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PhD : selection by topics

Technological challenges >> Solar energy for energy transition
7 proposition(s).

Integration in tandem devices of passivated contacts PV cells : Towards a multifunctional and universal interface technology

Département des Technologies Solaires (LITEN)

Laboratoire HoMoJonction

01-10-2020

SL-DRT-20-0758

thibaut.desrues@cea.fr

Solar energy for energy transition (.pdf)

This project aims to develop cristalline (c-Si) silicon PV cell technolologies with passivated contacts for tandem devices applications. To overcome conventional single junction cells limitations, one interesting research topic is about tandem structures which allow conversion efficiencies above 30%. For these tandem devices, it is necessary to optimise c-Si bottom cells fabrication processes to enhance the complementarity between both devices (Top and Bottom cells). The main goal of the PhD is to obtain universal c-Si Bottom cells adapted for all top cells technologies (Perovskite, CGS, III/V,...). These c-Si bottom cells will rely on the poly-Si/SiOx technology which allow to avoid the use of transparent conductive oxide (TCO)layers and also to obtain a great temperature stability of the devices. This last feature enables high temperature steps for the topcell fabrication processes. This project will consist in: 1/ Develop thin films and stacks optimized for bottom c-Si cells used in tandem architecture 2/ Characterize electrical and optical properties of the developed structures 3/ Integrate these structures into a tandem device using potentially different topcell technologies

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Elaboration and characterization of silicon / perovskite tandem solar cells with PIN architecture

Département des Technologies Solaires (LITEN)

Laboratoire Modules Photovoltaïques Organiques

01-09-2020

SL-DRT-20-0823

muriel.matheron@cea.fr

Solar energy for energy transition (.pdf)

Silicon / perovskite solar cells have recently shown major breakthoughs with record efficiencies reaching 28% for 2 terminal tandems (in which both subcells are connected in series). According to literature, best efficiencies are obtained with PIN architecture, due to optimized light management : minimized parasitic absorption from P layer in top cell, possibility to use transparent microcrystalline silicon as tunnel junction, or nanocrystalline silicon oxide with a better index matching property, leading to less parasitic reflection. Such materials (microcrystalline silicon and nanocrystalline silicon oxide) are developed within the frame of a PhD thesis at CEA-Liten, along with optimization of the perovskite single junction PIN architecture performed at CEA-Liten. The aim of the proposed PhD is to combine such developments into PIN tandems. Efforts will be devoted to in-depth characterization of the tunnel / recombination junctions and of the whole device. The goal is to identify charge transport mechanisms occurring at the interconnection layer between both subcells and to detect device limitations. To do so, electrical characterization of tests structures will be conducted, along with variable illumination measurements and photo/electroluminescence imaging of tandems. After a first analysis of PIN structures, new interconnection systems (obtained by chemical modification of interconnection materials) could be proposed and analyzed the same way.

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New High Efficiency DC / DC Converter Technology with Integrated Galvanic Isolation for Medium Voltage DC grids

Département des Technologies Solaires (LITEN)

Laboratoire Systèmes PV

01-06-2020

SL-DRT-20-0833

Stephane.CATELLANI@cea.fr

Solar energy for energy transition (.pdf)

The primary sources of electrical energy used in renewable energy systems are DC. We can indicate below, the main characteristics in tension of the sources in question: -Photovoltaic (1.5 kVDC) -Systems of energy storage (800 V-1.5 kVDC) -Stacks EHT (950 VDC) -Electric Vehicle Batteries (800 VDC) On the other hand, the new power transmission networks are in direct current: -HVDC: 100 kVDC to 1.6 MVDC Some rail power systems are also DC: -Rain: 1.5kVDC, 3kVDC, experimental network project SNCF 10kVDC Architectures with DC collector are planned in the following applications: -Distribution of energy in charging stations for electric vehicles -Nautical ship propulsion systems -Electrical conversion lines of railway traction units -Photovoltaic power generation Stationary storage of electrical energy The objective of this thesis work will be to obtain a modular DC / DC converter brick compatible with the voltage levels delivered by the ENR sources and allowing to inject on the DC medium voltage. Electrical isolation of primary sources will remain unchanged: therefore, to ensure the isolation of sources, very high efficiency transformer technologies (> 99.5%), integrated in the static conversion stages -Injection can be done on a DC 9kV network (experimental network SNCF) -The power electronics will be made with HT SiC semiconductors whose current performance is much higher than Si equivalents. The DTNM will bring its expertise on magnetic materials for the design of the integrated transformer in the conversion stages.

