Page - 103 - in Photovoltaic Materials and Electronic Devices

absence of the phase transition for MAPbI3-xClx, we first study the crystallization processofMAPbI3-xClx byonestepdepositionmethod. resulted  in  better  performance  of  the  solar  cells.    3.3.  One  Step  Deposition  of  MAPbI3‐xClx  The  better  crystallization  of  MAPbI3‐xClx  along  (110)  and  (220)  plane  of  the  tetragonal  phase  or  (100)  and  (200)  planes  of  the  cubic  phase  may  be  due  to  the  lowered  cubic‐tetragonal  phase  transition  temperature  of  MAPbI3−xClx  after  the  incorporation  of  Cl−  [82].  A  clear  cubic‐tetragonal  phase  transition  temperature  of  MAPbI3  was  detected  by  differential  scanning  calorimeter  (DSC)  analysis  [65],  however  no  such  phase  transition  was  observed  for  MAPbI3−xClx  [83].  To  explain  the  absence  of  the  phase  transition  for  MAPbI3−xClx,  we  first  study  the  crystallization  process  of  MAPbI3‐xClx  by  one  step  deposition  method.    Figure  4.  XRD  patterns  and  optical  images  (insets)  of  MAPbI3‐xClx  film  during  annealing.  Reprinted  from  reference  [84],  Copyright  ©  2015,  American  Chemical  Society.  Detail  information  about  crystal  formation  process  of  MAPbI3  is  summarized  in  reference  [85].  For  MAPbI3‐xClx,  the  transformation  from  the  intermediate  phase  to  the  perovskite  is  determined  as  Figure 4. XRD patterns and opt cal i ages (insets) of MAPbI3-xClx film during annealing. Reprinted from reference [84], Copyright © 2015, American ChemicalSociety. Detail informationaboutcrystal formationprocessofMAPbI3 is summarized inreference [85]. ForMAPbI3-xClx, the transformationfrom the intermediatephase to the perovskite is determined as 80 ˝C by in situgrazing incidence wide-angle X-ray scattering (GIWAXS) [86]. Figure 4 presents a clearer picture of the crystal formationofMAPbI3-xClx. The15.7˝and31.5˝peaksareassociatedwiththe(100) and (200) diffraction peaks of MAPbCl3 [82]. These peaks were also observed in references [27,87,88]. In Figure 4, it is interesting to note that MAPbI3 was formed first for theas-spincoatedfilmbutconvertedtoMAPbCl3 afterannealingat100˝C for 10 min, and then MAPbCl3 was converted back to MAPbI3 after 45 min of annealing[84]. Furtherannealingwouldresult in thedecompositionofMAPbI3 to PbI2, but this occurred after conversion to the intermediate phase to MAPbI3 [89]. Because MAPbCl3 is in a cubic phase, we suppose that MAPbCl3 may cause a templateeffect for thecubicMAPbI3 phase. 103