Emissive State Dynamics of Quasi-2D Lead Halide Perovskite Single Crystals

Abstract

Quasi-two-dimensional (quasi-2D) metal halide perovskites (MHPs) are important low-dimensional semiconductor systems because of their strong excitonic response, tunable emission properties, and improved structural stability compared with conventional three-dimensional (3D) perovskites. In these materials, the inorganic layer thickness and the molecular structure of the organic spacer can modulate quantum confinement, exciton localization, and excited-state relaxation pathways. Understanding these structure-dependent photophysical processes is therefore important for the rational design of perovskite-based optoelectronic materials.

This thesis investigates the emissive-state dynamics of quasi-2D lead halide perovskite single crystals, various quantum well thickness n-pentylammonium lead bromide (n-PAPB)(n=1), n-PAPB(n=2), as well as the organic spacer n-PAPB(n=2), n-butylammonium methylammonium lead bromide (n-BAPB)(n=2), and iso-butylammonium methylammonium lead bromide (iso-BAPB)(n=2)). Steady-state absorption spectroscopy, photoluminescence (PL) spectroscopy, temperature-dependent PL spectroscopy, time-resolved photoluminescence (TRPL), and transient absorption (TA) spectroscopy were used to examine their optical properties and excited-state dynamics.

The absorption and PL spectra suggest the coexistence of multiple quasi-2D domains, likely dominated by n=1-3 phases. Excitation intensity-dependent PL measurements show nearly linear intensity scaling with excitation power, which can be attributed to the dominated excitonic radiative recombination under the investigated excitation conditions. Temperature-dependent PL measurements reveal pronounced electron-phonon interactions that influence the charge carrier recombination at the emissive states. The extracted exciton binding energies are approximately 84-110 meV, indicating strongly localized excitonic states in these quasi-2D structures. Linewidth broadening analysis further suggests coupling between excitons and longitudinal optical phonons. TA spectroscopy indicates ultrafast charge carrier relaxation followed by the formation of long-lived localized excited states.

Overall, this work shows that both inorganic layer thickness and spacer molecular structure are closely correlated with the excited-state dynamics of quasi-2D perovskites. The results provide insight into structure-dependent exciton localization, carrier-phonon interactions, and emissive-state relaxation processes in layered perovskite systems.

Keywords: quasi-2D perovskites; lead halide perovskites; photoluminescence; transient absorption; electron-phonon coupling.

Popular Abstract

Efficient light-emitting and light-absorbing materials are essential for modern optoelectronic technologies, including solar cells, LEDs, lasers, and photodetectors. Metal halide perovskites have attracted broad interest because their optical properties can be tuned by changing their chemical composition and crystal structure.

This thesis focuses on quasi-two-dimensional (quasi-2D) perovskites. In these materials, thin inorganic layers are separated by organic molecules, forming structures that resemble natural quantum wells. This layered arrangement confines electrons and holes within the inorganic regions and gives rise to strong light-emission properties.

The aim of this work was to understand how the thickness of the inorganic layers and the structure of the organic molecules affect light emission in quasi-2D perovskite single crystals. Several crystals were studied using optical spectroscopy methods, including steady-state and time-resolved measurements. These techniques make it possible to follow how excited carriers and excitons relax after light absorption.

The results show that the investigated crystals exhibit strong excitonic emission and clear interactions between excited carriers and lattice vibrations. The emission behavior depends on both the inorganic layer thickness and the organic spacer structure. In particular, the branched organic spacer leads to broader and red-shifted emission, suggesting stronger lattice distortion and enhanced exciton localization.

Ultrafast transient absorption measurements further show that photoexcited carriers relax rapidly after excitation and can form long-lived localized excited states. These processes are closely related to carrier-phonon interactions and local structural distortion in the quasi-2D lattice.

Overall, this thesis improves the understanding of how structural factors control light-emission processes in quasi-2D perovskites. Such knowledge may help guide the design of perovskite materials with improved emission properties and stability.

• author: Gu, Chenyang
• supervisor: Kaibo Zheng
• organization: Department of Physics; Chemical Physics
• course: PHYM03 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry; Physics and Astronomy
• language: English
• id: 9250175
• date added to LUP: 2026-09-07 14:13:20
• date last changed: 2026-09-07 14:13:20