Preparation of Cu(In,Ga)Se2 photovoltaic absorbers by an aqueous metal selenite co-precipitation route

In this paper, we report a novel and simple solution-based approach for the fabrication of chalcopyrite Cu(In,Ga)Se2 thin film solar cells. An aqueous co-precipitation method based on metal selenites, M2(SeO3)x (M = Cu, In, Ga) precursors was investigated. The resulting powder, dispersed in a binder to form an ink, was coated on a substrate by doctor blade technique. A soft annealing treatment allowed the reduction of metal selenites into selenides. Further rapid thermal processing (RTP) achieved crystalline chalcopyrite absorber. The obtained layer provides good compositional control and adequate morphology for solar cell applications. The water-based synthesis is a sustainable and simple procedure, and together with doctor blade printing, provides a potential cost-effective advantage over conventional fabrication processes (vacuum-based deposition techniques). The short circuit current (JSC), open circuit voltage (VOC), fill factor (FF), and total area power conversion efficiency (Eff.) of the device are 26 mA/cm2, 450 mV, 62%, and 7.2%, respectively. The effective band gap of 1.12 eV confirmed Ga-incorporation in the CIGS crystal lattice.This work was supported by the Spanish Ministry of Science and Competiveness under INNPACTO Program (IPT-2011-0913- 920000). The authors would like to thanks to Manuel Ocana Jurado ~ (ICMS-CISC) for his help in the XPS measurements. L. Oliveira would like to thank the support of the National Council for Scientific and Technological Development (CNPq) e Brazil

Size- and density-controlled deposition of Ag nanoparticle films by a novel low-temperature spray chemical vapour deposition method—research into mechanism, particle growth and optical simulation

Ag nanoparticles have attracted interest for plasmonic absorption enhancement of solar cells. For this purpose, well-defined particle sizes and densities as well as very low deposition temperatures are required. Thus, we report here a new spray chemical vapour deposition method for producing Ag NP films with independent size and density control at substrate temperatures even below 100 °C, which is much lower than for many other techniques. This method can be used on different substrates to deposit Ag NP films. It is a reproducible, low-cost process which uses trimethylphosphine (hexafluoroacetylacetonato) silver as a precursor in alcoholic solution. By systematic variation of deposition parameters and classic experiments, mechanisms of particle growth and of deposition processes as well as the low decomposition temperature of the precursor could be explained. Using the 3D finite element method, absorption spectra of selected samples were simulated, which fitted well with the measured results. Hence, further applications of such Ag NP films for generating plasmonic near field can be predicted by the simulation

Organische Salze Sulfid- und Selenid-basierter Anionen: Bausteine für die Materialsynthese bi- und multinärer Metallchalkogenide

Eine Reihe organischer Salze mit chalkogenbasierten Anionen mit bisher unzugänglichen Kation-Anion Kombinationen wird beschrieben, zusammen mit deren Festkörperstrukturen und deren Eigenschaften in Lösung. Mögliche Wege zur Herstellung chalkogenbasierter Photovoltaikmaterialien CIGS und CZTS über Metallatkomplexe Cat[M(ESiMe3)(n+1)] werden beschrieben. Diese Metallatkomplexe wurden für M = Ga, In, Zn, Sn, Cu, Ag, Au realisiert (Cat = organisches Kation). Neben den Festkörperstrukturen dieser neuartigen Metallatsalze wurden thermischer Zerfall und spektroskopische Eigenschaften näher untersucht

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

Solution processing of thin films for solar cell applications: CuIn(S,Se)2, Cu(In,Ga)(S,Se)2 and ZnO:Al

