Determination of Chloride Content in Planar CH3NH3PbI3−xClx Solar Cells by Chemical Analysis

Abstract

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...

Fabrication and Characterization of CH3NH3PbI3−x−yBrxCly Perovskite Solar Cells

“…The effects of halogen doping and HTL on photovoltaic properties and microstructure on organic-inorganic hybrid heterojunction solar cells using the perovskite compound have been studied for improving photovoltaic performance and optical properties. In particular, the influence of halogen doping on iodide, bromine and chlorine halide perovskite structures in the hybrid solar cells have been characterized for optimizing band gap, crystal structure, optical and photovoltaic properties and conversion efficiency [11][12][13]. The role of halogen doping using iodine (I), bromine (Br) and chlorine (Cl) compounds as the dopant and the HTL on the photovoltaic and structural properties is an important factor to optimize the improvement of carrier-generation, carrier diffusion, transporting properties and photovoltaic performance.…”

“…The role of halogen doping using iodine (I), bromine (Br) and chlorine (Cl) compounds as the dopant and the HTL on the photovoltaic and structural properties is an important factor to optimize the improvement of carrier-generation, carrier diffusion, transporting properties and photovoltaic performance. Quantitative investigation into the photovoltaic and optical properties of the perovskite structure with molar ratio dependence of I, Cl and Br compounds has been performed [13]. Control of halogen doping with molar ratio between I, Cl and Br in perovskite crystal structure will provide the best condition for the photovoltaic performance, the crystal structure, carrier mobility and electronic electronic structure with band gaps between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and the optical properties with a wide range of absorption.…”

Temperature Effects on the Photovoltaic Performance of Planar Structure Perovskite Solar Cells

“…After annealing the perovskite layer, the final compound formed is essentially CH 3 NH 3 PbI 3 , although a trace amount of chloride can be found in the device. 16 Finally, the hole transport layer was deposited on the perovskite layer.The XRD pattern of CH 3 NH 3 PbI 3 without bias voltage in the dark was measured under standard conditions at room temperature ( Figure S1). The characteristic peaks at 14.1, 28.5, and 43.3°are attributed to the (110), (220), and (330) planes confirm the tetragonal I4/mcm space group at room temperature.…”

Direct Confirmation of Distribution for Cl−in CH3NH3PbI3−xClxLayer of Perovskite Solar Cells

“…It has been proved by different chemical analysis methods such as titration or ion chromatography that a trace amount of chloride can be still found in the device. 6,8 The chemical formula CH 3 NH 3 PbI 2.94 Cl 0.06 with a chloride content of less than 2% from the total halide ions has been proposed. 6 Pool et al 9 also found x = 0.05 for their annealed perovskite films.…”

“…6,8 The chemical formula CH 3 NH 3 PbI 2.94 Cl 0.06 with a chloride content of less than 2% from the total halide ions has been proposed. 6 Pool et al 9 also found x = 0.05 for their annealed perovskite films. In the case of Li et al, 8 x = 0.17 was estimated by potentiometric titration.…”