Electronic effects of Cd on the formation of the CdS CuInS2 heterojunction

The possibility of doping and Fermi level pinning of CuInS2 thin layer solar cell absorbers caused by the diffusion of Cd into the absorber during junction formation via chemical bath deposition was investigated. The analysis of thin CdS layers deposited on CuInS2 showed the amount of deposition induced band bending on the CuInS2 surface position of the Fermi level in the respective bandgaps was not experimentally reproducible. However, the value of the valence band offset between the two materials was reproducible between different depositions within the error of the measurement. Thus, the deposition of the CdS does not lead to a consistent pinning position of the Fermi level in the CuInS2 CdS heterojunction. The removal of the CdS layers with HCl left a thin Cd containing layer on the CuInS2 surface and it was shown that this surface was not doped by the remaining Cd. Furthermore, the influence of the HCl of the CuInS2 was explored and found to form a reproducible surface richer in Cu than CuInS2 etched in potassium cyanide solution

Limitations of Near Edge X Ray Absorption Fine Structure as a tool for observing conduction bands in chalcopyrite solar cell heterojunctions

A non optimized interface band alignment in a heterojunctionbased solar cell can have negative eff ects on the current and voltage characteristics of the resulting device. To evaluate the use of Near Edge X ray Absorption Fine Structure spectroscopy NEXAFS as a means to measure the conduction band position, Cu In,Ga S2 chalcopyrite thin film surfaces were investigated as these form the absorber layer in solar cells with the structure ZnO Buffer Cu In,Ga S2 Mo Glass. The composition dependence of the structure of the conduction bands of CuInxGa1 xS2 has been revealed for x 0, 0.67 and 1 with both hard and soft NEXAFS and the resulting changes in conduction band off set at the junction with the bu ffer layer discussed. A comprehensive study of the positions of the absorption edges of all elements was carried out and the development of the conduction band with Ga content was observed, also with respect to calculated densities of state

Zn(O, S) layers for chalcoyprite solar cells sputtered from a single target

A simplified Cu(In, Ga)(S, Se)2/Zn(O, S)/ZnO:Al stack for chalcopyrite thin- film solar cells is proposed. In this stack the Zn(O, S) layer combines the roles of the traditional CdS buffer and undoped ZnO layers. It will be shown that Zn(O, S) films can be sputtered in argon atmosphere from a single mixed target without substrate heating. The photovoltaic performance of the simplified stack matches that of the conventional approach. Replacing the ZnO target with a ZnO/ZnS target may therefore be sufficient to omit the CdS buffer layer and avoid the associated complexity, safety and recycling issues, and to lower production cost

In vacuo XPS investigation of Cu In,Ga Se2 surface after RbF post deposition treatment

Latest record efficiencies of Cu In,Ga Se2 CIGSe solar cells were achieved by means of a rubidium fluoride RbF post deposition treatment PDT . To understand the effect of the RbF PDT on the surface chemistry of CIGSe and its interaction with sodium that is generally present in the CIGSe absorber, we performed an X ray photoelectron spectroscopy XPS study on CIGSe thin films as deposited by a three stage co evaporation process and after the consecutive RbF PDT. The sample transfer from the deposition to the XPS analysis chamber was performed via an ultra high vacuum transfer system. This allows to minimize air exposure, avoiding oxide formation on the CIGSe surface, especially for alkali treated absorbers. Beside an expected reduction of Cu and Ga content at the surface of RbF treated CIGSe films, we find that Rb penetrates the CIGSe and, contrary to fluorine, it is not completely removed by subsequent ammonia etching. The remaining Rb contribution at 110.0 amp; 8239;eV binding energy, which appears after the RbF PDT is similar to the one detected on a co evaporated RbInSe2 reference sample and together with a new Se 3d contribution may hence belong to an Rb In Se secondary phase on the CIGSe surface. In addition, Na is driven towards the surface of the CIGSe absorber as a direct result of the RbF PDT. This proves the ion exchange mechanism in the absence of moisture and air oxygen between heavy Rb atoms incorporated via PDT and lighter Na atoms supplied by the glass substrate. A remaining XPS signal of Na 1 amp; 8239;s is observed after etching the vacuum transferred RbF CIGSe sample, indicating that Rb and or F are not as much a driving force for Na as oxygen usually i

Cu In,Ga Se2 surface treatment with Na and NaF A combined photoelectron spectroscopy and surface photovoltage study in ultra high vacuum

Either metallic Na or NaF were deposited onto Cu In,Ga Se2 surfaces and studied by photoelectron spectroscopy and surface photovoltage spectroscopy without breaking the ultra high vacuum. The deposition of elemental Na at room temperature led to the formation of an intermediate Cu and Ga rich layer at the CIGSe surface, whereas for NaF the composition of the CIGSe surface remained unchanged. A metal like surface induced by an inverted near surface region with a reduced number of defect states was formed after the deposition of Na. Under the chosen experimental conditions, the near surface layer was independent on the amount of Na and stable in time. In contrast, the usage of NaF weakened the inversion and led to an increased band bending compared to the untreated CIGSe sample. The SPV signals decreased with proceeding time after the deposition of NaF

Molecularly imprinted conductive polymers for controlled trafficking of neurotransmitters at solid–liquid interfaces

