Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
Lead-halide perovskites have emerged as promising semiconductors for optoelectronic applications, especially for efficient solar cells. However, these cells show hysteresis in the current-voltage curves, and their stability with respect to water exposure is problematic. Furthermore, several studies emphasized light-induced structural rearrangements. These issues are possibly related to defect migration occurring in the perovskite material.
Here, we present our first-principles results on defect migration phenomena in hybrid and all-inorganic lead-halide crystals.[1,2] Our calculations are based on dispersion-corrected density functional theory and nudged-elastic band methods to optimize minimum energy pathways of defect species.
First, the migration of hydrogen interstitials will be discussed,[1] which are important for prototypical semiconductors, ranging from inorganic materials such as ZnO to organic ones, and also oxide perovskites. We find that in MAPbI3 proton motion is supported by the mechanical flexibility of the lead-halide framework and activation energies for their migration are small, indicating mobile hydrogen interstitials at room temperature. Furthermore, differently charged defects occupy opposite sites in MAPbI3, which allows for ionization-enhanced defect migration following the Bourgoin-Corbett mechanism.
Second, we present our results on migration and anion-exchange reactions of interstitial Cl in all-inorganic CsPbI3,[2] which facilitates chloride doping at levels near the solubility limit for chloride in cesium lead iodide. We achieve this experimentally by co-depositing cesium lead halide nanocrystals and using chemically-induced room-temperature sintering. The resulting polycrystalline film has a Cl:I ratio of a few percent in the mixed phase. At these incorporation levels, the half-life of the functional phase in a humid atmosphere increases by more than an order of magnitude compared to the undoped CsPbI3 film.
[1] David A. Egger, Leeor Kronik, Andrew M. Rappe, Angew. Chem. Int. Ed., 54, 12437–12441 (2015).
[2] Subham Dastidar, David A. Egger, Liang Z. Tan, Samuel B. Cromer, Andrew D. Dillon, Shi Liu, Leeor Kronik, Andrew M. Rappe, Aaron T. Fafarman, Nano Lett., available online, DOI: 10.1021/acs.nanolett.6b00635.
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