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Low-dimensional copper halides having nontoxic elements are attracting increasing attention for their peculiar emission properties. Self-trapped excitons (STEs) account for their high photoluminescence quantum yields (PLQYs) with emission that can stretch across the entire visible spectrum. However, intrinsic factors that influence the formation or loss of the emissive species in low-dimensional copper halides remain elusive. Here, a comprehensive study on the STE formation dynamics of one-dimensional CsCu 2 I 3 and zero-dimensional Cs 3 Cu 2 I 5 is presented. It is found from STE kinetic analysis that a slower STE formation demonstrated by the 1D structure is not hindered by a potential barrier, but instead related to the number of phonons released in the self-trapping process. It is further revealed that in 1D CsCu 2 I 3 , the non-radiative recombination of STEs mainly occurs via the intersection between the STE state and the ground state in the configuration coordinate diagram, placing an intrinsic limit on the PLQY at room temperature. These findings show that the STE formation is affected by both the self-trapping depth and the phonon energy as opposed to a potential barrier in low-dimensional copper halides. The better understanding of STE formation and recombination processes provide basis for improving design and performance for broadband light emitting devices.

Energy losses significantly reduce the open-circuit voltage among current state-of-the-art organic solar cells (OSCs), which limits the further enhancement of their power conversion efficiencies (PCEs). In this study, the bulk heterojunction blends of PM6 donor and halogenated nonfullerene acceptors (NFAs) display a trade-off between radiative energy losses, i.e., charge transfer state (CTS) radiative energy loss (ΔE rad ) and the loss associated with CTS formation from acceptor singlet excitons (ΔE CT EL ). Similarly, a trade-off between ΔE rad and the nonradiative energy loss (ΔE nr ) is found, reflecting a competition in radiative and nonradiative charge recombination pathways. Further, the energy levels of relaxed CTS (E CT EL ) are shown to exhibit dependence on morphologically induced energetic traps, suggesting that it should not be associated merely to blend constituents. Interestingly, these correlations extend even to thermally degraded devices considered herein. Accordingly, this work provides further understandings of energy losses relevant to overcome the current limitations concerning NFA-based OSC developments.

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Ternary copper halides are promising materials for lighting and displays, but red emission has yet to be reported among this class of materials due to the difficulty in tuning the self-trapped exciton (STE) emission. Here, we report lead-free hybrid organic−inorganic ternary copper halides A 6 (DMSO) 12 [Cu 8 Br 13 ][Cu 4 Br 4 (OH)(H 2 O)] (ACB-DMSO, A = K, Rb) synthesized as single crystals and microcrystalline suspensions. These materials emit in the red portion of the visible spectrum with a high photoluminescence quantum yield (PLQY) of up to 75%. The changes in the emission spectrum are caused by the solvent-induced transformation from the STE emitter A 2 CuBr 3 to phosphorescent ACB-DMSO which reversibly transforms blue-emitting 1D copper chains to red-emitting 0D copper clusters. K 6 (DMSO) 12 [Cu 8 Br 13 ][Cu 4 Br 4 (OH)(H 2 O)] (A = K) can be used as the red-emitting phosphor for red light-emitting didoes (LEDs), and by adding blue and green emitting cesium copper halides, an all copper-based white LED with a high color rendering index (CRI) over 97% is achieved.

Ternary copper halides have garnered significant interest for their bright, high quantum yield emission stemming from the radiative decay of self‐trapped excitons (STEs). Cesium copper halides have shown promise for use in optoelectronics, including light‐emitting devices (LEDs) for lighting and displays. To date several synthetic procedures for Cs3Cu2X5 (X = Cl, Br, and mixed Br/Cl) have been proposed for making nanocrystals, microcrystals, or polycrystalline thin films. Here, a synthetic method for making large single crystals (SCs) with millimeter dimensions in less than 30 min is presented. Phase pure mixed halide SCs are also produced and in‐depth structural analysis has been performed for the first time, definitively showing the site preferences for mixing chloride into the pure Cs3Cu2Br5 structure. Quantum yields for SCs of X = Cl and Br are 100% and 27% respectively, with long lifetimes and strong evidence of STE emission. This synthesis can be used to produce white light UV‐downconversion LEDs using ternary copper halides as the blue and green components along with the commercial red phosphor K2SiF6:Mn4+. These devices give a Commission Internationale de l'Éclairage (CIE) coordinate of (0.3327, 0.3342) and color rendering index of 90% at a color temperature of ≈5500 K.

Transient optical spectroscopy is used to quantify the temperature-dependence of charge separation and recombination dynamics in P3TEA:SF-PDI 2 and PM6:Y6, two non-fullerene organic photovoltaic (OPV) systems with a negligible driving force and high photocurrent quantum yields. By tracking the intensity of the transient electroabsorption response that arises upon interfacial charge separation in P3TEA:SF-PDI 2 , a free charge generation rate constant of ≈2.4 × 10 10 s −1 is observed at room temperature, with an average energy of ≈230 meV stored between the interfacial charge pairs. Thermally activated charge separation is also observed in PM6:Y6, and a faster charge separation rate of ≈5.5 × 10 10 s −1 is estimated at room temperature, which is consistent with the higher device efficiency. When both blends are cooled down to cryogenic temperature, the reduced charge separation rate leads to increasing charge recombination either directly at the donor-acceptor interface or via the emissive singlet exciton state. A kinetic model is used to rationalize the results, showing that although photogenerated charges have to overcome a significant Coulomb potential to generate free carriers, OPV blends can achieve high photocurrent generation yields given that the thermal dissociation rate of charges outcompetes the recombination rate.