Single-Particle Spectroscopy as a Versatile Tool to Explore Lower-Dimensional Structures of Inorganic Perovskites

Abstract

The remarkable defect-tolerant nature of inorganic cesium halide perovskites, leading to near unity photoluminescence (PL) quantum yield and narrow emission line width across the entire visible spectrum, has provided a tantalizing platform for the development of a plethora of light-emitting applications. Recently, lower-dimensional (2D, 1D, and 0D) perovskites have attracted further attention due to their enhanced thermal, photo, and chemical stability as compared to their three-dimensional (3D) analogues. The combination of external size quantization and internal octahedral organization provides a unique opportunity to study and harness “multi-dimensional” electronic properties engineered on both atomic scale and nanoscale. However, crucial research to understand the elementary charge carrier dynamics in lower-dimensional perovskites lags far behind the enormous effort to incorporate them into optoelectronic devices. In this Perspective, we provide a review of recent developments that focus on studies of the dynamics of excitonic complexes in Cs-based perovskite nanocrystals using single-particle time-resolved PL spectroscopy and photon correlation measurements. Single-photon statistical studies not only offer an unprecedented level of detail to directly assess various recombination pathways, but also provide insights into specifics of the charge carriers' localization. We discuss the underlying physicochemical processes that govern PL emission and draw attention to a number of attributes within this class of the materials, especially lower-dimensional perovskites, that may indicate the common origin of the PL emission as well as provide a route map for the vast unexplored territories where single-particle spectroscopy can be a powerful tool to unravel crucial information.

Photoluminescence Blinking of Quantum Confined CsPbBr3 Perovskite Nanocrystals: Influence of Size

“…The cesium lead halide (CsPbX 3 , X= Cl, Br and I) perovskite nanocrystals (NCs) continue to receive great attention owing to their potential applications in optoelectronic devices such as in light-emitting diodes − and single-photon sources. − However, the fluctuation of photoluminescence (PL) of the single NCs of these substances between bright (on) and dark (off) states, ,,− and sometimes between the “on” and a low-intensity gray state, ,, is impediment to these applications. The PL fluctuation occurs over a rather broad timescale ranging from tens of microseconds to hundreds of seconds. , While the PL of these perovskite NCs originates from the radiative recombination of the electron and hole produced on photoexcitation, the fluctuation of PL is caused by the involvement of various trap states in these systems.…”

Highly Emissive Zero-Dimensional Cesium Lead Iodide Perovskite Nanocrystals with Thermally Activated Delayed Photoluminescence

“…Here, manipulation of the chemical synthesis with excessive A-site cations (Cs) leads to complete isolation of the octahedral units, improving the stability . While initial theoretical computations predicted 0D materials to be higher-bandgap and be nonluminescent, green-emissive (PLQY ∼ 100%) Cs 4 PbBr 6 single crystals and PNCs were soon demonstrated. − Despite initial suggestions that strong emission in these materials could be the result of small 3D (CsPbBr 3 ) inclusions, − various structural and optoelectronic characterizations ruled out this possibility and attributed the origin of the emission to the presence of molecular-like intrabandgap defects. ,− A number of experimental and theoretical studies pointed out that Br vacancies (V Br ) in 0D Cs 4 PbBr 6 have a low formation energy and can induce a midgap energy level appropriate to achieve the green emission. ,,− …”

Phase-Stable and Highly Luminescent CsPbI3 Perovskite Nanocrystals with Suppressed Photoluminescence Blinking

“…Among the cesium lead halide (CsPbX 3 with X = Cl, Br, and I) perovskite nanocrystals (NCs), the CsPbI 3 NCs, because of their low band gap, are the most promising candidates for solar photovoltaic and various optoelectronic applications. − However, poor phase stability of these NCs even under ambient condition is a major obstacle to these applications. − Apart from the stability-related issues, photoluminescence (PL) blinking of the single NCs is another factor that restricts the applications of the CsPbI 3 NCs as single-photon emitters and other light-emitting applications. − PL blinking is indeed an issue for all single emitters. Among different models invoked for explaining the PL blinking of semiconductor NCs, a charging model based on trapping of the carrier in long-lived trap states ,− and a multiple recombination center (MRC) model based on the trapping of the carrier in short-lived trap states ,− are the most common ones.…”