Triplet Sensitization by “Self-Trapped” Excitons of Nontoxic CuInS₂ Nanocrystals for Efficient Photon Upconversion

Abstract

Triplet energy transfer (TET) from semiconductor nanocrystals (NCs) has recently emerged as a new triplet sensitization paradigm. It remains unclear how trap states pervasive in NCs influence TET or whether trapped excitons can undergo efficient TET. Here we partially address this issue by studying TET from CuInS 2 NCs as a model system because their photogenerated excitons are known to be "self-trapped" due to hole localization to intragap Cu states. We found that, thanks to the long lifetime (209 ± 17 ns) of self-trapped excitons, they could be extracted with an efficiency of ∼92.3% by surface-anchored anthracene despite that the TET rate was relatively slow (57.1 ± 1.7 μs −1 ). We further leveraged this efficient sensitization to achieve triplet− triplet-annihilation photon upconversion (TTA-UC) with a quantum yield of 18.6 ± 0.3%. Thus, this study not only demonstrates trapped excitons can undergo efficient TET as well, but also presents the first TTA-UC system sensitized by nontoxic NCs which is important for the real-life application of this technique.

One‐Step Fabrication of Perovskite‐Based Upconversion Devices

“…A wide variety of materials classes for use as triplet sensitizers have been reported, ranging from metal-organic complexes with strong spin-orbit coupling, [4,19,20,22,[26][27][28][29][30][31] conventional semiconductor quantum dots (QDs)" [32][33][34][35][36][37][38][39][40] two-dimensional CdSe nanoplatelets, [41] perovskite-based QDs, [17,21,42,43] transition metal dichalcogenides, [44,45] two-dimensional perovskites [46] to bulk three-dimensional perovskites. [47][48][49][50][51] In the following, we will focus on the methylammonium formamidinium lead triiodide (MAFA) bulk perovskite sensitization of triplet states in the organic semiconductor rubrene by charge transfer.…”

Blue Light Emitting Defective Nanocrystals Composed of Earth‐Abundant Elements

“…Copper‐based ternary chalcogenide NCs are low‐toxicity alternatives to Cd‐ and Pb‐based quantum dots, both of which have been widely studied for photon down‐conversion, photon up‐conversion, luminescent solar concentrators (LSCs), solar cells, light‐emitting diodes, and bio‐imaging . Over the past two decades, Cu‐In‐S ternary NCs have been synthetically optimized and commercialized .…”

Mechanisms of triplet energy transfer across the inorganic nanocrystal/organic molecule interface

“…For example, researchers have pursued the ideas of harvesting the SF-induced triplets of polycyclic aromatic hydrocarbons (PAHs) such as tetracene and pentacene using either silicon solar cells 12,13 or lead chalcogenide nanocrystals (NCs) 7,8,14 for efficiency-doubled light conversion or emission. Alternatively, inorganic semiconductors, and in particular their NCs, can be used to sensitize the triplets of PAHs for TTA-UC 9,[15][16][17][18][19] . The advantage of these inorganic sensitizers over traditional molecular sensitizers lies in the much weaker bright-dark states splitting (a few to 10 s of meV) in inorganic semiconductors compared with molecules (100 s of meV) allowing for a higher upconversion energy gain 20,21 .…”