engleski

Optimization of transparent thin film TiO2 nanotube arrays for perovskite solar cells

From humble beginnings as an industry grade pigment, TiO2 as a semiconducting metal oxide has been thoroughly researched. Advanced applications in water treatment (photocatalysis), water splitting, sensors, self-cleaning surfaces, UV- blockers in sunscreens, batteries show the shear versatility and the popularity of this compound. Due to its non-toxicity, good mechanical and chemical stability, opto-electric properties it has also found its way into third generation solar cells, i.e. TiO2 is used as an electron transport layer in dye-sensitized solar cells (DSSC), organic solar cells (OSC) and perovskite solar cells (PSC). PSC are a promising new photovoltaic technology that offers different chemical or physical synthesis routes with the only drawback being the need of fabrication in inert atmospheres like gloveboxes filled with Ar or N2 due to their sensitivity to oxygen and humidity. However, their highest selling point is their leap in efficiencies from 3.8% in 2009 to 25, 2% in 2022 [1], and the low quantity of material needed for fabrication. Most common PSC are comprised as follows: substrate (conductive metal oxide glass, e.g. FTO or ITO), electron transport layer (ETL), perovskite active layer (active layer), hole transport layer (HTL) and finally an evaporated thin film metal contact (Au, Ag). When photons pass through the PSC, the ones with sufficient energies excite the active perovskite layer and electron-hole pairs are generated. These photogenerated species have to be separated, transported and collected by the electrodes (conductive oxides on glass and evaporated contacts) on both sides for the cell to produce electricity. This is separation and transport of charges is done by the aforementioned ETLs and HTLs due to their intrinsic electric fields and interface interactions with the active layer. A huge point of interest in PSC technology is the use of nanostructured ETLs as a potential way to increase the contact surface between the layers, to mitigate lower electron diffusion lengths (than the ones of holes) in perovskites, thus improving the separation of charges and finally increasing the conversion efficiency of PSC. TiO2 nanotubes are a 1D nanostructure that is especially interesting due to their high aspect ratio, porosity, elongated morphology and thin walls that facilitate electron transport down their tubular shape [2]. In this work, we present the optimization process of transparent thin film TiO2 nanotubes (TNTs) for the use as an ETL for PSC. They were prepared by anodizing Ti thin films deposited by magnetron sputtering. Different film thicknesses, anodization parameters, pore-widening techniques, perovskite concentrations, were implemented which were later correlated with opto-electric properties (for TNTs), J-V curves and external quantum efficiencies (for solar cells). Also scanning electron microscopy was used to track any potential changes in morphology during the TNT optimization. Regarding our optimization process in this work, we managed to optimize our system from a modest starting efficiency of 5% to up to 14% efficiency which is among the top efficiencies regarding perovskite solar cells containing thin film TNT ETLs published in current literature [3]. [1] https://www.nrel.gov/pv/cell-efficiency.html [2] U. Thakur, R. Kisslinger, K. Shankar, One- dimensional electron transport layers for perovskite solar cells, Nanomaterials 7 (2017) (5) 95. [3] P. Qin, M. Paulose, M.I. Dar, T. Moehl, N. Arora, P. Gao, O. K. Varghese, M. Grätzel, M. K. Nazeeruddin, Stable and efficient perovskite solar cells based on titania nanotube arrays. Small 11 (2015) (41) 5533–5539.

TiO2 nanotubes, perovskite solar cells

nije evidentirano