Cu(In,Ga)(Se,S)2 (CIGS) solar cells have attracted a lot of attention due to their high performance and the prospect for lower manufacturing costs over conventional crystalline silicon solar cells. All recent record efficiency CIGS absorbers have been deposited using vacuum processing which introduces high manufacturing costs. CIGS can also be compatible with low cost, atmospheric processing which can significantly reduce manufacturing costs. Recently, there has been some progress in developing atmospheric solution-based processes for CIGS. Among different solution approaches, deposition of molecular precursors can be advantageous in terms of simplicity and straightforward compositional control. Nonetheless, the developed methodologies involve highly toxic reagents or large impurity content in the device, limiting the potential for commercialisation. This thesis describes the development of a novel solution-based approach for the deposition of CIGS absorber layers. Metal chalcogenides are used as the starting precursors, which are free from detrimental impurities. These compounds contain strong covalent bonds and, consequently, they are insoluble in common solvents. Until recently, hydrazine, which is highly toxic and explosive, was the only solvent to effectively dissolve these types of precursors, limiting the feasibility of this approach for industrial applications. In this work, metal chalcogenides are dissolved in a safer solvent combination of 1,2-ethanedithiol and 1,2-ethylenediamine, completely eliminating hydrazine from the process. By using this solvent system, optically transparent solutions are formed which exhibit long-term stability. The precursor solutions are decomposed cleanly and they are converted to single phase CIGS upon selenisation. CuIn(S,Se)2 solar cells with power conversion efficiencies up to 8.0% were successfully fabricated by spray depositing the precursor solution, followed by a selenisation step. This progress has been made by continuously optimising the deposition, drying, and especially the selenisation configuration. Among other parameters, the working pressure during selenisation was found to have a dramatic effect on the material crystalline quality. Rapid thermal processing was also explored as an alternative selenisation configuration to tube furnace annealing and it was shown to improve the back contact/absorber interface. It has been demonstrated that Ga can easily be incorporated in the absorber for band-gap tuning and, consequently, for VOC enhancement of the solar cells. The structural properties of the films were investigated with Ga content, as well as the opto-electronic characteristics of the corresponding solar cells. The band-gap of the material was conveniently varied by simply adjusting the precursor ratio, allowing for fine compositional control. By using this technique, Cu(In,Ga)(Se,S)2 solar cells with conversion efficiencies of up to 9.8% were obtained. The solar cell performance in this work is limited by the porosity of the absorber and the back contact quality. Despite a significant improvement during the course of this work, the remaining porosity of the absorber causes selenium to diffuse towards the back forming a thick MoSe2 layer and causing a high series resistance in the device. A low cost, solution-based technique was also developed for the deposition of aluminium-doped zinc oxide films that can be used as the transparent conductive oxide layer in thin film solar cells. This methodology involves the use of an ultrasonic spray pyrolysis system, which is a very versatile and easily controlled deposition technique. Although the presence of oxygen makes the film closer to stoichiometric (fewer oxygen vacancies) good electronic and optical properties have been obtained by process optimisation. Films deposited with optimum conditions exhibited a sheet resistance of 23 Ω/sq, which can be further reduced by increasing the thickness with minimal transmittance losses. The simplicity, low toxicity and straightforward control make the proposed methodologies extremely potential for low cost and scalable deposition of thin film solar cells

Nanostructured Materials for Energy Storage and Conversion

The conversion and storage of renewable energy sources is key to the transition from a fossil-fuel-based economy to a low-carbon society. Many new game-changing materials have already impacted our lives and contributed to a reduction in carbon dioxide emissions, such as high-efficiency photovoltaic cells, blue light-emitting diodes, and cathodes for Li-ion batteries. However, new breakthroughs in materials science and technology are required to boost the clean energy transition. All success stories in materials science are built upon a tailored control of the interconnected processes that take place at the nanoscale, such as charge excitation, charge transport and recombination, ionic diffusion, intercalation, and the interfacial transfer of matter and charge. Nanostructured materials, thanks to their ultra-small building blocks and the high interface-to-volume ratio, offer a rich toolbox to scientists that aspire to improve the energy conversion efficiency or the power and energy density of a material. Furthermore, new phenomena arise in nanoparticles, such as surface plasmon resonance, superparamegntism, and exciton confinement. The ten articles published in this Special Issue showcase the different applications of nanomaterials in the field of energy storage and conversion, including electrodes for Li-ion batteries and beyond, photovoltaic materials, pyroelectric energy harvesting, and (photo)catalytic processes

