Identification of lead vacancy defects in lead halide perovskites

Abstract

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 1015 cm−3 was determined. There was also evidence of trapping at the vacancy complex $$({{{{{\rm{V}}}}}}_{{{{{\rm{Pb}}}}}}{{{{{\rm{V}}}}}}_{{{{{\rm{I}}}}}})^{-}$$ ( V Pb V I ) − in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, $${{{{{{\rm{V}}}}}}}_{{{{{{\rm{Pb}}}}}}}^{2-}$$ V Pb 2 − , point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.

Strain effects on halide perovskite solar cells

“…Metal halide perovskites are highly defect tolerant as bonding and anti-bonding orbitals mostly reside within the bands. Nevertheless, intrinsic defects such as interstitial halide, halide vacancy, and lead vacancy can accompany the formation of either deep or shallow trap states, 80,81 which are responsible for the material degradation and deterioration of structural stability due to ionic nature of halide perovskites. 82 Recent studies have shown influence in point defect densities while the perovskites experience strains.…”

Symmetrical Acceptor–Donor–Acceptor Molecule as a Versatile Defect Passivation Agent toward Efficient FA0.85MA0.15PbI3 Perovskite Solar Cells

“…[ 31 ] Additionally, thermogravimetric analysis shows a stable IDT‐OD molecule even at high temperature of ≈390 °C (Figure S6, Supporting Information), suggesting that the traditional annealing process of 150 °C cannot cause molecular decomposition. The X‐ray photoelectron spectroscopy (XPS) full spectrum of the annealed perovskite (Figure S7, Supporting Information) also proves the anticipation that the molecules remaining in the film can passivate the uncoordinated Pb 2+ and I − at grain boundaries or perovskite film surface, reducing the probability of nonradiative recombination, [ 32–34 ] which is conducive to the separation and transport of charge.…”

Superhalogen Passivation for Efficient and Stable Perovskite Solar Cells

“…[ 10 ] However, the shallow‐level defects may also be problematic as they can lead to the formation of polarons that may activate the nonradiative process degrading the photovoltaic performance of PSCs. [ 11 ] Several studies have revealed that interstitial iodide and iodide vacancy are responsible for the formation of deep‐, and shallow‐level trap states, respectively, [ 12,13 ] and their high density in perovskites due to the low formation energy may result in more serious degradation of the material's optoelectronic properties and stability. Moreover, the most active migrating species is known to be iodide with a low activation energy of migration.…”