Additives Engineering for High-Performance All-Inorganic Cs Based Perovskite Solar Cells

The emerging perovskite solar cells (PSCs) have made a breakthrough in the photovoltaic community. To date, the power conversion efficiencies (PCEs) of the single junction PSCs have been increasing from 3.8% in 2009 to the latest record of 25.7%. Despite the impressive PCEs of PSCs, the material instability and short device lifetime are the major obstacles of future commercialization. For conventional organic-inorganic hybrid PSCs, the presence of methylamine ions (MA⁺), formamidine ions (FA⁺) and other organic components causes poor thermal stability of the perovskite thin films due to the volatile nature of the organic components at 80 – 100 °C. The preparation of all-inorganic perovskites such as CsPbX₃ (X = I, Br) can prevent the use of the volatile organic components, which is believed to be the potential solution for enhancing the thermal stability of perovskite thin films. However, the photovoltaic performance of all-inorganic Cs based PSCs is still below the conventional type of organic-inorganic hybrid PSCs. The quality of the all-inorganic perovskite film is one of the important factors in determining the device efficiency and stability. In this work, the ionic liquids (ILs) are used as the additives during the preparation of CsPbI₂Br. It is found that the crystallization of CsPbI₂Br and its surface morphology are significantly enhanced by using the controlled amount of ILs. A systematical investigation has been performed on the materials and devices. The experimental results show that incorporation of ILs is an effective method to fabricate high-performance CsPbI₂Br based solar cells.