Investigation of Dynamics of Perovskites using Chemically, Spatially and Temporally Resolved 2D Mapping

Abstract

Currently, there is an ongoing strong discussion regarding the nature of organometallic CH3NH3PbI3-xClx perovskites for solar cells. In this work, perovskites have been investigated using chemically, spatially, and temporally resolved measurements. To investigate the carrier dynamics of perovskites, perovskite (CH3NH3PbI3-xClx) films were prepared using hot casting technique in which perovskite (CH3NH3PbI3-xClx) solution was prepared by dissolving equimolar ratios of lead iodide (PbI2, Sigma-Aldrich, 99%) and methylamine hydrochloride (MACl, Sigma-Aldrich) in N, N-dimethylformamide (DMF, Sigma-Aldrich, anhydrous, 99.8%) in 11% concentration. A lower hot-casting temperature (100 °C) resulted in smaller grain size, with typical grain sizes of 1~2µm. Hot-casting temperatures higher than 100 °C produced perovskite samples with larger grains of ~ more than tens of micrometers, which was confirmed by high-resolution scanning electron microscopy (SEM). The PL intensity and peak-position mapping image of submicron-scale were performed using confocal micro-spectroscopy. In-plane spatial resolution of ~380nm was indicated by an objective lens with numerical aperture of 0.7 and a solid-state laser with 405nm wavelength for the excitation. The signal collected by the objective lens was detected by a thermoelectrically cooled CCD detector. For the analysis of time resolved PL (TRPL), multifunctional confocal microscopy including a time-correlated single photon counting (TCSPC) system was employed. In addition, 2-D energy-dispersive X-ray (EDS) measurement was performed to elucidate the distribution of chemistries for the surface of perovskites, which were correlated to spatially and temporally resolved PL. Particularly, the carrier dynamics between grain interiors and grain boundaries were systematically investigated.