Solution-processed organic−inorganic and all-inorganic lead halide perovskite semiconductors have rapidly progressed as versatile and promising materials for a number of optoelectronic applications. Facile solution processing allows for various nano- and microstructures to be fabricated out of perovskite materials of different compositions. The optimization of the performance of potential devices would critically depend on the assessment and understanding of fundamental photophysical properties and processes in perovskites and their dependence on the composition. The intrinsic quantum yield of the photon emission and the character of the emission processes: e.g., free electron-hole recombination vs. excitonic recombination, are among such fundamental properties. Related to them is the nature of the long-range spatial propagation of photoexcitations, which might occur via diffusion of charge carriers and via reabsorption of photons emitted during recombination (photon recycling).

In this work, we use time- and spectrally-resolved double-objective photoluminescence (PL) spectroscopy to directly demonstrate photon reabsorption taking place in cesium-based lead halide perovskite microwires of different compositions, including CsPbBr₃ [1]. We vary the spatial separation between the excitation and collection objectives focused on a single microwire and observe the appearance of time-delayed PL emission at separations exceeding 100 microns from the excitation spot. In independent measurements, we find that the mobility of charge carriers in the studied materials is low enough for the charge carrier diffusion to be irrelevant for observed spatiotemporal evolution of PL. As the separation increases, the data shows a clear pattern of the rise times in PL dynamics thus signifying its origin in the photon reabsorption assisted by the emitted light trapping in the microwire waveguides. We also observe the PL spectrum developing red shifts increasing with the separation. The details of these signatures are found to depend on the composition of the wire material. We observe that the composition can dramatically alter the excitation power dependence of the PL: from the power dependence corresponding to free electron-hole recombination to the one corresponding to the excitonic (or geminate) recombination.

We compare experimental data to the results of a quantitative kinetic model developed to account for contributions of mono- and bimolecular recombination in the presence of waveguide-assisted emission-reabsorption events. This comparison enables us to assess the intrinsic quantum yield of elementary radiative recombination events.