Unveiling the Intrinsic Photophysics in Quasi-Two-Dimensional Perovskites

Abstract

The two-dimensional (2D) perovskites have drawn intensive attention due to their unique stability and outstanding optoelectronic properties. However, the debate surrounding the spatial phase distribution and band alignment among different 2D phases in the quasi-2D perovskite has created complexities in understanding the carrier dynamics, hindering material and device development. In this study, we employed highly sensitive transient absorption spectroscopy to investigate the carrier dynamics of (BA)2(MA) n−1Pb n I3n+1 quasi-2D Ruddlesden–Popper perovskite thin films, nominally prepared as n = 4. We observed the carrier-density-dependent electron and hole transfer dynamics between the 2D and three-dimensional (3D) phases. Under a low carrier density within the linear response range, we successfully resolved three ultrafast processes of both electron and hole transfers, spanning from hundreds of femtoseconds to several picoseconds, tens to hundreds of picoseconds, and hundreds of picoseconds to several nanoseconds, which can be attributed to lateral-epitaxial, partial-epitaxial, and disordered-interface heterostructures between 2D and 3D phases. By considering the interplay among the phase structure, band alignment, and carrier dynamics, we have proposed material synthesis strategies aimed at enhancing the carrier transport. Our results not only provide deep insights into an accurate intrinsic photophysics of quasi-2D perovskites but also inspire advancements in the practical application of these materials.

Characterization of Intrinsic Charge Carrier Dynamics in Lead Halide Perovskite Films Using Time-Resolved Terahertz Spectroscopy

“…The diffusion process of charge carriers within lead halide perovskite semiconductors is critical for defining the performance of optoelectronic devices like solar cells and light-emitting diodes. − The determination of the carrier diffusion length ( L D ) in perovskite films has been extensively investigated using various techniques, including photoluminescence quenching, , transient absorption microscopy, − terahertz, and microwave conductivity. − However, the measured values of L D exhibit significant variations depending on the employed measurement methods, ranging from approximately 0.1 to 10 μm . Essentially, L D is influenced by the carrier diffusion coefficient (D) and carrier lifetime (τ), with the relationship L D = D τ .…”

Effects of the Phase Spatial Distribution on the Intrinsic Carrier Dynamics in Quasi-2D Perovskite Films

“…Recently, Yu et al. and our group both reported that quasi-2D perovskite thin films were composed of the randomly distributed 2D (small- n ) phases in the matrix of the 3D ( n = ∞) perovskite phase, where 2D phases block the electron transport and even serve as hole traps under illumination, observed by transition absorption spectroscopy (TAS) . All investigations show that the phase distribution directly affects the carrier dynamics in quasi-2D perovskite films.…”

“…In summary, the relationship between the phase spatial distribution and carrier dynamics under working conditions is schematically illustrated in Figure e. The F0 film with 2D/3D bulk heterojunction can be treated as a large number of potential wells, which hinder electron transport in the 3D phase and trap holes in the 2D phase . The F3 film with 3D (MAPbI 3 )/2D-3D mixed phase planar heterojunction distribution contains fewer potential wells in the front side, which allows efficient electron transport in the 3D phase and avoids the trapping of holes in 2D phases.…”

Pressure-Induced Changes in the Phase Distribution and Carrier Dynamics of Quasi-Two-Dimensional Ruddlesden–Popper Perovskites

“…Despite being nominally prepared using a single n , the resulting products consist of different numbers of phases centered around n leading to the formation of energy funnels. High-sensitivity transient absorption (TA) spectroscopy studies of their carrier dynamics can reveal ground-state bleach signals from different phases and electron–hole transport dynamics correlated with carrier density across these phases, ,,,, but systematic investigations of the absorption and emission mechanisms, phase distributions, and their correlation with carrier dynamics in quasi-2D RP perovskites are still needed to advance their applications in light conversion and light-emitting devices. To delve deeper into the interactions between their structures, an effective tuning knob is required that can adjust the material’s structure and electronic properties without altering its composition. , …”