[Paper Review] Band-edge Exciton Fine Structure and Exciton Recombination Dynamics in Single crystals of Layered Hybrid Perovskites

Hong‐Hua Fang, Jie Yang+7 more|arXiv (Cornell University)|Sep 25, 2019

Perovskite Materials and Applications1 references4 citations

TL;DR

This study investigates the band-edge exciton fine structure and recombination dynamics in high-quality single crystals of the layered hybrid perovskite (PEA)2PbI4 using transient photoluminescence and optical spectroscopy. It reveals a room-temperature intrinsic exciton lifetime of 185 ns, a surface recombination velocity of 2×10³ cm/s, and identifies a 10 meV bright/dark exciton splitting, with biexciton emission observed at 45 meV binding energy and 80 ps lifetime.

ABSTRACT

Two-dimensional (2D) perovskite materials have recently re-attracted intense research interest for applications in photovoltaics and optoelectronics. As a consequence of the dielectric and quantum confinement effect, they show strongly bound and stable excitons at room temperature. In this report, the band-edge exciton fine structure and in particular its exciton and biexciton dynamics in high quality crystals of (PEA)2PbI4 are investigated. A comparison of bulk and surface exciton lifetimes yields a room temperature surface recombination velocity of 2x10^3cm/s and an intrinsic lifetime of 185ns. Biexciton emission is evidenced at room temperature, with binding energy of about 45meV and a lifetime of 80ps. At low temperature, exciton state splitting is observed, which is caused by the electron-hole exchange interaction. Transient photoluminescence resolves the low-lying dark exciton state, with a bright/dark splitting energy estimated to be 10meV. This work contributes to understand the complex scenario of the elementary photoexcitations in 2D perovskites.

Motivation & Objective

• To understand the complex excitonic behavior in two-dimensional hybrid perovskites, particularly at the band edge.
• To resolve the fine structure of excitons, including bright and dark states, in high-quality single crystals.
• To quantify exciton recombination dynamics, distinguishing between bulk and surface contributions.
• To identify and characterize biexciton states at room temperature in layered perovskites.
• To determine the role of electron-hole exchange interaction in exciton splitting at low temperatures.

Proposed method

• Employed high-quality single crystals of (PEA)2PbI4 to minimize defects and enable precise measurements.
• Used transient photoluminescence spectroscopy to resolve exciton and biexciton recombination dynamics on picosecond timescales.
• Performed low-temperature optical measurements to observe exciton state splitting due to electron-hole exchange interaction.
• Extracted surface recombination velocity by comparing bulk and surface exciton lifetimes.
• Analyzed photoluminescence decay kinetics to estimate intrinsic exciton lifetime and bright/dark state splitting energy.
• Utilized supplementary material to support spectral analysis and data validation.

Experimental results

Research questions

• RQ1 What is the intrinsic exciton lifetime in (PEA)2PbI4 single crystals at room temperature?
• RQ2 How does surface recombination affect exciton dynamics, and what is the surface recombination velocity?
• RQ3 What is the energy splitting between bright and dark exciton states, and how is it influenced by electron-hole exchange interaction?
• RQ4 Can biexciton emission be observed at room temperature, and what are its binding energy and lifetime?
• RQ5 How do quantum and dielectric confinement effects manifest in the excitonic fine structure of 2D perovskites?

Key findings

• The intrinsic exciton lifetime in (PEA)2PbI4 single crystals at room temperature is 185 ns.
• The surface recombination velocity was determined to be 2×10³ cm/s, indicating moderate surface non-radiative losses.
• A bright/dark exciton splitting energy of 10 meV was observed at low temperature, attributed to electron-hole exchange interaction.
• Biexciton emission was confirmed at room temperature with a binding energy of approximately 45 meV and a lifetime of 80 ps.
• Low-lying dark exciton states were resolved via transient photoluminescence, confirming the presence of multiple excitonic states.
• The study demonstrates that strong excitonic effects persist at room temperature in 2D perovskites due to enhanced confinement and dielectric screening.