Methylammonium lead mixed-halide perovskite (CH 3 NH 3 -PbI 3¹x Cl x ) has been widely used for photovoltaic conversion. Supposedly, the presence of chloride ions in perovskite precursors enhances the coverage, morphology, and stability of the final perovskite film. It also improves carrier diffusion length in the perovskite film. Due to these advantages, the mixed-halide compound has been adopted for use in planar structure perovskite solar cells and it has led to significant enhancement in power conversion efficiency. However, until now, the exact content of chloride in the final product (CH 3 NH 3 PbI 3¹x Cl x ) is under debate and has not been reported yet. In this article, we show the exact amount of chloride ions in the final perovskite film, determined by chemical analysis with ion chromatography.Perovskite solar cells have become a very important topic of research in the last few years. The power conversion efficiency of cells using methylammonium lead iodide perovskite (CH 3 -NH 3 PbI 3 ) as a light-harvesting material for the first time in a liquid-state perovskite-sensitized solar cell was 3.8%.1 However, the fundamental problem in this liquid-state cell was easy dissolution of perovskite into the liquid electrolyte. After two years, the same group reported 0.37% power conversion efficiency for the first time in a solid-state perovskite solar cell using a carbonpolymer conductive composite as the hole transport material. 2 In the following years, use of spiroOMeTAD (2,2¤,7,7¤-tetrakis(N,N-dimethoxyphenylamine)-9,9¤-spirobifluorene) as the hole transport material (HTM) brought about a leap in cell performance and led to continuous and fast progress. 3,4 Recently, a efficiency of 20.1% has been reported.
5Lead iodide perovskite materials can be used either in a mesoscopic or a planar cell structure. 4,6,7 The principal perovskite layer in meso and planar architectures is usually composed of either pure iodide (CH 3 NH 3 PbI 3 ) or mixed-halide (CH 3 NH 3 PbI 3¹x Cl x ) perovskite. 8,9 A precursor solution containing lead iodide (PbI 2 ) or lead chloride (PbCl 2 ) mixed with methylammonium iodide (CH 3 NH 3 I) in N,N-dimethylformamide (DMF) is basically used for forming CH 3 NH 3 PbI 3 or CH 3 -NH 3 PbI 3¹x Cl x , respectively. Both types of perovskite absorber layer have shown promising results. CH 3 NH 3 PbI 3¹x Cl x has been often used to fabricate planar architecture devices with high power conversion efficiency (PCE). 7,10 As the exact content of chloride is not yet known, the chemical formula of CH 3 NH 3 -PbI 3¹x Cl x is being typically used to show that a small amount of chloride salts remains in the device. Several possible locations and the role of chloride ions have been discussed in different studies. According to Snaith et al.,8 chloride ions help in the formation of high quality perovskite films by controlling nucleation and growth of perovskite crystals during the annealing process. Excess of methylammonium and chloride are believed to be evaporated during perovskite film formation and a n...