Papers by Diego Colombara
Journal of materials chemistry. A, Materials for energy and sustainability, Dec 31, 2022
Proceedings of SPIE, Sep 23, 2016
Thin films of Cu2GeS3 are grown by annealing copper layers in GeS and S gaseous atmosphere above ... more Thin films of Cu2GeS3 are grown by annealing copper layers in GeS and S gaseous atmosphere above 460°C. Below 500°C the cubic polymorph is formed, having inferior optoelectronic properties compared to the monoclinic phase, formed at higher temperature. The bandgap of the cubic phase lies below that of the monoclinic phase: they are determined from absorption measurements to be 1.23 and 1.55 eV respectively. Photoluminescence measurements are performed and only the monoclinic Cu2GeS3 shows a photoluminescence signal with a peak maximum at 1.57 eV. We attribute this difference between cubic and monoclinic to the higher quasi fermi level splitting of the monoclinic phase. Wavelength dependent photoelectrochemical measurements demonstrate the Cu2GeS3 to be p-type with an apparent quantum efficiency of less than 3 % above the band gap.
ECS transactions, Apr 13, 2015
ABSTRACT
Advanced Energy Materials
Chemistry of Materials, 2021
The encapsulation of colloidal lead halide perovskite nanocrystals within silica (SiO 2) is one o... more The encapsulation of colloidal lead halide perovskite nanocrystals within silica (SiO 2) is one of the strategies to protect them from polar solvents and other external factors. Here, we demonstrate the overcoating of CsPbBr 3 perovskite nanocrystals with silica by exploiting the anhydride-induced transformation of Cs 4 PbBr 6 nanocrystals. CsPbBr 3 @SiO 2 core−shell nanocrystals are obtained after (i) a reaction between colloidal Cs 4 PbBr 6 nanocrystals and maleic anhydride in toluene that yields CsPbBr 3 nanocrystals and maleamic acid and (ii) a silica-shell growth around CsPbBr 3 nanocrystals via hydrolysis of added alkoxysilanes. The reaction between Cs 4 PbBr 6 nanocrystals and maleic anhydride is necessary to promote shell formation from alkoxysilanes, as demonstrated in control experiments. The best samples of asprepared CsPbBr 3 @SiO 2 nanocrystals consist of ∼10 nm single-crystal CsPbBr 3 cores surrounded by ∼5−7 nm amorphous silica shell. Despite their core−shell structure, such nanostructures are poor emitters and degrade within minutes of exposure to ethanol. The photoluminescence intensity of the core−shell nanocrystals is improved by the treatment with a solution of PbBr 2 and ligands, and their stability in ethanol is extended to several days after applying an additional silica growth step. Overall, the investigated approach outlines a strategy for making colloidal core−shell nanocrystals utilizing the transformative chemistry of metal halides and reveals interesting insights regarding the conditions required for CsPbBr 3 @SiO 2 nanocrystal formation.
Chemistry of Materials, Dec 13, 2013
2022 IEEE 49th Photovoltaics Specialists Conference (PVSC)
ACS Applied Materials & Interfaces, 2021
Cadmium-free buffer layers deposited by a dry vacuum process are mandatory for low-cost and envir... more Cadmium-free buffer layers deposited by a dry vacuum process are mandatory for low-cost and environmentally friendly Cu(In1-xGax)Se2 (CIGS) photovoltaic in-line production. Zn(O,S) has been identified as an alternative to the chemical bath deposited CdS buffer layer, providing comparable power conversion efficiencies. Recently, a significant efficiency enhancement has been reported for sputtered Zn(O,S) buffers after an annealing treatment of the complete solar cell stack; the enhancement was attributed to interdiffusion at the CIGS/Zn(O,S) interface, resulting in wide-gap ZnSO4 islands formation and reduced interface defects. Here, we exclude interdiffusion or island formation at the absorber/buffer interface after annealing up to 200 °C using high-resolution scanning transmission electron microscopy (HR-STEM) and energy-dispersive X-ray spectroscopy (EDX). Interestingly, HR-STEM imaging reveals an epitaxial relationship between a part of the Zn(O,S) buffer layer grains and the CIGS grains induced by annealing at such a low temperature. This alteration of the CIGS/buffer interface is expected to lead to a lower density of interface defects, and could explain the efficiency enhancement observed upon annealing the solar cell stack, although other causes cannot be excluded.