Functional oxides for optoelectronics

Il riscaldamento globale è tra le problematiche più urgenti che dobbiamo affrontare. Diminuire il consumo energetico e incrementare l’energia prodotta da fonti rinnovabili piuttosto che dai combustibili fossili sono azioni fondamentali per affrontare il cambiamento climatico. Dato che l’illuminazione è responsabile del 20% del consumo totale di energia e che il fotovoltaico è tra le fonti di energia rinnovabile che è cresciuta di più negli ultimi decenni, l’optoelettronica riveste un ruolo centrale in questa sfida. Molti degli impressionanti miglioramenti raggiunti negli ultimi decenni in questo campo sono stati resi possibili dallo sviluppo e dall’ottimizzazione dei materiali impiegati. Film sottili e nanostrutture di ossidi sono stati studiati in questo lavoro come una possibile soluzione a problematiche nel settore dell’optoelettronica. In particolare, nanocristalli di CsPbBr3 sono di largo interesse come emettitori di luce, ma risultano poco stabili quando esposti a umidità, solventi polari, ecc. Di conseguenza, nanocristalli di CsPbBr3 sono stati incapsulati in un guscio di silica (CsPbBr3@SiO2) sfruttando una reazione tra l’anidride maleica e il legante oleilammina sulla superficie del CsPbBr3. In particolare, nanocristalli di Cs4PbBr6 vengono convertiti dall’anidride maleica in nanocristalli di CsPbBr3 e l’aggiunta di un precursore della silica permette l’incapsulamento. Ulteriori esperimenti hanno rivelato il ruolo cruciale dei nanocristalli di Cs4PbBr6 e dell’ambiente di reazione ottenuto dopo la loro conversione per garantire la formazione di CsPbBr3@SiO2. Questo lavoro apre la strada allo studio della reattività dei leganti superficiali per l’incapsulazione dei nanocristalli, ma anche per strade alternative per lo scambio o la rimozione dei liganti, una nuova chimica per nanomateriali più stabili. Gli ossidi funzionali sono stati investigati anche in forma di film sottili per applicazioni fotovoltaiche. In dettaglio, la commercializzazione di celle solari a base di materiali emergenti come Cu(In,Ga)Se2 e Sb2Se3 contengono un buffer layer a base di CdS, un composto altamente tossico che ostacola la loro commercializzazione. Zn(1-x)MgxO è stato identificato come un potenziale materiale alternativo per celle solari a base di Cu(In,Ga)Se2 mentre la titania per Sb2Se3. Film sottili di Zn(1-x)MgxO sono stati preparati mediante deposizione da bagno chimico su substrati di vetro. E’ stato studiato il ruolo dell’etanolammina e dell’acido citrico insieme al contenuto di Mg sulle proprietà del film con lo scopo di impiegare questi film come buffer layer in celle solari al Cu(In,Ga)Se2 anche mediate calcoli degli equilibri in soluzione per comprendere il meccanismo di formazione del film. Analogamente, film sottili di titania sono stati preparati mediante spin coating su ossido di stagno drogato fluoro. Un trattamento acido è stato investigato per controllare il drogaggio nel film sottile di titania al fine di ottimizzare le performance della cella solare. Alcuni calcoli termodinamici sono stati eseguiti per confrontare la stabilità di fasi a diverso contenuto di titanio e di ossigeno.Nowadays, global warming is among the most urgent challenges that we have to meet. Decrease the energy consumption and enhance the amount of energy produced trough renewable sources rather than fossil fuels are imperative actions to deal with climate change. Since lighting is responsible of about 20 % of the total energy consumption and since photovoltaics is among the renewable energy source that grew more in the last decades, optoelectronics is a central field in such a challenge. Many of the crucial improvements that have been reached in the last decades in this field were made possible thanks to the development and optimization of the materials involved. In this study, oxides were investigated at the nanoscale and in the form of thin films as valuable solutions to current issues in modern optoelectronics. In particular, CsPbBr3 nanocrystals are interesting materials for light emission applications, but they suffer from poor stability against moisture, polar solvents etc. As a consequence, the reaction between maleic anhydride and the oleylamine capping ligand was exploited to encapsulate CsPbBr3 nanocrystals in SiO2 shells (CsPbBr3@SiO2). Maleic anhydride converted the starting Cs4PbBr6 nanocrystals into CsPbBr3 ones, and the addition of silica precursor promoted the shell growth. Further experiments revealed the crucial role played by Cs4PbBr6 nanocrystals as a starting material and of the reaction environment in order to successfully grow CsPbBr3@SiO2. This study paves the way for the exploitation of the reactivity of surface capping ligands for the encapsulation of nanocrystals, and potentially also for ligand exchange or stripping, a new chemistry route for more stable nanomaterials. Functional oxides were also investigated in the form of thin films for solar cell applications. Cu(In,Ga)Se2 and Sb2Se3 are emerging photovoltaic technologies whose market availability is limited by the presence of a toxic CdS buffer layer. Zn(1-x)MgxO was identified as a potential alternative oxide for the deposition of buffer layers for Cu(In,Ga)Se2 solar cells, whereas titania was investigated for cells based on Sb2Se3. In view of their application as buffer layers in Cu(In,Ga)Se2 solar cells, Zn(1-x)MgxO thin films were grown trough chemical bath deposition onto soda lime glass, in order to optimize the extent of Mg incorporation and the morphology of the film, the role of the complexing agent citric acid together with the nominal Mg amount was investigated. Likewise, titania thin films were prepared trough spin coating onto fluorine-doped thin oxide substrates. Several attempts were devoted to control and measure the n-type doping of the titania layers trough an acidic treatment with the final goal of improving the solar cell performance. Lastly, thermodynamic calculations allowed a stability comparison among TixOy species

Defect Characterization of Cu2ZnSnSe4 Thin Film Solar Cells Using Advanced Microscopic Techniques

Thin film chalcogenide solar cells have been utilized in a broad range of application for their tunable direct bandgap and high efficiency. In this work, we performeda novel fabrication and multiple high-resolution characterizations of Cu2ZnSnSe4(CZTSe) solar cells, which is believed to be a better candidate compared to well-developed CuInxGa(1-x)Se2(CIGS)for its earth-abundant contents. The fabrication is based on nanoparticle precursor production by liquid-phase pulsed laser ablation, electrophoretic deposition of precursor thin film under ambient condition, and selenization. Such non-vacuum fabrication has the advantage of low cost and minimum impact on the environment. By studying the CZTSe and CIGS fabricated in the above methods using techniques including Raman integrated scanning probe microscope, electron holography, scanning transmission electron microscopy and in-situ transmission electron microscopy. We discoveredthe origin of the performance limit of the CZTSe compared to CIGS as well as the defect of our non-vacuum fabrication methods. The presented results, including the characterization methods, create a novel way to correlate the solar cell performance with the microstructure in a nanometer scale. It opens up the possibility for developing high performance solar cell devices from the prospective of nanostructure and defect engineering.PHDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/140886/1/mjxu_1.pd