavenger and a HIF-1α inhibitor. The HIF-1α abundance as detected by immunohistochemical staining also increased substantially for these cancer cells, but not for the normal cells. This type of live-cell metabolic monitoring could be helpful for future real-time studies and in designing adaptive radiotherapy approaches.

Reliable wet-chemical cleaning of natively oxidized high-efficiency Cu(In,Ga)Se2 thin-film solar cell absorbers

Currently, Cu-containing chalcopyrite-based solar cells provide the highest conversion efficiencies among all thin-film photovoltaic (PV) technologies. They have reached efficiency values above 20%, the same performance level as multi-crystalline silicon-wafer technology that dominates the commercial PV market. Chalcopyrite thin-film heterostructures consist of a layer stack with a variety of interfaces between different materials. It is the chalcopyrite/buffer region (forming the p-n junction), which is of crucial importance and therefore frequently investigated using surface and interface science tools, such as photoelectron spectroscopy and scanning probe microscopy. To ensure comparability and validity of the results, a general preparation guide for “realistic” surfaces of polycrystalline chalcopyrite thin films is highly desirable. We present results on wet-chemical cleaning procedures of polycrystalline Cu(In1-xGax)Se2 thin films with an average x = [Ga]/([In] + [Ga]) = 0.29, which were exposed to ambient conditions for different times. The hence natively oxidized sample surfaces were etched in KCN- or NH3-based aqueous solutions. By x-ray photoelectron spectroscopy, we find that the KCN treatment results in a chemical surface structure which is – apart from a slight change in surface composition – identical to a pristine as-received sample surface. Additionally, we discover a different oxidation behavior of In and Ga, in agreement with thermodynamic reference data, and we find indications for the segregation and removal of copper selenide surface phases from the polycrystalline material.

Influence of Cu(In,Ga)(Se,S)2 surface treatments on the properties of 30 × 30 cm2 large area modules with atomic layer deposited Zn(O,S) buffers

We report the effect of Cu(In,Ga)(Se,S)2 absorber surface treatments on the properties of atomic layer deposited-Zn(O,S) buffered 30×30cm2 large area modules. The absorber is prepared by the sequential process. H2O and KCN solution treatments are investigated. The absorber surface treatment is found to influence significantly the open circuit voltage and the fill factor of the full modules. Light soaking related metastabilities are also found to depend on the type of treatment. While both H2O and KCN treatments are efficient at removing Se-oxides and Na2HCO3, the KCN treatment is found to remove additionally Ga-oxides and elemental Se that are detected on the surface of the absorber. A 30×30cm2 module aperture efficiency up to 12.3% could be achieved with KCN surface treatment of the absorber.

Effect of KCN Treatment on Cu-Se Secondary Phase of One-step Sputter-deposited CIGS Thin Films Using Quaternary Target

The structural, optical and electrical properties of sputter-deposited CIGS films were directly influenced by the sputtering process parameters such as substrate temperature, working pressure, RF power and distance between target and substrate. CIGS thin films deposited by using a quaternary target revealed to be Se deficient due to Se low vapor pressure. This Se deficiency affected the overall stoichiometry of the films, causing the films to be Cu-rich. Current tends to pass through the Cu-Se channels which act as the shunting path increasing the film conductivity. The crystal structure of CIGS thin films depends on the substrate orientation due to the influence of surface morphology, grain size and stress of Mo substrate. The excess of Cu was removed from the CIGS films by KCN treatment, achieving a suitable Cu concentration (referred as Cu-poor) for the fabrication of solar cell. Due to high Cu concentrations on the CIGS film surface induced by Cu-Se phases after CIGS film deposition, KCN treatment proved to be necessary for the fabrication of high efficiency solar cells. Also during KCN treatment, dislocation density and lattice parameter decreased as excess Cu was removed, resulting in increase of bandgap and the decrease of conductivity of CIGS films. It was revealed that Cu-Se secondary phase could be removed by KCN wet etching of CIGS films, allowing the fabrication of high efficiency absorber layer.