Crecimiento y caracterización de monocristales en volumen de CdTe dopados con Bi

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura 26-03-2007Bibliografí

Over 10% efficient wide bandgap CIGSe solar cells on transparent substrate with Na predeposition treatment

With the recent rise of new photovoltaic applications, it has become necessary to develop specific optoelectronic properties for thin-film technologies such as Cu(In,Ga)Se2 and to take advantage of their high degree of tunability. The feasibility of efficient wide bandgap absorbers on transparent conductive oxide substrates is, in that context, of critical importance. Using an original approach based on a predeposition sodium treatment, Cu(In,Ga)Se2 absorbers fabricated by sputtering and reactive annealing with a Ga to (Ga + In) content over 0.7 and an optical bandgap above 1.4 eV are deposited on transparent fluorine-doped tin oxide films, with the insertion of an ultrathin MoSe2 layer preserving the contact's ohmicity. Different material characterizations are carried out, and a thorough Raman analysis of the absorber reveals that the sodium pretreatment significantly enhances the Ga incorporation into the chalcopyrite matrix, along with markedly improving the film's morphology and crystalline quality. This translates to a spectacular boost of the photovoltaic performance for the resulting solar cell as compared with a reference device without Na, specifically in the voltage and fill factor. Eventually, an efficiency exceeding 10% is obtained without antireflection coating, a record value bridging the gap with the state of the art on nontransparent substrates.Peer ReviewedPostprint (author's final draft

Progress and perspectives of thin film kesterite photovoltaic technology: a critical review

The latest progress and future perspectives of thin film photovoltaic kesterite technology are reviewed herein. Kesterite is currently the most promising emerging fully inorganic thin film photovoltaic technology based on critical raw-material-free and sustainable solutions. The positioning of kesterites in the frame of the emerging inorganic solar cells is first addressed, and the recent history of this family of materials briefly described. A review of the fast progress achieved earlier this decade is presented, toward the relative slowdown in the recent years partly explained by the large open-circuit voltage (VOC) deficit recurrently observed even in the best solar cell devices in the literature. Then, through a comparison with the close cousin Cu(In,Ga)Se2 technology, doping and alloying strategies are proposed as critical for enhancing the conversion efficiency of kesterite. In the second section herein, intrinsic and extrinsic doping, as well as alloying strategies are reviewed, presenting the most relevant and recent results, and proposing possible pathways for future implementation. In the last section, a review on technological applications of kesterite is presented, going beyond conventional photovoltaic devices, and demonstrating their suitability as potential candidates in advanced tandem concepts, photocatalysis, thermoelectric, gas sensing, etc.Peer ReviewedPostprint (published version

Life cycle assessment of different chalcogenide thin-film solar cells

Thin-film photovoltaics (PV) cells offer several benefits over conventional first-generation PV technologies, including lighter weight, flexibility, and lower power generation cost. Among the competing thin-film technologies, chalcogenide solar cells offer promising performance on efficiency and technological maturity level. However, in order to appraise the performance of the technology thoroughly, issues such as raw materials scarcity, toxicity, and environmental impacts need to be investigated in detail. This paper therefore, for the first time, presents a cradle to gate life cycle assessment for four different emerging chalcogenide PV cells, and compares their results with copper zinc tin sulfide (CZTS) and the commercially available CIGS to examine their effectiveness in reducing the environmental impacts associated with PV technologies. To allow for a full range of indicators, life cycle assessment methods CML 2001, IMPACT 2002+, and ILCD 2011 were used to analyse the results. The results identify environmental hotspots associated with different materials and components and demonstrate that using current efficiencies, the environmental impact of copper indium gallium selenide (CIGS) for generating 1kWh electricity was lower than that of the other studied cells. However, at comparable efficiencies the antimony-based cells offered the lowest environmental impacts in all impact categories. The effect of materials used was also found to be lower than the impact of electricity consumed throughout the manufacturing process, with the absorber layer contributing the most to the majority of the impact categories examined. In terms of chemicals consumed, cadmium acetate contributed significantly to the majority of the environmental impacts. Stainless steel in the substrate/insulating layer and molybdenum in the back contact both contributed considerably to the toxicity and ozone depletion impact categories. This paper demonstrates considerable environmental benefits associated with non-toxic chalcogenide PV cells suggesting that the current environmental concerns can be addressed effectively using alternative materials and manufacturing techniques if current efficiencies are improved.Peer ReviewedPostprint (published version

