Photon Recycling in CsPbBr₃ All-Inorganic Perovskite Nanocrystals

Abstract

Photon recycling, the iterative process of re-absorption and re-emission of photons in an absorbing medium, can play an important role in the power-conversion efficiency of photovoltaic cells. To date, several studies have proposed that this process may occur in bulk or thin films of inorganic lead-halide perovskites, but conclusive proof of the occurrence and magnitude of this effect is missing. Here, we provide clear evidence and quantitative estimation of photon recycling in CsPbBr 3 nanocrystal suspensions by combining measurements of steady-state and time-resolved photoluminescence (PL) and PL quantum yield with simulations of photon diffusion through the suspension. The steady-state PL shows clear spectral modifications including red shifts and quantum yield decrease, while the time-resolved measurements show prolonged PL decay and rise times. These effects grow as the nanocrystal concentration and distance traveled through the suspension increase. Monte Carlo simulations of photons diffusing through the medium and exhibiting absorption and re-emission account quantitatively for the observed trends and show that up to five re-emission cycles are involved. We thus identify 4 quantifiable measures, PL red shift, PL QY, PL decay time, and PL rise time that together all point toward repeated, energy-directed radiative transfer between nanocrystals. These results highlight the importance of photon recycling for both optical properties and photovoltaic applications of inorganic perovskite nanocrystals.

Strongly Confined CsPbBr3 Quantum Dots as Quantum Emitters and Building Blocks for Rhombic Superlattices

“…We suggest that elucidating the precise relationship between SL strain and PL properties (here: spectrum and lifetime) may require the careful exclusion of several alternative potential origins, e.g. , size and shape segregation within the SL, self-absorption, − exciton diffusion, − and photon propagation and recycling effects. − …”

Synthesizing Bright CsPbBr3 Perovskite Nanocrystals with High Purification Yields and Their Composites with In Situ-Polymerized Styrene for Light-Emitting Diode Applications

“…When the bulk composite is thinner or ground into powders, the PLQY increases owing to the reduced photon recycling probability (Figure S9b). The highest PLQY reached is 77% corresponding to the CTAB-CsPbBr 3 @PS thin film synthesized at 60 °C for 1 h (this condition is applied for the composites mentioned below, unless otherwise noted), which is much higher than 21% of the OA/OAm-CsPbBr 3 @PS composite (Figure b). Table S3 summarizes the synthetic and performance parameters of some reported CsPbBr 3 @polymer composites fabricated via polymerization.…”

Electronic Coupling of Highly Ordered Perovskite Nanocrystals in Supercrystals

“…We have performed absorption and PL measurements for different dilutions (up to 100 times) of the SB suspensions in order to exclude any reabsorption effect ( Figure S4b,c ), as this could also give an apparent red shift. 22 After drop-casting on the quartz substrate, the absorption and PL spectra of the SBs film are also similar to the colloidal solution ( Figure S4d ). Finally, we point out that the red shift is likely not due to superfluorescence, as it is not expected to survive thermal disorder at room temperature.…”

“…This is further supported by the larger photon energy, although moderately, than that reported for bulk perovskites. , Also high-resolution SEM images (Figure S2) show that the NCs in the SBs are clearly separated, displaying crystalline ordering and no coalescence of NCs. We have performed absorption and PL measurements for different dilutions (up to 100 times) of the SB suspensions in order to exclude any reabsorption effect (Figure S4b,c), as this could also give an apparent red shift . After drop-casting on the quartz substrate, the absorption and PL spectra of the SBs film are also similar to the colloidal solution (Figure S4d).…”