Effect of thermal annealing on the optical and morphological properties of (AETH)PbX4 (X = Br, I) perovskite films prepared using single source thermal ablation

Films of the new organic-inorganic hybrid materials AETHPbX(4) (AETH = 1,6-bis[5'-(2"aminoethyl)-2'-thienyl]hexane; X =Br, I) were fabricated. using single source thermal ablation (SSTA). The as-deposited films were optically smooth and nominally amorphous. The progressive effects of annealing on the structural, optical, and morphological properties of the films were monitored using powder X-ray diffraction, optical spectroscopy, and atomic force microscopy (AFM). Short duration postdeposition annealing at mild temperatures resulted in well-crystallized films of the AETHPbX4 hybrid perovskites. It was found that up to some critical annealing temperature (similar to 120 degrees C), the emission wavelength and the exciton absorption of the compounds shifted! to lower energies as the annealing temperature increased. As confirmed with AFM measurements, this shift in optical properties suggests a gradual increase of the grain size with annealing temperature. When the samples were annealed at higher temperatures (> 180 degrees C:) their surface morphology changed dramatically, yielding much rougher surfaces due to substantial grain growth and partial decomposition of the framework (with subsequent loss of the organic component). This work demonstrates that the SSTA method can be combined with postdeposition annealing to fabricate good quality, crystalline organic-inorganic perovskite thin films containing complex organic cations.