A new approach for alkali incorporation in Cu2ZnSnS4 solar cells

The addition of alkali elements has become mandatory for boosting solar cell performance in chalcogenide thin films based on kesterites (Cu2ZnSnS4, CZTS). A novel doping process is presented here, that consists in the incorporation of sodium or lithium during the deposition of the CdS buffer layer, followed by a post-deposition annealing (PDA). As the doping route leads to more efficient devices in comparison with the undoped reference sample, the influence of PDA temperature was also investigated. Compositional profiling techniques, time-of-flight secondary ion mass spectrometry (TOF-SIMS) and glow discharge optical mission spectroscopy (GDOES), revealed a dependence of the alkaline distribution in kesterites with the PDA temperature. Although the doping process is effective in that it increases the alkaline concentration compared to the undoped sample, the compositional profiles indicate that a significant proportion of Li and Na remains ‘trapped’ within the CdS layer. In the 200 °C-300 °C range the alkali profiles registered the higher concentration inside the kesterite. Despite this, an additional alkali accumulation close to the molybdenum/fluorine doped tin oxide substrate was found for all the samples, which is frequently related to alkali segregation at interfaces. The addition of both, lithium and sodium, improves the photovoltaic response compared to the undoped reference device. This is mainly explained by a substantial improvement in the open-circuit potential (V oc) of the cells, with best devices achieving efficiencies of 4.5% and 3% for lithium and sodium, respectively. Scanning-electron microscopy images depicted a ‘bilayer structure’ with larger grains at the top and small grains at the bottom in all samples. Moreover, the calculated bandgap energies of the CZTS films account for changes in the crystallographic order-disorder of the kesterites, more related to the PDA treatment rather than alkali incorporation. Even if further optimization of the absorber synthesis and doping process will be required, this investigation allowed the evaluation of a novel strategy for alkali incorporation in kesterite based solar cells.Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Hernandez, A.. Catalonia Institute For Energy Research Irec; EspañaFil: Sánchez, Y.. Catalonia Institute For Energy Research Irec; EspañaFil: Fonoll, R.. Catalonia Institute For Energy Research Irec; EspañaFil: Placidi, M.. Universidad Politécnica de Catalunya; España. Catalonia Institute For Energy Research Irec; EspañaFil: Izquierdo, V.. Catalonia Institute For Energy Research Irec; EspañaFil: Cabas Vidani, A.. Swiss Federal Laboratories for Materials Science and Technology; SuizaFil: Valentini, M.. Enea Centro Ricerche Casaccia; ItaliaFil: Mittiga, A.. Enea Centro Ricerche Casaccia; ItaliaFil: Pistor, P.. Universidad Pablo de Olavide; EspañaFil: Malerba, C.. Enea Centro Ricerche Casaccia; ItaliaFil: Saucedo, E.. Universidad Politécnica de Catalunya; Españ

Solution-based synthesis of kesterite thin film semiconductors

Large-scale deployment of photovoltaic modules is required to power our renewable energy future. Kesterite, Cu2ZnSn(S, Se)4, is a p-type semiconductor absorber layer with a tunable bandgap consisting of earth abundant elements, and is seen as a potential 'drop-in' replacement to Cu(In,Ga)Se2 in thin film solar cells. Currently, the record light-to-electrical power conversion efficiency (PCE) of kesterite-based devices is 12.6%, for which the absorber layer has been solution-processed. This efficiency must be increased if kesterite technology is to help power the future. Therefore two questions arise: what is the best way to synthesize the film? And how to improve the device efficiency? Here, we focus on the first question from a solution-based synthesis perspective. The main strategy is to mix all the elements together initially and coat them on a surface, followed by annealing in a reactive chalcogen atmosphere to react, grow grains and sinter the film. The main difference between the methods presented here is how easily the solvent, ligands, and anions are removed. Impurities impair the ability to achieve high performance (>∼10% PCE) in kesterite devices. Hydrazine routes offer the least impurities, but have environmental and safety concerns associated with hydrazine. Aprotic and protic based molecular inks are environmentally friendlier and less toxic, but they require the removal of organic and halogen species associated with the solvent and precursors, which is challenging but possible. Nanoparticle routes consisting of kesterite (or binary chalcogenides) particles require the removal of stabilizing ligands from their surfaces. Electrodeposited layers contain few impurities but are sometimes difficult to make compositionally uniform over large areas, and for metal deposited layers, they have to go through several solid-state reaction steps to form kesterite. Hence, each method has distinct advantages and disadvantages. We review the state-of-the art of each and provide perspective on the different strategies.Fil: Todorov, I. T.. IBM Research. Thomas J. Watson Research Center; Estados UnidosFil: Hillhouse, H. W.. University of Washington; Estados UnidosFil: Aazou, S.. Mohammed V University; MarruecosFil: Sekkat, Z.. Mohammed V University; MarruecosFil: Vigil Galán, O.. National Polytechnic Institute; MéxicoFil: Deshmukh, S. D.. Purdue University; Estados UnidosFil: Agrawal, R.. Purdue University; Estados UnidosFil: Bourdais, S.. No especifíca;Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Arnou, P.. University Of Luxembourg; LuxemburgoFil: Mitzi, D.B.. University of Duke; Estados UnidosFil: Dale, P.. University Of Luxembourg; Luxemburg

