Développement d'électrodes transparentes par méthodes de dépôt à pression atmosphérique et bas coût pour applications photovoltaïques / Development of transparent electrodes by vacuum-free and low-cost deposition methods for photovoltaic applications
The thesis work involves the study of Indium-free Transparent Conductive Materials (TCMs), which constitute key components of many optoelectronic devices, using Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD). This new approach shares the main advantages of conventional ALD but allows open-air, very fast deposition of high-quality nanometer-thick materials over large surfaces. We focused on the optimization of the electrical properties of Aluminum doped Zinc Oxide (ZnO:Al) films, one of the most studied Transparent Conductive Oxides (TCOs). The effect of several experimental parameters on the physical properties of the deposited films has been evaluated. The carrier transport mechanism limited by grain boundaries was identified to be tunneling rather than thermionic emission in highly doped ZnO, thanks to a new model we have developed using the Airy Function Transfer Matrix Method. Accordingly, the electron trap density at grain boundaries for ZnO:Al samples (carrier concentration of 2.2×1020 cm?3) prepared by AP-SALD was estimated to be about 7.6×1013 cm?2. Our model shows that grain boundary scattering is the dominant scattering mechanism in our films. We found that UV assisted annealing (~ 200 °C) under mild vacuum was an efficient method to reduce grain boundary traps, resulting in an improvement of mobility from 1 cm2V?1s?1 to 24 cm2V?1s?1 for ZnO and to 6 cm2V?1s?1 for ZnO:Al. We have also used AP-SALD to fabricate high-performance, stable and flexible TCMs based on metallic nanowire network. For that, we developed composite electrodes by coating silver/copper nanowires (AgNWs/CuNWs) with ZnO, Al2O3, or ZnO:Al. A thin conformal ZnO coating deposited by AP-SALD technique enhanced drastically the thermal/electrical stability of the AgNWs network. High optoelectronic properties (sheet resistance of about 7 ?/sq, transmittance of about 83 %) of the AgNW/ZnO:Al composite make them very appropriate for application as TCM, especially for flexible devices. Finally, as a soft deposition technique, AP-SALD is completely compatible to the silicon heterojunction (SHJ) solar cell technology in terms of interface passivation. The integration of ZnO:Al films to SHJ solar cell has been briefly explored.
Membres du Jury/Jury members
Dr - D. Lincot - Institut Photovoltaïque Ile de France (IPVF) (France) - Rapporteur
Prof.- C. Voz - Universitat Politècnica de Catalunya (Spain) - Rapporteur
Prof. - C. Vallée - LTM, CNRS, Grenoble (France) - Examiner
Dr- E. Blanquet - SIMaP – CNRS, Grenoble (France) - Examiner
Prof - . G. Kiriakidis - University of Crete (Greece) - Examiner
Dr - M. Maglione - Institut de Chimie de la Matière Condensée de Bordeaux (France) - Examiner
Dr.- D. Muñoz-Rojas - LMGP, CNRS, Grenoble INP Minatec, Grenoble (France) - Thesis Director
Prof.- D. Bellet - LMGP, CNRS, Grenoble INP Minatec, Grenoble (France) - Thesis Co-director
Dr. - D. Muñoz - CEA, LITEN, INES, Le Bourget-du-Lac (France) - Thesis Co-director