## 1 Introduction  
Due to the continued global energy demands, alternative energy sources that are sustainable and less harmful to the environment have been explored. Perovskite solar cells (PSCs) have attracted significant interest owing to their continued improvement in performance and efficiency, use of low cost materials, and simple manufacturing process. During the last decade, the efficiency of the organic-inorganic halide hybrid PSCs has improved from 4% in 2009 [1] to more than 25.6% in 2021 [2]. Since electron transport layer (ETL) plays a significant role in the performance of perovskite solar cells, doping of the ETL is one of the most common approaches and effective strategies used to improve the performance of the PSCs. The ETL has also a significant influence on the morphology, optical properties and consequently on the perovskite film quality. Different materials have been employed in the fabrication of the ETL [3]. However, titanium dioxide (TiO\({}_{2}\)) is still the dominant material used in the ETL because of its high transparency, good stability and low cost [4]. The undoped mesoporous TiO\({}_{2}\) (M-TiO\({}_{2}\)) possess in-between energy gap defects forming electron traps between the conduction and valence bands due to oxygen vacancy defects, hindering the charge transport extraction and increase in carrier recombination [5, 6]. Lithium and FK209 cobalt have been proposed to dope the M-TiO\({}_{2}\) because they improve materials properties using cheap chemicals and easy fabrication process. Many studies have demonstrated that doping TiO\({}_{2}\) with lithium and FK209 cobalt results in a decrease in the carrier recombination, electron traps density, defects and improved the conductivity of the ETL [7, 8, 9, 10, 11]. Different strategies have been adopted to improve the efficiency of the PSCs including increasing the conductivity and transparency of the ETL. In this study, different doping technique to enhance the electrons transfer properties of the M-TiO\({}_{2}\) was investigated. The dopant enables faster electrons transfer and extraction through the M-TiO\({}_{2}\) layer, which leads to improved efficiency of the PSCs. Tris(2-(1H-pyrazol-1-yl)-4-tert-utlypyridine) cobalt (III) tri[bis(trifluoromethane)sulfoni mide] FK209 Co(III) TFSI salt and Bis(trifluoromethane) sulfonimide lithium salt (TFSI) were investigated as dopant for the M-TiO\({}_{2}\) in the ETL. This is to improve the conductivity and mobility of the ETL and to reduce hysteresis effect. A mixture of lithium and cobalt were prepared and examined to study the influence of this compound on the perovskite carriers lifetime and on the overall device performance. One of the most common technology employed to enhance the electrons transfer properties of the M-TiO\({}_{2}\) is doping. Doping the ETL results in a decrease in the carrier recombination rate, reduction in the electron traps density, and improve the conductivity of the ETL which consequently decrease the series resistance of the PSC [12]. Numerous articles have been published on doping the ETL with various elements. For example, [PERSON] et al. investigated the effect of using lithium TFSI salt (Li\({}^{+}\)) as a dopant for the compact TiO\({}_{2}\). They showed that using Li\({}^{+}\) doped compact titanium dioxide (C-TiO\({}_{2}\)) could increase the TiO\({}_{2}\) mobility and reduce the density of electron traps, resulting in increasing the efficiency of PSCs to 17% [7]. In 2018, [PERSON] et al. reported on C-TiO\({}_{2}\) prepared using aerosol spray pyrolysis and studied the effect of using FK209 cobalt complex treatment of the M-TiO\({}_{2}\) for ETL [9]. The ETL in [PERSON]'s study consisted mainly of two layers. The first layer was a blocking TiO\({}_{2}\) and the second layer was M-TiO\({}_{2}\) treated with different concentrations of FK209. This method required two high temperature treatments, the first is performed by holding the sample at 500 \({}^{\circ}\)C for 1 h and the second by annealing the sample at 450 \({}^{\circ}\)C for 30 min.