Tuning morphological features of lead iodide by low pressure vapor phase deposition

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

THIN SOLID FILMS

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2018

0040-6090

Lead iodide (PbI2) is a semiconductor with extensive use as an active layer for X-ray detectors and as a precursor for perovskite solar cells. Here we present a low vacuum method to obtain very uniform PbI2 films with full substrate coverage. This method consists in the sublimation of PbI2 inside  a  hot  zone  and  its  transport  by  an  Arflow  to  a  substrate  held  at  a  controlled temperature. Using scanning electron microscopy combined with focused ion beam and X-ray diffraction  we  studied  the  morphology  and  crystallographic  structure  of  the  PbI2 films with different  deposition  parameters:  substrate  and  source  evaporation  temperature,  deposition time  and  substrate  material.  At high  substrate  temperature  (80ºC)  and  low  evaporation temperature (310ºC) onto a glass sample, we obtained dense and smooth PbI2 films showing hexagonal  crystals,  or  platelets,  stacked  parallel  to  the  substrate. The  choice  of  the  substrate material has a significant impact on the film morphology yielding porous-like structures with voids  within  the  films  for some  substrates. A bandgap Eg = 2.42  eV and  Urbach energy EU = 82.6  meV were  obtained  by  absorbance  measurements,  which  are  comparable  to  films 2 evaporated in high vacuum. Photoluminescence studies showed a dependence of the emission energies  on  the crystal  orientation  of  the platelets which grow differently depending  on the deposition conditions. The results show the ability of the low pressure vapor phase deposition technique to obtain good film properties, suitable for sensors and optoelectronic devices.