Abstract
Self-assembled hybrid perovskite quantum wells have attracted attention due to their tunable emission properties, ease of fabrication, and device integration. However, the dynamics of excitons in these materials, especially how they couple to phonons, remains an open question. Here, we investigate two widely used materials, namely, butylammonium lead iodide (CH3(CH2)3NH3)2PbI4 and hexylammonium lead iodide (CH3(CH2)5NH3)2PbI4, both of which exhibit broad photoluminescence tails at room temperature. We performed femtosecond vibrational spectroscopy to obtain a real-time picture of the exciton-phonon interaction and directly identified the vibrational modes that couple to excitons. We show that the choice of the organic cation controls which vibrational modes the exciton couples to. In butylammonium lead iodide, excitons dominantly couple to a 100 cm-1 phonon mode, whereas in hexylammonium lead iodide, excitons interact with phonons with frequencies of 88 and 137 cm-1. Using the determined optical phonon energies, we analyzed photoluminescence broadening mechanisms. At low temperatures (<100 K), the broadening is due to acoustic phonon scattering, whereas at high temperatures, LO phonon-exciton coupling is the dominant mechanism. Our results help explain the broad photoluminescence line shape observed in hybrid perovskite quantum wells and provide insights into the mechanism of exciton-phonon coupling in these materials.
Highlights
Organometal halide hybrid perovskites have become one of the most promising materials for highly efficient and low-cost optoelectronic devices
At low temperatures (
We performed femtosecond transient absorption spectroscopy to obtain a real-time picture of how excitons couple to phonons and directly identified the phonon modes that couple to excitons
Summary
Organometal halide hybrid perovskites have become one of the most promising materials for highly efficient and low-cost optoelectronic devices. Due to the hydrophobic property of organic cations, 2D perovskite devices retain their performance under ambient humidity levels.2 2D perovskites have been successfully implemented into solar cell[2−4] and light-emitting device (LED) fabrication.[5] Because quantum-confined excitons result in efficient radiative decay, the LEDs exhibit high external quantum efficiency of up to 11.7%.6. These encouraging studies show that hybrid perovskite quantum wells can be a promising candidate for the fabrication of efficient and long-term stable devices. We show that in 2D perovskites, the coupling strength between LO phonons and excitons is several tens of meV
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