Influence of compositionally induced defects on the vibrational properties of device grade Cu2ZnSnSe4 absorbers for kesterite based solar cells

This work presents a detailed analysis of the impact of compositionally induced defects on the vibrational properties of Cu2ZnSnSe4 absorbers for kesterite based solar cells. Systematic changes in the intensity of the E and B modes located around the 170, 220, and 250 cm 1 frequency regions, which involve mostly cation vibrations, were observed and analyzed in relation to the occurrence of different kinds of defect clusters involving VCu, ZnCu, ZnSn, CuZn, and SnZn point defects. Additional changes are also interpreted in terms of the appearance of SnSe, ZnSe, and CuSe-like contributions at the 185 and 250 cm 1 spectral regions, respectively. The sensitivity of the Raman measurements to the presence of these kinds of defects corroborates the potential of Raman scattering for point defect assessment in these systems

Numerical investigation of interface passivation strategies for Sb2Se3/CdS solar cells

Sb2Se3 is an emerging earth-abundant material praised for its promising optoelectronic properties, although the presence of interfacial defects at the vicinity of the p–n junction limit its performance as photovoltaic absorber. Using a device modeling approach and a realistic set of material parameters, it unravels pathways mitigating the impact of interfacial defects with a baseline Sb2Se3/CdS. Two straightforward strategies are devised and tested against the baseline. First, a thin front surface sulfurization of the Sb2Se3 absorber allowing a local lowering of the valence band and creating a “front surface field,” resulting in an increased carrier selectivity and limiting the density of holes available for interface recombination, leading to a significant efficiency improvement for optimized conditions. Second, the use of an ultrathin insulating Al2O3 layer between the absorber and the buffer layer is considered, helping in preventing detrimental chemical interdiffusion at the junction. This strategy provides a direct interface passivation, though the interlayer thickness needs a fine tuning to balance the benefits of reduced interface recombination and a detrimental Al2O3 low-conductivity layer. In each case, an analysis covering a broad range of parameters is presented, and conclusions are made in the frame of past numerical and experimental results.The authors thank Prof. Marc Burgelman, for his invaluable contribution to the field of photovoltaics by designing the program SCAPS, now widely used by various research groups around the world. The authors acknowledge the European Research Council ERC-CoG grant SENSATE (grant agreement ID: 866018) for the financial support of this work. This work is part of the R+D+i MaterOne project ref. PID 2020-116719RB-C41 funded by MCIN/AEI/10.13039/5011000110033. M.P. acknowledges the Spanish Ministry of Science and Innovation (MCIN) for the financial support in the frame of the Ramon y Cajal program (RYC-2017-23758).Peer ReviewedPostprint (author's final draft

Small atom doping: a synergistic strategy to reduce SnZn recombination center concentration in Cu2ZnSnSe4

Kesterite Cu2ZnSnS x Se4-x (CZTSSe) is among the most promising inorganic Earth-abundant thin-film photovoltaic technologies, although currently, the larger voltage deficit compared with more mature chalcogenide technologies is hampering solar-to-electricity conversion efficiency progress in these materials. Most of the latest reports agree on the CZTSSe defect structure as the main limitation for the open-circuit voltage. Small atom doping is suggested as an interesting strategy to reduce the concentration of defects without affecting secondary phase formation. Herein, an innovative approach based on the introduction of LiAlH4 and its further decomposition during the selenization process of CZTSe precursors, as a pathway for hydrogen and lithium/alkali transient doping, is explored. This process shows a strong beneficial influence on the crystal growth and solar cell device performance, especially with a significant improvement in V oc and fill factor. A reduction of nonradiative recombination and a remarkable fourfold increase in the carrier lifetime correlating with the reduction of the open-circuit voltage (V oc) deficit below 330¿mV is demonstrated. A mechanism on how small atoms (Li and H) interact to reduce the concentration of SnZn recombination centers while keeping doping relatively unchanged is proposed, opening fundamental perspectives for the simple and universal transient doping of thin-film chalcogenide compounds.Peer ReviewedPostprint (published version

Progress and perspectives of thin film kesterite photovoltaic technology: a critical review