The synthesis of morphologically good thin chalcogenide films via the two-stage route is a chemic... more The synthesis of morphologically good thin chalcogenide films via the two-stage route is a chemical challenge. The reactivity towards the chalcogen-bearing reactants of the different metals within the precursor film is a trade-off between thermodynamic driving force and kinetics of binary sulfide formation. In this work, CuSbS2 and Cu3BiS3 thin films were produced by conversion of stacked and co-electroplated metal precursor layers in the presence of elemental sulfur vapour. Ex-situ XRD and SEM/EDS analyses of RTP treated samples were employed to study the reaction sequence and create ‘‘Time-Temperature-Reaction’’ diagrams for the description of the reaction kinetics. Modified Pilling–Bedworth coefficients were introduced for the interpretation of the experimental results. The chalcogenizing conditions have a strong influence on the following aspects: (1) Extent of intermediate phase segregation and/or crystallite size (2) Thermodynamic (de)stabilization at low temperature (3) Therm...
physica status solidi (RRL) – Rapid Research Letters
This work was partially supported by the European Union's Horizon 2020 research and innovatio... more This work was partially supported by the European Union's Horizon 2020 research and innovation program under grant agreement No. 641004 (project Sharc25). The authors acknowledge additional support by the Spanish project AIC‐B‐2011‐0806, and by the “Micro‐concentrator thin film solar cells (MiconCell)” project (028922) and the “Correlated Analysis of Inorganic Solar Cells in and outside an Electron Microscope (CASOLEM)” project (028917), both co‐funded by FCT and ERDF through COMPETE2020. DC acknowledges the European Commission for funding the NanoTrainforGrowth II project No. 713640 through the Marie Curie Cofund programme.
Electrochemistry Communications
This study explores the rich chemistry of elemental selenium reduction to monoselenide anions. Th... more This study explores the rich chemistry of elemental selenium reduction to monoselenide anions. The simplest possible homogeneous electron transfer occurs with free electrons, which is only possible in plasmas; however, alkali metals in liquid ammonia can supply unbound electrons at much lower temperatures, allowing in situ analysis. Here, solvated electrons reduce elemental selenium to K 2 Se, a compound relevant for alkali metal doping of Cu(In,Ga)Se 2 solar cell material. It is proposed that the reaction follows pseudo first-order kinetics with an inner-sphere or outer-sphere oxidation semi reaction mechanism depending on the concentration of solvated electrons.
Nature communications, Feb 26, 2018
Copper indium gallium diselenide-based technology provides the most efficient solar energy conver... more Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Sefilms, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSegrown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Seand Cu(In,Ga)Sephase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to...
Electrochemistry Communications, 2014
The quality control of individual semiconductor thin films during fabrication of multiple layers ... more The quality control of individual semiconductor thin films during fabrication of multiple layers is important for industry and academia. The ultimate aim of this research is to predict the efficiency of p-n junction solar cells by photoelectrochemical analysis of the bare p-type semiconductor. A linear correlation between the photocurrent measured electrochemically on Cu(In,Ga)Se 2 absorber layers through a Eu 3+ electrolyte junction and short circuit current and efficiency of the corresponding solid state devices is found. However, the correlation is complicated by pronounced recombination at the semiconductor/electrolyte interface, while the solid state interface behaves more ideally.
RSC Energy and Environment Series, 2014
ABSTRACT
Thin Solid Films, 2011
Due to the availability and low cost of the elements, the ternary Cu-Sb-S and Cu-Sb-Se semiconduc... more Due to the availability and low cost of the elements, the ternary Cu-Sb-S and Cu-Sb-Se semiconductor systems are being studied as sustainable alternative absorber materials to replace CuIn(Ga)(S,Se) 2 in thin film photovoltaic applications. Simple evaporation of the metal precursors followed by annealing in a chalcogen environment has been employed in order to test the feasibility of converting stacked metallic layers into the desired compounds. Other samples have been produced from aqueous solutions by electrochemical methods that may be suitable for scale-up. It was found that the minimum temperature required for the complete conversion of the precursors into the ternary chalcogen is 350 °C, while binary phase separation occurs at lower temperatures. The new materials have been characterized by structural, electrical and photoelectrochemical techniques in order to establish their potential as absorber layer materials for photovoltaic applications. The photoactive films consisting of CuSbS 2 and CuSbSe 2 exhibit band-gap energies of ~1.5eV and ~1.2 eV respectively, fulfilling the Shockley-Queisser requirements for the efficient harvesting of the solar spectrum.
Solar Energy Materials and Solar Cells, 2014
Supporting information Implementation of 3D model for generation of simulated EQE spectra The EQE... more Supporting information Implementation of 3D model for generation of simulated EQE spectra The EQE can be simulated from EQE R taking into account the filtering of photons through ZnSe and the collection losses of charge carriers in the absorber layer underneath ZnSe. To consider the collection losses it is necessary to compute the total volume of absorber layer underneath ZnSe and the fraction of it which is still subject to carrier collection.
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Papers by Diego Colombara