Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr₃ Nanowires as a Model System

Abstract

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr 3 nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr 3 nanowires, an ambipolar carrier mobility of μ = 35 cm 2 V −1 s −1 is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.

Recycled Photons Traveling Several Millimeters in Waveguides Based on CsPbBr3 Perovskite Nanocrystals

“…To explain these results, we have first quantified the effect of PR as a feedback mechanism for carriers introduced in a rate equation model indicating that the PR effect could be interpreted as gain, but leading to compensation of losses during propagation. However, although a set of rate equations are usually chosen to theoretically predict the consequences of the PR effect, [6,18,[23][24][25][26] they cannot easily incorporate the evolution of the photons with the propagation distance and the effect of the reabsorption in the shape of the PL spectrum. For this reason, we proposed a stochastic Monte Carlo model that reproduces both such experimental PL redshift and delay time introduced by photon reabsorption/reemission events during propagation in the PR effect.…”

“…In this way, over the last 3–4 years, different experimental and theoretical reports have analyzed the efficiency of PR in HPs and the potential benefits in solar cells [ 13–15 ] or light‐emitting diodes, [ 15,16 ] among other devices. 15 In particular, experimental studies carried out in CH 3 NH 3 PbX 3 (X = Cl, Br, I) polycrystalline thin films, [ 17,18 ] CH 3 NH 3 PbX 3 single crystals, [ 10,19,20 ] CsPbBr 3 nano/microwires [ 21–23 ] or CsPbBr 3 nanocrystals [ 9 ] always show that PL spectra experience an important redshift and an elongation of the decay time after traversing some microns of the HP material. Although there has been a controversy about the impact of PR in the total PL spectra, [ 19,24 ] or if PR dominates or not over carrier diffusion on the effective decay time, [ 23,25 ] recent studies on perovskite single crystals [ 6 ] and MAPI polycrystalline thin films [ 18 ] confirm that PR is the dominant transport mechanism for propagation lengths longer than the diffusion of carriers.…”

“…15 In particular, experimental studies carried out in CH 3 NH 3 PbX 3 (X = Cl, Br, I) polycrystalline thin films, [ 17,18 ] CH 3 NH 3 PbX 3 single crystals, [ 10,19,20 ] CsPbBr 3 nano/microwires [ 21–23 ] or CsPbBr 3 nanocrystals [ 9 ] always show that PL spectra experience an important redshift and an elongation of the decay time after traversing some microns of the HP material. Although there has been a controversy about the impact of PR in the total PL spectra, [ 19,24 ] or if PR dominates or not over carrier diffusion on the effective decay time, [ 23,25 ] recent studies on perovskite single crystals [ 6 ] and MAPI polycrystalline thin films [ 18 ] confirm that PR is the dominant transport mechanism for propagation lengths longer than the diffusion of carriers. Besides, the theoretical analysis predicts that multiple absorption and emission processes produce a certain “diffusive regime of traveling photons” that increases the effective lifetime of photons outcoupled from the sample (thin film, microwire, single crystal …).…”

Simultaneous Synthesis, Modification, and DFT Calculation of Three‐Color Lead Halide Perovskite Phosphors for Improving Stability and Luminous Efficiency of WLEDs

“…In recent years, the metal halide perovskite with the general formula ABX 3 has become one of the most promising materials for solution-processable LED technology due to its high absorption coefficient, adjustable bandgap energy, and high photoluminescence quantum yield (PLQY). [17][18][19][20][21] Among them, the all-inorganic metal halide perovskite CsPbX 3 (X = Cl, Br, I) can be used as a green light-emitting element in WLED to improve the device performance due to its high color purity, high defect tolerance, and bright PL emission. [22][23][24][25][26] However, it is well known that CsPbBr 3 is prone to deterioration and it has poor thermal stability when exposed to the air for a long time.…”

“…However, the shortcoming of poor stability directly affects the luminous performance of the WLED devices and reduces their luminous efficiency, which has become an urgent problem to be solved. Here, three-color lead halide perovskite phosphors (blue-emitting CsPbBr 3 synthesized at 20 including combining it with MOF and surface coatings. [27][28][29][30][31] These methods can indeed improve the stability, but also have a slight impact on the luminous intensity of the material.…”