Learning by Research

Thesis Title: Atmospheric-Pressure Spatial Atomic Layer Deposition of Cu2O and Functional Thin Films for Photovoltaic Applications

Copper-based thin films are a hot topic in the material science community due to the abundance of copper, its non-toxicity, and the many different applications that they can find. Nowadays the different Cu phases are used for diversified applications such as photovoltaic, antimicrobial, photocatalysis, and several optoelectronic applications. In particular, copper (I) oxide (or cuprous oxide, Cu2O) represents one of the oldest studied p-type semiconductor materials (1927) since all the theories of physics were first based on it. The lack of efficient semitransparent p-type materials require more effort and understanding towards their fundamental properties and thus allowing a better integration into devices at the research and industrial scale. In this thesis, we have focused first on the development and study of cuprous oxide thin films with an innovative and scalable approach known as atmospheric pressure spatial atomic layer deposition (AP-SALD), which allows deposition at low temperatures, high-throughput, and open-air atmosphere. We have investigated the different properties of the Cu2O films deposited with a thermally stable precursor known as Cu(hfac)(COD) that has never been used to deposition Cu2O by ALD and/or CVD method. The obtained results have demonstrated a crystalline, pure phase, high mobility, and quality cuprous oxide thin film. Besides, the transport properties were correlated with the formed defects at the surface and bulk level based on Raman measurements. The obtained results have been compared with films deposited with another precursor Cu(hfac)(TMVS) that has been already optimized for the deposition of Cu2O by AP-SALD. As the second part of this work, we have studied the effect of oxygen doping within the metal oxide film and found out a record resistivity value obtained with respect to other growth techniques since 1990. The formation of the defects have been quantified to assess the impact of the oxygen doping, thanks to an advanced characterization technique known as positron annihilation lifetime spectroscopy (PALS) performed in at the mono-energetic positron spectroscopy (MePS) beamline at HZDR (Germany) along with DFT calculations. This study has shed light on the mechanism of defect formation in Cu2O in general and in our thin films in particular. The integration of the metal oxide to semi-transparent solar cell devices integrated into buildings for outdoor and indoor application as an absorber has been studied since the optimized films were combined with ZnO thin films also grown by SALD. The obtained results have been allied with an in-depth simulation study based on the SCAPS software. Flexible tests have been carried out to study the resistance of the thin films but also devices to harsh conditions since they can be integrated into different shapes as solar harvesters in building for instance as glazing or smart windows. Similarly, the Cu2O thin film has been integrated as a hole transport layer (HTLs) in a large area of silicon heterojunction solar cells (SHJ) within the framework of a collaboration with CEA at The National Institute of Solar Energy in France. Finally, this study reports the ability to control the three main phases of Cu-based films from metallic to oxidized phases by altering only the co-reactant. Thus, the mechanism of growth is explained through disproportionation and hydrolysis reactions. The originality of this last part remains in the deposition of the three phases using an open-air spatial atomic layer deposition (AP-SALD) and low-temperature processing.

Key Words: Atomic Layer, Photovoltaics, Functional

Doctoral School: ED I-MEP² - Ingénierie - Matériaux, Mécanique, Environnement, Énergétique, Procédés, Production
Research Laboratory:  Laboratoire des Matériaux et du Génie Physique (LMGP, CNRS/Grenoble INP-UGA)
Thesis Supervision:  David MUNOZ-ROJAS, Anne KAMINSKI-CACHOPO and Guy CHICHIGNOUD

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