“Supertrap” at Work: Extremely Efficient Nonradiative Recombination Channels in MAPbI₃ Perovskites Revealed by Luminescence Super-Resolution Imaging and Spectroscopy

Abstract

Organo-metal halide perovskites are some of the most promising materials for the new generation of low-cost photovoltaic and light-emitting devices. Their solution processability is a beneficial trait, although it leads to a spatial inhomogeneity of perovskite films with a variation of the trap state density at the nanoscale. Comprehending their properties using traditional spectroscopy therefore becomes difficult, calling for a combination with microscopy in order to see beyond the ensemble-averaged response. We studied photoluminescence (PL) blinking of micrometer-sized individual methylammonium lead iodide (MAPbI) perovskite polycrystals, as well as monocrystalline microrods up to 10 μm long. We correlated their PL dynamics with structure employing scanning electron and optical super-resolution microscopy. Combining super-resolution localization imaging and super-resolution optical fluctuation imaging (SOFI), we could detect and quantify preferential emitting regions in polycrystals exhibiting different types of blinking. We propose that blinking in MAPbI occurs by the activation/passivation of a "supertrap" which presumably is a donor-acceptor pair able to trap both electrons and holes. As such, nonradiative recombination via supertraps, in spite being present at a rather low concentrations (10-10 cm), is much more efficient than via all other defect states present in the material at higher concentrations (10-10 cm). We speculate that activation/deactivation of a supertrap occurs by its temporary dissociation into free donor and acceptor impurities. We found that supertraps are most efficient in structurally homogeneous and large MAPbI crystals where carrier diffusion is efficient, which may therefore pose limitations on the efficiency of perovskite-based devices.

Creation and Annihilation of Nonradiative Recombination Centers in Polycrystalline Metal Halide Perovskites by Alternating Electric Field and Light

“…Generally speaking, nonradiative recombination occurs via charge trapping by defect states lying close to the middle of the bandgap, by nonradiative centers of a complex internal organization (like, e.g., donor-acceptor pairs) and by surface states. [37][38][39] For MAPbI 3 , the most widely discussed native point defects are iodine vacancies (V I ) and anti-site occupations (Pb I and I MA ). [20][21][22][23] Frenkel defects (the simplest defect complex consisting of an interstitial defect and a vacancy created by the same atom) have also been discussed as possible effective nonradiative centers.…”

Super‐resolution Fluorescence Imaging for Materials Science

“…More recently, organometal halide perovskites (OHPs) have been the subject of a growing number of super‐resolution studies . OHPs have recently emerged as novel photovoltaic materials showing record‐breaking performance.…”

“…Individual OHP nanoparticles showed strong PL blinking and super‐resolution localization pinpointed their emission to the center of the nanoparticle ( Figure ). [81b] For polycrystalline OHP films, super‐resolution mapping of the PL enabled sensitive detection of nanodomains. [81c] As this blinking behaviour is closely linked to the (transient) nature and type of trapping sites, mapping of PL blinking yields functional information of these materials at the nanoscale.…”

“…[81b] For polycrystalline OHP films, super‐resolution mapping of the PL enabled sensitive detection of nanodomains. [81c] As this blinking behaviour is closely linked to the (transient) nature and type of trapping sites, mapping of PL blinking yields functional information of these materials at the nanoscale. Due to the sensitivity of these materials to environmental parameters, strict atmospheric control during the measurements was shown to be of critical importance.…”

“…Due to the sensitivity of these materials to environmental parameters, strict atmospheric control during the measurements was shown to be of critical importance. [81b]…”