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Dynamic simulation and control of Continious solar fuel gazeification process

Département Thermique Biomasse et Hydrogène (LITEN)

Laboratoire des Systèmes Solaires et Thermodynamiques

01-10-2020

SL-DRT-20-0989

nathalie.dupassieux@cea.fr

Solar energy for energy transition (.pdf)

The topic of this thesis studies deals with the valorisation of solar energy as a storable and/or transportable energy vector. For this purpose, the so-called solar thermochemical processes, combining thermal solar technologies and thermochemical conversions of renewable or waste carbonaceous materials have been selected. The reactor studied previously implements endothermic reactions. Those reactions carry out under solar thermal input, generate gaseous products in which solar energy is stored in chemical form. For the scale-up of the SOLAR-FUEL reactors studied in previous work (theses, Carnot and European projects), a major obstacle to industrial deployment remains : the variability of the solar resource does not allow continuous operation. The objective of the research project is to propose a hybrid process (carbon/solar resource) able of continuously produce a renewable solar fuel. The research work will be based both on dynamic simulation and on experimental validation, in order to ensure optimal control of the process according to the available solar resource. The energy and environmental balance will also be studied in order to compare this solar energy storage pathway with other technologies.

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Modelling, Characterization and optimizations of electronic transport at the passivating contact PV cells interfaces

Département des Technologies Solaires (LITEN)

Laboratoire HETerojonction

01-10-2020

SL-DRT-20-1015

wilfried.favre@cea.fr

Solar energy for energy transition (.pdf)

Resistive losses reduction and engineering in PV cells are becoming a major topic for further efficiency increase. The main actors are focused to identify and quantify the different sources of losses at the various interfaces of the passivating contact PV devices. For this purpose there is a need to consider both test structures representative of the final PV cell (similar process) and operando conditions (light and temperature close to outdoor environment), while present methodologies are far away from these requirements (different fabrication process and dark conditions). The work will be divided into two main parts: (i) Participate to the development and validation of a new setup dedicated to characterization of PV cells contact resistance in operando conditions and (ii) evaluate physical models for the interfacial electronic transport using 2D/3D simulation tools together with advanced characterization techniques (EBIC, EPR). The samples will be produced in the CEA PV cells pilot lines at INES campus (24.63% record efficiency demonstrated) and the knowledge produced will allow further single junction and tandem device optmizations.

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Interaction mechanisms of hydrogen with defects of silicon bulk and at the interfaces of passivated contacts in PV cells

Département des Technologies Solaires (LITEN)

Laboratoire HoMoJonction

01-10-2020

SL-DRT-20-1018

raphael.cabal@cea.fr

Solar energy for energy transition (.pdf)

Although fluctuating, the photovoltaic market is still dominated by silicon technologies occupying ~94%. The most promising homo-junction cell architectures systematically integrate a so-called "passivated" contact through a stack of polycrystalline silicon on tunnel oxide. The hydrogenation of such structures makes it possible to achieve very efficient yields >25%. However, the introduction of hydrogen can also lead to layer delamination or resistive losses through accumulation effects at the interfaces, significantly degrading the efficiency of the final device. To avoid its effects and develop this type of structure with associated yields, it is essential to understand the interactions of hydrogen involved and to understand its role in passivation phenomena. However, hydrogen is an extremely difficult element to characterize by its very nature. Its characterization therefore represents a real challenge, to which are added the difficulties related to the textured surface state of solar silicon and the configuration of poly-Si/Si/SiOx/Si interfaces. To meet this challenge, the work proposed here will be to implement and correlate characterization techniques, allowing both to locate and quantify hydrogen in the volume of silicon and at the interfaces of passivated contact structures. The implementation of a characterization methodology will lead to the main objective of the thesis, which is to propose mechanisms of hydrogen interaction with defects and its role in the quality of passivated contacts. This will open up opportunities for the development and optimization of passivated contact structures. This study will benefit from the infrastructure for the realization of samples from CEA-LITEN in INES and the means of characterization of the nano-characterization platform with its expert environment.

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Improvement and understanding of the performance of silicon cell-based solar generators in harsh environments

Département des Technologies Solaires (LITEN)

Laboratoire Photovoltaïque à Concentration

01-09-2020

SL-DRT-20-1061

philippe.voarino@cea.fr

Solar energy for energy transition (.pdf)

The thesis will be carried out at the interface of several laboratories of the Department of Solar Technologies (DTS) of the CEA located in Le Bourget du Lac on the campus of the National Institute for Solar Energy (INES). The objective of this thesis is to improve the resistance to environmental conditions (radiation, e/H+, UV, thermal cycling) of space solar generators based on silicon solar cells, and to better understand the degradation mechanisms of cells/materials associated. By finely controlling the manufacturing of cells (doping, impurity, architecture, etc.) and modules (materials, thickness, architecture, optical trapping, etc.), it is possible to improve the performance of silicon modules at the end of their lifetime while maintaining a competitive price (?/W), 1 to 3 orders of magnitude lower than space III-V modules.

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