Composition, morphology, and optical properties of CuInSe2 thin films electrodeposited using constant and pulsed potentials

CuInSe2 thin films were electrodeposited on conductive glass using potentiostatic (PoED) and pulsed electrodeposition (PuED). One pulse consisted of a step between two potential values: E10-0.9 and E20-0.1 VSCE. Each potential was applied during 10 s. Twenty to 180 pulses were applied. In the case of PoED, -0.9 VSCE were applied during 400 to 3,600 s. The differences in crystallographic structure, morphology, and chemical composition between as-deposited PoED and PuED films were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy dispersive scanning spectroscopy. The presence of secondary phases seemed to be reduced by using PuED. X-ray diffraction showed no significant differences between films prepared by PuED and PoED. Instead, micro-Raman spectroscopy revealed that the chemical composition and homogeneity were improved by pulsing the potential. The thickness of the films increased, and the crystallinity improved as more pulses were applied. For both types of electrodeposition, longer times favored the formation of nearly stoichiometric CuInSe2. For the electrical characterization, the films were annealed in argon and then etched in a KCN solution. KCN etching showed no effect in the film composition. Photoelectrochemical tests and I-V curves confirm p-type conduction. The differences observed in composition, morphology, and optoelectronic properties were attributed to the current profile imposed on the electrode.Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Deposición de CuInS2 y CuInSe2 para su aplicación en celdas solares: Síntesis, caracterización y ensamblado de dispositivos fotovoltaicos

Una de las fuentes de energía alternativa con mayor proyección son los dispositivos fotovoltaicos, que utilizan la conversión directa de energía solar en energía eléctrica. El obtáculo más importante para la implementación de las celdas solares fotovoltaicas a gran escala es el costo de los módulos fotovoltaicos. Una parte sustancial de los costos totales de producción para los módulos fotovoltaicos es el costo de los materiales  y de producción de las celdas fotovoltaicas. En forma permanente están siendo desarrolladas nuevas arquitecturas basadas en nanomateriales y películas delgadas, con el objetivo de producir celdas solares eficientes, de bajo costo y amigables con el medio ambiente El objetivo de esta investigación fue la obtención de los semiconductores tipo n y p, que forman la celda solar, empleando principalmente técnicas de que no requieren vacío, como rocío pirolítico y electrodeposición. El trabajo se focaliza principalmente en la obtención de películas delgadas de dos materiales que han despertado grán interés en los últimos años.: dióxido de titanio (TiO2) y calcopiritas de cobre e indio (CuInSe2 y CuInS2).Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Pulsed electrodeposition of p-type CuInSe2 thin films

CuInSe2 thin films have been electrodeposited on conductive glass using cyclic pulse electrodeposition. One cycle consists of consequtively applying potentials E1 and E2, each during 10 s and a total of 90 cycles are applied. E1 is chosen between -0.7 and -0.9 VSCE while E2 is fixed at -0.1 VSCE. The films are annealed in argon and then etched in KCN solution to eliminate remnant secondary phases. The material is characterized employing grazing incident X-rays diffraction, Raman spectroscopy, scanning electron microscopy and energy dispersive scanning spectroscopy. The presence of secondary phases seems to be reduced when compared to films prepared at fixed potentials. The films are crystalline and the overall quality improves by annealing in Ar. Photoelectrochemical tests, Mott-Schottky plots and I-V curves confirm p-type conduction. The diffusion regime imposed by the potential pulses could be responsible for the different morphology and composition of samples prepared with pulsed and potentiostatic electrodeposition.Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Spray deposition of Cu2ZnSnS4 thin films

Thin films of Cu2ZnSnS4 (CZTS) have been deposited on top of glass substrates using spray pyrolysis and aqueous precursors. The substrate temperatures ranged from 325 to 425 ºC. The effect of a thermal treatment in sulfur vapor on the structural, morphological, and optical properties of CZTS films have been studied. X-ray diffractograms revealed the formation of polycrystalline CZTS films, where the crystalline degree increased with substrate temperature and with the use of sulfur during annealing. Raman maps show a homogenous distribution of the CZTS phase along the analyzed surface and a random distribution of a CuXS binary phase. Raman signals attributed to this secondary phase seem to be reduced after sulfurization. Band gap values vary between 1.3 and 1.5 eV. The sulfurization treatment has no significant effect on the composition of the deposits or on the band gap energy value. However, the crystallite size increased after annealing in sulfur. Films deposited at 425 ºC presented a nearly stoichiometric composition, suitable optical properties and p-type conductivity. These materials are suitable for absorbent layers in solar cell fabrication, even in the asdeposited condition.Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Santoro, G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Electrodeposition of CuInSe2 and In2Se3 on flat and nanoporous TiO2 substrates

