Halide Vacancies Create No Charge Traps on Lead Halide Perovskite Surfaces but Can Generate Deep Traps in the Bulk

JY Ran and BP Wang and YF Wu and DY Liu and CM Perez and AS Vasenko and OV Prezhdo, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 14, 6028-6036 (2023).

DOI: 10.1021/acs.jpclett.3c01231

Metal halide perovskites (MHPs) have attracted attentionbecauseof their high optoelectronic performance that is fundamentally rootedin the unusual properties of MHP defects. By developing an ab initio- basedmachine-learning force field, we sample the structural dynamics ofMHPs on a nanosecond time scale and show that halide vacancies createmidgap trap states in the MHP bulk but not on a surface. Deep trapsresult from Pb-Pb dimers that can form across the vacancy inonly the bulk. The required shortening of the Pb-Pb distanceby nearly 3 & ANGS; is facilitated by either charge trapping or 50ps thermal fluctuations. The large-scale structural deformations arepossible because MHPs are soft. Halide vacancies on the MHP surfacecreate no deep traps but separate electrons from holes, keeping thecharges mobile. This is particularly favorable for MHP quantum dots,which do not require sophisticated surface passivation to emit lightand blink less than quantum dots formed from traditional inorganicsemiconductors.

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