We realize a molecularly imprinted polymer (MIP) which is imprinted with the retinal neurotransmitter glutamate. The films prepared by electrochemical deposition have a smooth surface with a granular morphology as observed using an atomic force microscope. Multiple reflection attenuated total reflection infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to chemically confirm the imprint of a neurotransmitter in the MIP at the solid–liquid and the solid–air interface, respectively. Fluorescence spectroscopy using the dye fluorescamine is used to monitor the changes in neurotransmitter concentration in various solvents induced by application of voltage to the MIP. By controlling neurotransmitter trafficking across a solid–liquid interface with voltage, we suggest the possibility of using such a neurotransmitter imprinted MIP for chemical stimulation of retinal neurons. The current state of the art approach to restore sight in certain cases of blindness is the replacement of damaged photoreceptors by a subretinal implant consisting of light-sensitive photodiodes. Thus a future perspective of our work would be to chemically stimulate the neurons by replacing the photodiodes in the subretinal implant by the neurotransmitter imprinted polymer film

Correction Hierarchically structured iron doped silver Ag Fe lotus flowers for an efficient oxygen reduction reaction

The development of cheap and efficient electrocatalysts for the oxygen reduction reaction ORR is vital for the immediate commercialization of fuel cells which are still limited by the high cost and low performance of the utilized commercial Pt based electrodes. As a promising alternative, this study reports on the synthesis of hierarchical iron doped silver lotus flowers AgFelotus by a facile chemical procedure as robust and efficient ORR electrocatalysts. Succinic acid was used as a structure directing agent to tune the morphology of undoped and iron doped silver particles. In the absence of succinic acid, ball like silver particles were obtained, while using 2 mM succinic acid led to peony like flower structures. The doping of silver peony flowers with iron resulted in lotus like flower structures with high electrocatalytic activity for ORR together with outstanding tolerance against poisoning with various hydrocarbon HC impurities, in situ generated during fuel cell operation, as well as different fuels from anodic crossover. AgFelotus exhibited a superior ORR activity with more than 40 times higher stability than the commercial Pt C catalyst in alkaline media. This substantial performance enhancement is attributed to the unique lotus like flower structures providing more electroactive surface sites, in addition to the iron dopants which facilitate ORR charge transfe

Depth profile analyses of films grown at different temperatures

Cu(In,Ga)Se2films are used as absorber layers in chalcopyrite thin filmsolar cells. As the gallium concentration in the absorber can be used to control the band gap, there have been many efforts to vary the gallium concentration in depth to gain an optimum balance of light absorption, carrier collection, and recombination at different depths of the absorber film, leading to improved quantum efficiency. In this study, we investigate the effect of the maximum substrate temperature during film growth on the depth dependent gallium concentration. For the in-depth gallium concentration analyses, we use two techniques, covering complementary depth ranges. Angle dependent soft x-ray emission spectroscopy provides access to information depths between 20 and 470 nm, which covers the depth range of the space charge region, where most of the photoexcited carriers are generated. Therefore, this depth range is of particular interest. To complement this investigation we use secondary neutral mass spectrometry, which destructively probes the whole thickness of the absorber (≈2 μm). The two methods show increasingly pronounced gallium and indium gradients with decreasing maximum substrate temperature. The probing of the complementary depth ranges of the absorbers gives a consistent picture of the in-depth gallium distribution, which provides a solid basis for a comprehensive discussion about the effect of a reduced substrate temperature on the formation of gallium gradients in Cu(In,Ga)Se2 and the device performance of the corresponding reference solar cells

Green light photoelectrocatalysis with sulfur-doped carbon nitride : using triazole-purpald for enhanced benzylamine oxidation and oxygen evolution reactions

Novel high performing materials will dictate the pace of reinventing industrial chemical processes to attain desired carbon neutrality targets. Regarding the urgency of exploiting solar irradiation long range visible-light photoelectrocatalysts from abundant resources will play a key role in the aforementioned effort. Anionic doping via co-polymerization and pre-organization of precursors results in tuneable and extrinsic semiconductors, making this a highly attractive methodology. Triazole derivative-purpald, an unexplored precursor but sulfur (S) container, combined with melamine during one solid-state polycondensation reaction with two thermal steps leads to S-doped carbon nitrides (C34). The series of S-doped/CN4-based materials demonstrated enhanced optical, electronic, structural, geometric, textural, and morphological properties and exhibited higher performance in organic benzylamine photooxidation, oxygen evolution, and similar storing energy (capacitor brief investigation) than references. Among the five composites, 50M-50P exhibited the highest photooxidation conversion yield (84±3%) of benzylamine to imine at 535 nm – green light for 48h, due to an extra discrete shoulder reaching ~700 nm, an unusual high sulfur content, preservation of crystal size, new intraband energy states, rare deep structural defects by layer distortion, hydrophobic surface, low porosity, and 10-16 nm pores. An in-depth analysis of S doping was investigated coupling x-ray photoelectron spectroscopy, transmission electron microscope, and elemental analysis, providing insights on bonds, distribution, and surface/bulk content. This work contributes to the development of amorphous photocatalysts with long-visible-light range for solar energy conversion and storage