In2Se3 and CuInSe2 films have been prepared by potentiostatic electrodeposition from deareated aqueous solutions. The substrate consisted of a duplex layer of dense and nanoporous TiO2 obtained by spray pyrolysis deposition (SPD) and doctor blading. In2Se3 thin films are electrodeposited in between the TiO2/CuInSe2 pn heterojunction to block the electron back flow and lower the interfacial recombination produced upon illumination. The films have been characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and optical transmission. Annealing the samples in Se atmosphere is essential to improve the crystallinity of the In2Se3 and CuInSe2 films. The combination of TiO2/In2Se3/CuInSe2 shows very good diode behavior with a rectification ratio higher than 100 at ±1 V.Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Goossens, A.. Delft University of Technology; Países Bajo

Sulfurization of electrodeposited CuInSe2-based solar cells

CuInSe2 (CISe) thin films have been prepared by single-step electrodeposition on top of TCO/TiO2 and TCO/TiO2/In2S3 coated electrodes. TiO2 and In2S3 have been deposited by spray–pyrolysis. The electrodeposition step is studied using cyclic voltammetry in an acidic electrolyte. Electrodeposited CISe is then subjected to two different thermal treatments. The first treatment is an annealing step under argon atmosphere, carried out to enhance the crystallinity of the film. The second consists of a sulfurization process, where sulfur is vaporized and mixed with the argon flux, leading to substantial changes in the composition of the chalcogenide. The crystallinity, morphology and stoichiometry of the annealed films are characterized by XRD, micro-Raman spectroscopy and SEM/EDX. Raman spectra and EDX show an almost complete replacement of the Se atoms by S atoms. Etching the films in KCN solution is a key step, enabling a final adjustment in the stoichiometry. The incorporation of In2S3 buffer layer in TiO2/CuIn(SeS)2 solar cells produces a marked improvement in the cell efficiency. Despite this improvement, the values of Jsc and the fill factor (FF) are relatively low, showing efficiencies below 1%, most likely associated to the resistances present in the multi-layered cell.Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Goossens, Alain. Delft University of Technology; Países BajosFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Cu 2 ZnSnS 4 Electrodeposition by Sulfurization of Metallic Precursors

This work describes the electrodeposition of a Cu-Zn-Sn precursoron conducting glass that transforms into Cu2ZnSnS4 during a heattreatment at 500 °C in vaporized sulfur. Citrate and hydroxylconcentrations were adjusted to fix the pH value in 5.9, so thatCu2ZnSnS4 could be deposited on top of ZnO in solar cells built insuperstrate configuration. The deposits were characterized by X-raydiffraction, Raman spectroscopy, scanning electronic microscopy,UV-Vis spectroscopy and photoelectrochemical techniques.Cu2ZnSnS4 films obtained with short electrodeposition times aregood-quality, p-type absorbers suitable to be used in kesterite thinfilms solar cells. The most promising results were obtained using 0.1mol L-1 sodium citrate, which is attributed to a higher Zn content inthe precursor deposit.Fil: Perelstein, Gonzalo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Different Routes of Fixed pH to Electrodeposit Cu2ZnSnS4 for Photovoltaic Devices

Cu2ZnSnS4 films have been prepared by sulfurizing ternary and quaternary precursors electrodeposited on conducting glass. Citrate and hydroxyl concentrations were used to adjust the pH value in 5.9 and they produce deposits with different properties. The deposits were characterized by X-ray diffraction, multi-laser Raman spectroscopy, scanning electronic microscopy, energy-dispersive X-ray spectroscopy, UV?Vis spectroscopy and photoelectrochemical techniques. Raman spectroscopy and X-ray diffraction results confirmed the formation of crystalline CZTS after sulfurization. Photocurrent analysis confirmed the p-type nature of the semiconductor. Cu2ZnSnS4 films obtained with short electrodeposition times are good-quality absorbers suitable to be used in superstrate thin films solar cells. The bath composition together with the acidity level of the precursor bath needs to be adjusted together, in order to adequate the electrodeposition of Cu2ZnSnS4 to the characteristics of different substrates. The most promising results were obtained when using the lowest citrate concentration. This is likely related to the proportion of Zn in the precursor deposit. The incorporation of S to the precursor bath resulted in no particular benefit. This element is efficiently incorporated during annealing in sulfur vapor and seems to be detrimental for the morphology when present in the electrodeposition precursor bath.Fil: Perelstein, Gonzalo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin