Momentarily trapped exciton polaron in two-dimensional lead halide perovskites

Abstract

Two-dimensional (2D) lead halide perovskites with distinct excitonic feature have shown exciting potential for optoelectronic applications. Compared to their three-dimensional counterparts with large polaron character, how the interplay between long- and short- range exciton-phonon interaction due to polar and soft lattice define the excitons in 2D perovskites is yet to be revealed. Here, we seek to understand the nature of excitons in 2D CsPbBr3 perovskites by static and time-resolved spectroscopy which is further rationalized with Urbach-Martienssen rule. We show quantitatively an intermediate exciton-phonon coupling in 2D CsPbBr3 where exciton polarons are momentarily self-trapped by lattice vibrations. The 0.25 ps ultrafast interconversion between free and self-trapped exciton polaron with a barrier of ~ 34 meV gives rise to intrinsic asymmetric photoluminescence with a low energy tail at room temperature. This study reveals a complex and dynamic picture of exciton polarons in 2D perovskites and emphasizes the importance to regulate exciton-phonon coupling.

Correlated Dynamics of Free and Self‐Trapped Excitons and Broadband Photodetection in BEA2PbBr4 Layered Crystals

“…A similar phenomenon has been observed in anthracene and few‐layer CsPbBr 3 . [ 8,31 ] However, E trap is much larger than E detrap in those two cases, [ 8,31 ] and consequently, STEs are metastable and can only be observed at high temperatures. For STEs reported in other 2D LHPs, E trap is generally much smaller than E detrap , leading to a minor detrapping efficiency.…”

“…The underlying mechanisms of such ultrafast processes are complicated and strongly depend on the lattice temperature, energy barriers (defined by the exciton–phonon coupling strength), sample quality, and so on. [ 8,19,21,22 ] For certain types of perovskites, the fluorescence shows nonexponential decay, indicating a dynamic dephasing process between free exciton states and self‐trapped states. [ 16,21,23 ] However, the physical mechanism of this phenomenon remains unsolved.…”

“…The underlying mechanisms of such ultrafast processes are complicated and strongly depend on the lattice temperature, energy barriers (defined by the exciton-phonon coupling strength), sample quality, and so on. [8,19,21,22] For certain types of perovskites, the fluorescence shows nonexponential decay, indicating a dynamic dephasing process between free exciton states and self-trapped Self-trapped excitons (STEs) exert a profound impact on the optical properties and device applications of 2D halide perovskites. Particularly distinct exciton self-trapping and detrapping processes can facilitate the intelligent design of perovskite optoelectronic devices with emerging functionalities.…”

Stabilization of Metastable Halide Perovskite Lattices in the 2D Limit

“…The main peak arises from free exciton emission, while the lower energy tail is attributed to localized exciton emission due to strong exciton‐phonon coupling. [ 94 ] Interestingly, it was found that the higher spectral asymmetry with increasing the A‐cation size is correlated with the PL quenching (Table 1). This correlation emphasizes the importance of exciton phonon interaction in determining the PL properties.…”

Interfacial transport modulation by intrinsic potential difference of janus TMDs based on CsPbI3/J-TMDs heterojunctions

“…In recent years, lead halide perovskites have attracted great attention in the application of high-performance photovoltaic and optoelectronic because of their large optical absorption coefficient, low cost, simple preparation, etc. ( Gu et al., 2020 ; Guzelturk et al., 2021 ; Tao et al., 2021 , 2020 ; Wang et al., 2021a ; Wang et al., 2020 ) Photodetectors based on lead halide perovskites have been widely applied in diverse fields including optical communication, remote sensing, military surveillance, imaging technology, and industry automation control. However, it should be noted that the organic-inorganic lead halide perovskite possesses the poor stability which hinders the development of perovskite devices ( Li et al., 2019 ; Zhou and Zhao, 2019 ).…”