Rutherford Backscattering Spectroscopy of Mass Transport by Transformation of PbI2 into CH3NH3PbI3 within np TiO2

Abstract

Mass transport during transformation of PbI2 infiltrated in nanoporous TiO2 into CH3NH3PbI3 has been investigated by Rutherford backscattering spectroscopy RBS . Fast initial reaction kinetics were confirmed using optical ex situ and in situ measurements. Mapping with energy dispersive X ray spectroscopy of the cross section of samples revealed a homogeneous PbI2 infiltration in nanoporous TiO2 before transformation but an accumulation of Pb and I at the surface after transformation, in accordance with a depletion of Pb and I in a near surface region. Quantitative depth profiles of Pb and I were obtained from RBS analysis. An instant degradation of CH3NH3PbI3 to PbI2 and volatiles upon ion radiation was found. The concentration profiles of Pb could be simulated with a one dimensional diffusion model taking into account an effective diffusion coefficient of Pb in the nanocomposite about 1.5 amp; 8901;10 11 cm2 s as well as a parameter considering frazzling at the surface due to formation of crystallite