title: Parasitic Absorption Reduction in Metal Oxide-Based Transparent Electrodes: Application in Perovskite Solar Cells.
abstract: Transition metal oxides (TMOs) are commonly used in a wide spectrum of device applications, thanks to their interesting electronic, photochromic, and electrochromic properties. Their environmental sensitivity, exploited for gas and chemical sensors, is however undesirable for application in optoelectronic devices, where TMOs are used as charge injection or extraction layers. In this work, we first study the coloration of molybdenum and tungsten oxide layers, induced by thermal annealing, Ar plasma exposure, or transparent conducting oxide overlayer deposition, typically used in solar cell fabrication. We then propose a discoloration method based on an oxidizing CO2 plasma treatment, which allows for a complete bleaching of colored TMO films and prevents any subsequent recoloration during following cell processing steps. Then, we show that tungsten oxide is intrinsically more resilient to damage induced by Ar plasma exposure as compared to the commonly used molybdenum oxide. Finally, we show that parasitic absorption in TMO-based transparent electrodes, as used for semitransparent perovskite solar cells, silicon heterojunction solar cells, or perovskite/silicon tandem solar cells, can be drastically reduced by replacing molybdenum oxide with tungsten oxide and by applying a CO2 plasma pretreatment prior to the transparent conductive oxide overlayer deposition.
authors.affiliation: Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL) , Rue de la Maladière 71b, 2002 Neuchâtel, Switzerland.
authors.forename: Jérémie
authors.initials: J
authors.lastname: Werner
authors.affiliation: Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL) , Rue de la Maladière 71b, 2002 Neuchâtel, Switzerland.|CSEM, PV-Center, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland.
authors.forename: Jonas
authors.initials: J
authors.lastname: Geissbühler
authors.affiliation: Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL) , Rue de la Maladière 71b, 2002 Neuchâtel, Switzerland.
authors.forename: Ali
authors.initials: A
authors.lastname: Dabirian
authors.affiliation: CSEM, PV-Center, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Nicolay
authors.affiliation: Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL) , Rue de la Maladière 71b, 2002 Neuchâtel, Switzerland.
authors.forename: Monica
authors.initials: M
authors.lastname: Morales-Masis
authors.affiliation: Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL) , Rue de la Maladière 71b, 2002 Neuchâtel, Switzerland.
authors.forename: Stefaan De
authors.initials: SD
authors.lastname: Wolf
authors.affiliation: Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL) , Rue de la Maladière 71b, 2002 Neuchâtel, Switzerland.|CSEM, PV-Center, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland.
authors.forename: Bjoern
authors.initials: B
authors.lastname: Niesen
authors.affiliation: Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL) , Rue de la Maladière 71b, 2002 Neuchâtel, Switzerland.|CSEM, PV-Center, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland.
authors.forename: Christophe
authors.initials: C
authors.lastname: Ballif
keywords: CO2; molybdenum oxide; perovskite; plasma treatment; silicon heterojunction; solar cell; tandem; tungsten oxide