Low-Temperature Emission Dynamics of Methylammonium Lead Bromide Hybrid Perovskite Thin Films at the Sub-Micrometer Scale

Abstract

We study the low-temperature (T = 4.7 K) emission dynamics of a thin film of methylammonium lead bromide (MAPbBr3), prepared via the anti-solvent method. Using intensity-dependent (over 5 decades) hyperspectral microscopy under quasi-resonant (532 nm) continuous wave excitation, we revealed spatial inhomogeneities in the thin film emission. This was drastically different at the band-edge (∼550 nm, sharp peaks) than in the emission tail (∼568 nm, continuum of emission). We are able to observe regions of the film at the micrometer scale where emission is dominated by excitons, in between regions of trap emission. Varying the density of absorbed photons by the MAPbBr3 thin films, two-color fluorescence lifetime imaging microscopy unraveled the emission dynamics: a fast, resolution-limited (∼200 ps) monoexponential tangled with a stretched exponential decay. We associate the first to the relaxation of excitons and the latter to trap emission dynamics. The obtained stretching exponents can be interpreted as the result of a two-dimensional electron diffusion process: Förster resonant transfer mechanism. Furthermore, the non-vanishing fast monoexponential component even in the tail of the MAPbBr3 emission indicates the subsistence of localized excitons. Finally, we estimate the density of traps in MAPbBr3 thin films prepared using the anti-solvent method at n∼1017 cm−3.

High-Responsivity Planar Photodetector Based on Methylammonium Lead Bromide Perovskite Thin Film

“…The photoluminescence measurement (Figure 2b) shows strong emission peaking at 530 nm with 20 nm full width half maximum. The shoulder peaks at around 550 nm can potentially be attributed to active sub-bandgap defects, which are detected at wavelengths as long as 600 nm [32][33][34]. For the absorption spectrum (Figure 2a), the absorption exhibits an exciton peak at 521 nm, as expected from similar MAPbBr 3 thin films [35].…”

“…We present in Figure 3e the detected photocurrent as a function of the cut-off wavelength of the long-pass filters at 1 V using the lamp spectra presented in Figure 3c at 0.125 W/cm 2 light excitation intensity. The non-zero photocurrent detected for a cut-on wavelength at 600 nm is a signature of active sub-bandgap defects and intrinsic disorder in the Urbach tail of MAPbBr 3 , defects are detected at wavelengths as long as 600 nm [31][32][33][34]37]. The responsivities R at 4 V and 0.125 W/cm 2 light excitation intensity have been extracted for three different wavelength ranges of excitations.…”