Page - 102 - in Photovoltaic Materials and Electronic Devices

Figure  2.  XRD  patterns  of  glass  substrates  with  vapor  deposition  of  (A)  a  layer  of  PbI2;  and  (B)  a  layer  of  PbI2  followed  by  a  layer  of  MAI,  repeating  this  step  7  times;  XRD  pattern  of  the  (C)  annealed  7‐time  deposited  PbI2/MAI  layer;  (D)  1‐time  deposited  PbI2  (50  nm  thickness)/MAI  (50  nm  thickness)  layer;  and  (E)  1‐time  deposited  PbI2  (150  nm  thickness)/MAI  (150  nm  thickness)  layer.  Reprinted  from  reference  [77],  Copyright  ©  2015,  Royal  Society  of  Chemistry.    Figure  3.  Crystallographic  (lattice)  planes  (in  gray)  of  tetragonal  MAPbI3.  Reprinted  from  reference  [78],  Copyright  ©  2015,  American  Chemical  Society.  For  PbCl2,  Cl−  was  detached  from  PbCl2  when  the  PbCl2  was  evaporated  on  the  MAI  substrate  [79]  and  all  the  atoms  of  lead  halide  were  dissociated  during  the  crystal  formation  of  the  perovskite  [80].  Figure 3. Crystallographic (lattice) planes (in gray) of tetragonal MAPbI3. Reprintedfromreference [78],Copyright©2015,AmericanChemicalSociety. For PbCl2, Cl´was detached from PbCl2 when the PbCl2 was evaporated on the MAI substrate [79] and all the atoms of lead halide were dissociated during the crystal formation of the perovskite [80]. Thus, except the speed and the way of breaking the lead halide, the following steps should be similar with the one stepmethod(Section3.3) forconvertingPbI2 orPbCl2 withMAIto theperovskite. However, thesituation in thepresenceofMAClmaybedifferent. As lessenergy is neededforMAClthanMAItoundergophasetransitionfromsolidtogas[69], itmay be easier for MACl than MAI to diffuse into the PbI2 and cause the crystallization of perovskite [81]. However, as Cl´ cannot be incorporated into MAPbI3 crystal structure, theMAIandMAClmaycompetewitheachother todetermine theresult crystal, because only MAPbI3 or MAPbCl3 was formed when PbI2 was soaked in 80mMMAI+40mMMAClorin40mMMAI+80mMMACl,respectively[80]. Thus, the incorporation of some amountof MACl managed to modify the morphology of theperovskiteandresulted inbetterperformanceof thesolarcells. 3.3.OneStepDepositionofMAPbI3-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], howevernosuchphase transitionwasobservedforMAPbI3-xClx [83]. Toexplain the 102