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.

High Efficiency Perovskite‐Silicon Tandem Solar Cells: Effect of Surface Coating versus Bulk Incorporation of 2D Perovskite

“…Therefore, we were able to reduce the thickness of the Spiro‐MeOTAD layer to around 110 nm to reduce its parasitic absorption in the long wavelength region without affecting the cell reproducibility, which previously had been negatively affected . We also thinned down the MoO 3 thickness from 10 to 5 nm to reduce the parasitic absorption of the layer as this layer becomes absorbing after the transparent conduction oxide sputtering process as shown in a previous report . We used the surface coating–low concentration with n ‐BABr to fabricate semitransparent perovskite cells.…”

Transparent Electrodes for Efficient Optoelectronics

“…[111,130] As mentioned earlier, gentle deposition on underlying layers can also be a critical factor in electrode choice and raises questions about the use of well-established physical vapor deposition (PVD) techniques, such as sputtering or pulsed laser deposition for certain applications. Sputter damage, caused by UV radiation and particle bombardment, is a known phenomenon in organic, [16] SHJ, [15] and perovskite [169] solar cells as well as flexible displays. Solutions to overcome such damage include the use of remote plasma sources, [170] the use of gently deposited buffer layers [171] or further improvements to solution-based deposition processes to improve the density and purity of TCO films to achieve high electron mobilities at low temperatures.…”

Two‐Terminal Perovskites Tandem Solar Cells: Recent Advances and Perspectives

“…Therefore, the requirement of three transparent electrodes poses a grand challenge for four‐terminal tandems. Due to free‐carrier absorption, significantly increased parasitic absorption losses occur over the wavelength range of 850–1200 nm in the transparent electrodes, especially for layers beyond 100 nm thick. There are several well‐identified routes to minimize a parasitic loss, and one strategy is reducing the layer thickness of transparent electrodes .…”