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Formation of Color Centers in Lead Iodide Perovskites: Self-Trapping and Defects in the Bulk and Surfaces
journal contribution
posted on 2020-08-06, 22:00 authored by Francesco Ambrosio, Edoardo Mosconi, Ahmed A. Alasmari, Fatmah A. S. Alasmary, Daniele Meggiolaro, Filippo De AngelisSelf-trapping of
excitons or of free charges associated with the
formation of color centers is typical of conventional halides. By
analogy, lead halide perovskites could in principle show self-trapping
of photogenerated charge carriers, possibly leading to defect formation
and long-term material instability. Here we investigate the energetics
of hole self-trapping in methylammonium lead iodide (MAPbI3) by performing first-principles electronic structure calculations.
The thermodynamics and kinetics for the formation of bridging I2– dimers and iodine vacancy/I3– trimer Frenkel defects, originated by self-trapping
of one and two holes, respectively, are investigated both in the bulk
and at selected surfaces, in both pristine and defective systems.
Our results indicate that hole self-trapping is unlikely to occur
in the bulk, being thermodynamically unfavorable with associated high-energy
barriers. Self-trapping remains unfavorable at surfaces, though it
is significantly stabilized compared to the bulk. The inclusion of
typical hole-trapping defects, such as the lead vacancy and the interstitial
iodine, further stabilizes the formation of color centers, which eventually
become stable for the PbI2-terminated MAPbI3 surface. Overall, our results clearly indicate that surfaces and
grain boundaries are the main instability sources in lead iodide perovskites
and that tailoring surface passivation is crucial for improving the
performance and long-term stability of devices based on lead halide
perovskites.