Influence of the surface treatment of PEDOT:PSS layer with high boiling point solvent on the performance of inverted planar perovskite solar cells

Since perovskite precursor solution is typically prepared from high boiling point solvents, understanding the effect of high boiling point solvent treatment of the PEDOT:PSS layer on the performance of perovskite solar cells is important for device processing optimization. In this paper, influence of the surface treatment of the PEDOT:PSS layer with high boiling point solvent, including N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and ethylene glycol (EG), on the device performance of the perovskite solar cells was investigated. Increased conductivity was measured for the PEDOT:PSS film after solvent treatments, which was ascribed to the partial removal of PSS component from the PEDOT:PSS layer, as evidenced by the UV–vis absorption spectroscopy and XPS spectroscopy. In comparison with the reference cell, poorer device performance was obtained for the perovskite solar cells directly deposited on the solvent washed PEDOT:PSS film, which was ascribed to the increased pin hole density of the perovskite films. However, insertion of a thin PSSNa layer between the PEDOT:PSS layer and the perovskite layer greatly improved device performance, demonstrating that PSS-rich surface is favorite for the crystal growth of the perovskite film. Increased external quantum efficiency over 600–750 nm was measured for the cells based on solvent treated PEDOT:PSS layer, leading to a short circuit current and the consequent performance enhancement.