Lead iodide thin films deposited by low pressure vapor phase deposition with controlled morphology

SOLDERA, FLAVIO; PÉREZ, M. DOLORES; KOFFMAN-FRISCHKNECHT, ALEJANDRO; TROVIANO, MAURICIO; TARETTO, KURT R.; SOLDERA, MARCOS; CARLOS, LUCIANO

Darmstadt

Conferencia; Materials Science and Engineering; 2018

DGM

Lead iodide (PbI2) is a wide-gap semiconductor with interesting electro-optical properties for applications such as X-ray detectors [1]. Recently, this material has received great attention as a precursor for obtaining metal organic perovskite solar cells [2]. One of the most common perovskites is obtained from the reaction between PbI2 and methylammonium iodide (MAI) that yields the molecule CH3NH3PbI3. Typically, this perovskite is obtained by exposing a PbI2 film to MAI from the liquid or vapor phase using a wide variety of techniques [3]. Some studies suggest that the morphology of PbI2 film influences its reaction with MAI [4]. Here, we use the low pressure vapor phase deposition method [5] to prepare PbI2 films with controlled morphology. This method relies on the sublimation of a compound in low vacuum and its transport by an inert gas towards a cooler zone where a substrate is placed. Since the chamber walls are kept at temperatures higher than the sublimation temperature, the vapor condenses only onto the cooled substrate, yielding a very efficient material usage. We study the tuning capability of structural properties by modifying the substrate material, deposition time, evaporation and substrate temperatures. The films were characterized by means of electronic microscopy (SEM/FIB), x-ray diffraction, and global reflectance (R) and transmittance (T) in the visible spectrum.Well defined hexagonal crystals with hcp crystal structure were grown in all our experiments, which was expected from previous works [6]. Films grown on glass at high substrate temperatures (80ºC) and low evaporation temperatures (310ºC) have shown very oriented platelets with a preferential orientation (001) parallel to the substrate. Lower substrate temperatures (40ºC) yielded non-parallel platelets, which produced voids within the films. From RT measurements, Urbach energy and band gap were obtained and compared to literature values.In summary this deposition technique allowed us to obtain crystalline, uniform films with controlled morphology and standard optical properties.References[1] K. S. Shah et al., Nucl. Instr. Meth. Phys. Res. (1996), 380, 266. [2] M.A. Green, and A. Ho-Baillie, ACS Energy Lett. (2017), 2, 822[3] G. Pellegrino at al., J. Phys. Chem. C. (2016), 120, 19768.[4] F. Fu et al., Phys. Status Solidi A (2015), 212, 2708.[5] Burrows, P. E. et al., J. Cryst. Growth (1995), 156, 91.[6] Schieber, M. et al., J. Cryst. Growth (2008), 310, 3168.