The latest progress and future perspectives of thin film photovoltaic kesterite technology are reviewed herein. Kesterite is currently the most promising emerging fully inorganic thin film photovoltaic technology based on critical raw-material-free and sustainable solutions. The positioning of kesterites in the frame of the emerging inorganic solar cells is first addressed, and the recent history of this family of materials briefly described. A review of the fast progress achieved earlier this decade is presented, toward the relative slowdown in the recent years partly explained by the large open circuit voltage (VOC) deficit recurrently observed even in the best solar cell devices in the literature. Then, through a comparison with the close cousin Cu(In,Ga)Se2 technology, doping and alloying strategies are proposed as critical for enhancing the conversion efficiency of kesterite. In the second section herein, intrinsic and extrinsic doping, as well as alloying strategies are reviewed, presenting the most relevant and recent results, and proposing possible pathways for future implementation. In the last section, a review on technological applications of kesterite is presented, going beyond conven tional photovoltaic devices, and demonstrating their suitability as potential candidates in advanced tandem concepts, photocatalysis, thermoelectric, gas sensing, etc

Effect of post annealing thermal heating on Cu2ZnSnS4 solar cells processed by sputtering technique

In this work, a detailed study of the effect of thermal treatment (hot plate) on a Mo/CZTS/CdS/i-ZnO/ITO solar cell was carried out, which promotes the diffusion of the Cd contained in the window layer of CdS towards the absorber layer of CZTS. The thermal treatment of the Mo/CZTS/CdS/i-ZnO/ITO solar cell was carried out at temperatures ranging from 100 °C to 400 °C and times varying from 3 to 15 min in air atmosphere. The CZTS was grown from deposits of metallic precursors (Cu/Sn/Cu/Zn) by sputtering and annealing at two ramps: 200° C for 45 min with an argon flow of 1 mbar and 550 °C for 5 min at 1 bar in an atmosphere of S + Sn. For the complete solar cells with a hotplate treatment of 280 °C for 6 min an increase of 2.7% to 5.2% of conversion efficiency was observed compared to the solar cell without hotplate treatment. The band gap CZTS decreased from 1.56 to 1.43 eV and Jsc increased from 12.0 mA/cm2 to 15.4 mA/cm2.Peer ReviewedPostprint (author's final draft

Towards low cost and sustainable thin film thermoelectric devices based on quaternary chalcogenides

This is the peer reviewed version of the following article: Isotta, E. [et al.]. Towards low cost and sustainable thin film thermoelectric devices based on quaternary chalcogenides. "ADVANCED FUNCTIONAL MATERIALS", 20 Maig 2022, núm. 2202157, which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/adfm.202202157. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.A major challenge in thermoelectrics (TEs) is developing devices made of sustainable, abundant, and non-toxic materials. Furthermore, the technological drive toward low sizes makes crucial the study of nano and micro configurations. In this work, thin film TE devices based on p-type Cu2+xZn1-xSnS4 and Cu2+xZn1-xSnSe4, and n-type AlyZn1-yO are fabricated by physical vapor deposition. The kesterite phases show good purity and promising TE power factor, likely enhanced by the copper–zinc order–disorder transition. Thin film generators in planar configuration are assembled by a sequential deposition of the p-type, n-type, and contact materials. The power per unit planar area reaches 153 and 279 nW cm-2 for the sulphur- and selenium-based generators, respectively. These values significantly outperform any other literature attempt based on sustainable and low-cost thin films. Furthermore, if compared with traditional TEs often made of scarce and toxic materials, these devices offer a cost reduction above 80%. This allows reaching comparable values of power density per unit material cost, representing a first real step toward the development of sustainable and non-toxic thin film TE devices. These can find applications in micro energy harvesters, microelectronics coolers, and temperature controllers for wearables, medical appliances, and sensors for the internet of things.A.J. thanks the European Social Fund+ for the FI fellowship. The authors would like to acknowledge the help of Dr. Mirco D’Incau, Dr. Narges Ataollahi, and Prof. Della Volpe for the design of the measuring setup, as well as useful discussion with Prof. Dario Narducci. This research has received funding from the Spanish Ministry of Science, Innovation and Universities under the MATER-ONE projects (PID2020-116719RB-C41). Authors from IREC belong to the SEMS (Solar Energy Materials and Systems) Consolidated Research Group of the “Generalitat de Catalunya” (ref. 2017 SGR 862) and are grateful to European Regional Development Funds (ERDF, FEDER Programa Competitivitat de Catalunya 2007–2013). M.G. acknowledges the financial support from Spanish Ministry of Science, Innovation and Universities within the Juan de la Cierva fellowship (IJC2018-038199-I). E.S. acknowledges the ICREA Academia Program. Open Access Funding provided by Universita degli Studi di Trento within the CRUI-CARE Agreement.Peer ReviewedPostprint (published version