Chloride in Lead Chloride-Derived Organo-Metal Halides
for Perovskite-Absorber Solar Cells
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Abstract
Organo-metal
halide perovskites are an intriguing class of materials
that have recently been explored for their potential in solar energy
conversion. Within a very short period of intensive research, highly
efficient solar cell devices have been demonstrated. One of the heavily
debated questions in this new field of research concerns the role
of chlorine in solution-processed samples utilizing lead chloride
and 3 equiv of methylammonium iodide to prepare the perovskite samples.
We utilized a combination of X-ray photoelectron spectroscopy, X-ray
fluorescence, and X-ray diffraction to probe the amount of chlorine
in samples before and during annealing. As-deposited samples, before
annealing, consist of a crystalline precursor phase containing excess
methylammonium and halide. We used in situ techniques to study the
crystallization of MAPbI<sub>3</sub> from this crystalline precursor
phase. Excess methylammonium and chloride evaporate during annealing,
forming highly crystalline MAPbI<sub>3</sub>. However, even after
prolonged annealing times, chlorine can be detected in the films in
X-ray fluorescence measurements