EN
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 10-11 cm2/s) as well
as a parameter considering frazzling at the surface due to
formation of crystallites.