Phonon Coupling with Excitons and Free Carriers in Formamidinium Lead Bromide Perovskite Nanocrystals

Abstract

Organometal halide perovskites in the form of nanocrystals (NCs) have attracted enormous attention due to their unique optoelectronic and photoluminescence (PL) properties. Here, we examine the phase composition and the temperature dependence of emission line width broadening in formamidinium lead bromide (FAPbBr) perovskite nanocrystals (NCs) for light-emitting applications and identify different charge-carrier scattering mechanisms. Our results show most of the emission is from the orthorhombic phase. The PL line width broadening at high temperature is dominated by the Fröhlich interaction between the free charge carriers and the optical phonons. At low temperatures, the peak of the PL spectrum exhibits a continuous red shift indicating an increase of excitons contribution at lower temperatures, and concurrently the line width also narrows down due to the inhibition of the optical phonons. From the temperature-dependent measurements, the coupling strength of both the charge phonon interaction and the exciton phonon interaction have been determined. The obtained results indicate that the charge phonon coupling strengths are higher compared to the exciton phonon coupling.

Correlating Phase Behavior with Photophysical Properties in Mixed‐Cation Mixed‐Halide Perovskite Thin Films

“…[33,35,49] It has been proposed that the dominant mechanism for these broadening effects is Fröhlich coupling of photoexcited charge carriers with LO phonon modes. [50,51] We believe that these polaronic effects, originating from Fröhlich interactions between self-trapped electrons and phonon modes, are consistent with our observation of a Stokes shift which increases with temperature. Figure 3E plots the CW integrated PL emission intensity derived from Figure 3B.…”

Negative Thermal Quenching of Efficient White‐Light Emission in a 1D Ladder‐Like Organic/Inorganic Hybrid Material

“…Using a least‐square fit of Equation (3) to the experimental data, we obtain E op = 71 cm −1 , which is in the range of the PbBr 2 bending vibration modes thus indicating that the STE states are indeed located within the inorganic chains. It is well known that at low temperatures, acoustic phonon coupling dominates over optical phonon coupling in polar semiconductors . However, in our case, the value obtained for Γ ac is very low (10 −12 meV K −1 ) comparing to other homologous materials .…”

Colloidal Synthesis and Charge‐Carrier Dynamics of Cs2AgSb1−yBiyX6 (X: Br, Cl; 0 ≤y ≤1) Double Perovskite Nanocrystals

“…The PL narrows significantly from full width at half maximum (FWHM)=326 meV at 120 K down to 259 meV at 80 K (Insert of Figure S20). The charge carriers in perovskites can couple to both the longitudinal optical (LO) phonon (Fröhlich) and the acoustic phonons . From Raman measurements, the available phonon modes for LO phonon are located at 175 cm −1 (Figure S21).…”