The Role of Intrinsic Defects in Methylammonium Lead Iodide Perovskite

Abstract

One of the major merits of CH3NH3PbI3 perovskite as an efficient absorber material for the photovoltaic cell is its long carrier lifetime. We investigate the role of the intrinsic defects of CH3NH3PbI3 on its outstanding photovoltaic properties using density-functional studies. Two types of defects are of interest, i.e., Schottky defects and Frenkel defects. Schottky defects, such as PbI2 and CH3NH3I vacancy, do not make a trap state, which can reduce carrier lifetime. Elemental defects like Pb, I, and CH3NH3 vacancies derived from Frenkel defects act as dopants, which explains the unintentional doping of methylammonium lead halides (MALHs). The absence of gap states from intrinsic defects of MALHs can be ascribed to the ionic bonding from organic-inorganic hybridization. These results explain why the perovskite MALHs can be an efficient semiconductor, even when grown using simple solution processes. It also suggests that the n-/p-type can be efficiently manipulated by controlling growth processes.

Ultrasmooth organic–inorganic perovskite thin-film formation and crystallization for efficient planar heterojunction solar cells

“…The extent of the absorption tail below the band gap is correlated with the degree of electronic disorder within the material, which could originate from thermal fluctuation of the ions composing the material but also from defects of the crystalline structure. Indeed, several recent modelling lines of work reported that defects within CH 3 NH 3 PbI 3 perovskite crystals would result in localized states in the range of a few hundred meV from the extended states of the bands, which will be detected as a broadening of the Urbach tail 34 . Assuming the same level of thermal disorder, the slope of the exponential part of the Urbach tail gives an estimation about the concentration of these defects, in terms of Urbach energy 'E u ' 32,33 .…”

Shape Evolution and Single Particle Luminescence of Organometal Halide Perovskite Nanocrystals

“…Because ARTICLE structural defects are known to play a crucial role in perovskite optical properties, 20,65,66 this weak PL intensity could be attributed to surface defects. In agreement with this idea, CH 3 NH 3 PbI 3 wires and rods made in the presence of the surface passivating n-octylammonium cation have a higher PL QYs of 1.7À1.4%, and their PL lifetimes inversely correlate with their aspect and surface-to-volume ratios (Table 1, see also Supporting Information).…”

Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells

“…The hole concentration continuously decreased from 2.5 Â 10 14 to 4.3 Â 10 13 cm À 3 as the thermal annealing duration increased from 0 to 45 min. We speculate that the perovskite top surfaces or the grain boundaries tended to decompose on thermal annealing, which introduced more n-doping I vacancies 31 and compensated the p-doping in the original perovskite films. This was confirmed by the reduction in work function with Fermi energy moving closer to midgap on thermal annealing, as observed by a previous ultraviolet photoelectron spectroscopy (UPS) study 26 .…”