The fate of excited charge carriers in metal halide perovskite semiconductors is influenced by energetic disorder and defects. Here, photoluminescence (PL) blinking is used to probe metastable nonradiative (NR) centers and the nanoscale energy landscape. Temporal activation of an NR center creates a local region with increased NR recombination. Activation and deactivation of this local PL quenching does not only lead to PL blinking, but also to fluctuations of the PL spectra, if the crystal is inhomogeneous in the sense that the PL emission spectrum is slightly different from one location to another. It resembles the spectral hole-burning technique; however, here the eliminated excited states are chosen by their spatial localization close to the quencher. In MAPbI3, PL spectral fluctuations at low temperature reveal energetic inhomogeneities on the order of 5 to 10 meV. Quenching of the main PL band is often found to correlate with an increase of the low-energetic tail of the PL spectra, which is attributed to partially radiative recombination of charges captured by the NR center. The transition energy of the NR center is found to be only ≈80 meV smaller than the bandgap, implying that the underlying defect cannot be a single mid-bandgap state.
- Den kondenserade materiens fysik
- Fysikalisk kemi