Band‐Edge Exciton Fine Structure and Exciton Recombination Dynamics in Single Crystals of Layered Hybrid Perovskites

Abstract

2D perovskite materials have recently reattracted 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. Here, the band-edge exciton fine structure and in particular its exciton and biexciton dynamics in high quality crystals of (PEA) 2 PbI 4 are investigated. A comparison of bulk and surface exciton lifetimes yields a room temperature surface recombination velocity of 2 × 10 3 cm s −1 and an intrinsic lifetime of 185 ns. Biexciton emission is evidenced at room temperature, with a binding energy of ≈45 meV and a lifetime of 80 ps. 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 10 meV. This work contributes to the understanding of the complex scenario of the elementary photoexcitations in 2D perovskites. materials such as transition metal dichalcogenides, phosphorene, and graphene. They can be easily grown by both solution methods and vapor transport methods at low temperature, [14][15][16][17] with a tunable bulk direct bandgap. [18] These advantages make them appealing for future optoelectronic and photonic applications.Unlike their 3D counterparts, the dielectric and quantum confinement of carriers in the 2D perovskite layers gives rise to unusually strong excitonic effects. [19,20] It has been experimentally observed that excitons are tightly confined in the inorganic layers with binding energy as high as a few hundred millielectronvolts (significantly higher than that of 3D perovskites). [21] This greatly enhanced exciton binding energy makes them particularly interesting for light-emitting applications. [8,22] Moreover, 2D perovskites can exhibit a variety of multiexciton species, including biexcitons and trions. [20,23,24] The presence of these quasiparticles is exciting due to their unique role, leading to a better understanding of many body effects and their great promise for photonic applications. In addition, recent experiments reveal an important role of electron-phonon couplings on the exciton dynamics in 2D lead-iodide perovskite, suggesting a complex scenario for carrier relaxation and exciton formation. [25,26] It is therefore crucial to understand elementary photoexcitations in these layered materials. However, exciton fine structures and their properties are usually masked by local energy fluctuations resulting from disorder in thin films or broad emission due to the formation of self-trapped excitons. [27] Whereas their steady-state optical properties have

Brightening of dark excitons in 2D perovskites

“…Figure 4D shows the obtained bright-dark splitting as a function of the exciton binding energy [taken after (23,24,40)]. Extracted bright-dark splitting are about two times higher than recent estimations from temperature-dependent PL studies of (PEA) 2 PbI 4 or (PEA) 2 SnI 4 (32,34). The difference can stem from the fact that PL probes the lowest energy states, while absorption probes the highest density of states.…”

Influence of the Vibrational Modes from the Organic Moieties in 2D Lead Halides on Excitonic Recombination and Phase Transition

“…[ 1,2,17 ] Thus, 2D metal halides present a complex set of photophysical phenomena such as exciton–phonon coupling, [ 18,19 ] polaronic effects, [ 20–22 ] self‐trapped excitons (STEs), [ 2,23,24 ] broad band emission, [ 25–27 ] and dark excitonic states. [ 28,29 ]…”

Tuning Electronic Structure of 2D In2S3 via P Doping and Size Controlling Toward Efficient Photoelectrochemical Water Oxidation

“…These results reflect a decrease in radiative recombination under the help of In-P structure considering the fact that Auger recombination is negative. [40] To understand the surface chemical reaction after P doping, the charge oxidation kinetics η oxi represents the quantity of holes involved in the water oxidation (investigated by CIMPS). The increased η oxi of In 2 S 3 (s) describes an increase in hole injection efficiency, attributed to the more surface active sites are exposed due to the smaller size of nanosheets, significantly boosting the catalytic reactivity (Figure 6a).…”

“…These results reflect a decrease in radiative recombination under the help of In–P structure considering the fact that Auger recombination is negative. [ 40 ]…”