Interlayer Triplet-Sensitized Luminescence in Layered Two-Dimensional Hybrid Metal-Halide Perovskites

Abstract

Here we review an emerging class of 2D layered metal-halide perovskites that exhibit important photophysical behavior involving inorganic exciton-to-molecular triplet energy flow. These novel systems have potential to impact several energy-related fields and processes, including optoelectronics, photon upconversion strategies, and triplet-based photocatalysis. Early studies provided initial guidance and revealed several intriguing questions that more recent developments, in terms of both expanded and diversified compositional tuning and more sophisticated characterization, have begun to answer. These questions center around the delicate interplay between physical and electronic structure that is perturbed by choice of perovskite structural motif and organic spacer properties. In addition to their distinct natures, the energy offsets between the metal-halide and molecular excitons can be leveraged for a variety of unique effects and emergent properties, including fast interlayer energy transfer. We review the key advances with an eye toward strategies for controlling photophysical outcomes based on structure−energy−function relationships.

Two‐Dimensional Perovskites with Tunable Room‐Temperature Phosphorescence

“…Whereas the S 1 level of the organic spacer located above the E x prohibits the energy transfer from inorganic to organic components. [ 14 ] Once this energy transfer process occurs, the organic spacer rapidly relaxes to the minimum of potential energy surface of the triplet states, leading to a lower T 1 * excitation energy. The T 1 * excitation energy corresponds to the lowest emission peak of the phosphorescence, and it is an important design parameter for RTP materials.…”

“…If the triplet energy level of the organic spacers is located below the Wannier exciton level of the perovskite layer, the Dexter-type energy transfer from the inorganic layer to the organic layer may occur. [13,14] Once the energy transfer arises, subsequent recombination of the triplet excitons in the organic spacer layers can lead to the phosphorescence emission. This phenomenon was first reported by Era et al, who observed the strong phosphorescence of the organic spacer in the PbBr-based layer perovskites with naphthalene-linked ammonium molecules.…”

“…[15] Later, Ema et al proposed the Dexter-type energy transfer mechanism in 2D HOIPs, and this mechanism was confirmed by time-resolved photoluminescence measurements. [13] Despite a number of studies on designing 2D HOIP-based RTP materials have been reported in the literature, [11,14,[16][17][18][19] 2D HOIPs with highly efficient and persistent RTP are still very limited due in part to the huge unexplored chemical space and the lack of effective screen strategies. To date, most experimental studies on the search of highly efficient 2D HOIP-based RTP materials still employ the trial and error method.…”

Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal–Molecular Hybrids

“…The recent development of low-dimensional or two-dimensional (2D) halide perovskites offers an additional route to efficiently sensitize molecular triplets . 2D perovskites differ from their three-dimensional (3D) counterparts in that small A-site cations like methylammonium or cesium are replaced by bulky organic spacer cations, which separate the lead halide octahedra in the perovskite lattice. , 2D perovskites thus form an extended multiple quantum-well structure, with intimate contact between the sheets of inorganic lead halide octahedra and the organic cations.…”

“…However, movement of triplets within the 2D structure is challenging, and effective extraction of sensitized triplets is an important direction of ongoing research. Although the mechanistic understanding of triplet sensitization in 2D perovskite is still in a relatively nascent stage, it appears that triplet energy transfer proceeds via a Dexter-like two-step mechanism in naphthalene-containing 2D perovskites, − similar to that of perovskite nanocrystals. ,,, For further information on 2D perovskites for triplet sensitization, the interested reader is directed to recent reviews. , …”