LOW PRESSURE VAPOR PHASE DEPOSITION AS A METHOD TO OBTAINING PBI2 FILMS FOR TWO STEP CONTROLLED SYNTHESIS OF PEROVSKITES

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

Oxford

Conferencia; 3rd International Conference on Perovskite Solar Cells and Optoelectronics; 2018

University of Oxford

Lead iodideis a wide-gap semiconductor with interesting electro-optical properties thathas been receiving a great deal of attention due to its application in thesynthesis of perovskite solar cells. Perovskites films have been prepared by anumber of different deposition techniques, mostly from the precursors insolution, with some effort dedicated to the evaporation processes [1]. In particular,low pressure vapor phase deposition (LP-VPD) arises as a promising techniquethat allows high control of the films morphology byfine tuning the different deposition variables while reducing the material waste[2,3]. The LP-VPD method relies on the sublimation of a substance under low vacuum byan inert carrier gas transport, from the hot region towards the cold zone. In this work we implement an experimentalsetup which comprises a four-temperature zones gradient that allows precisecontrol of the LP-VPD deposited films. We present a preliminary study of the preparation of lead iodide films bythe LP-VPD method as means to further study the perovskite formation and theimpact of PbI2 morphology into the synthesis of large perovskitecrystals. The ability of fine tuning the films' structural properties isevaluated by modification of the substrate material, deposition time, and evaporationtemperature[F1] . The films were characterized byelectronic microscopy (SEM), x-ray diffraction (XRD), global reflectance (R)and transmittance (T) in the visible spectrum and room temperaturephotoluminescence (PL) spectrometry.Welldefined hexagonal crystals, or platelets with hcp crystal structure were obtainedfor all samples. Such structures have been reported earlier for VPD under caredconditions [4]. Films grown on glass at high substrate temperatures (80ºC) andlow evaporation temperatures (310ºC) show highly oriented platelets with apreferential (001) orientation parallel to the substrate. Lower substratetemperatures (40ºC) yielded non-parallel platelets, which produced voids withinthe films. PL spectra show signal variations with temperature and time tuningthat can be related to structural changes. From RT measurements the absorptioncoefficient, the Urbach energy and the band gap were obtained and compared toliterature values.