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Integrating second order nonlinear ( χ (2) ) optical materials on chip is an ongoing challenge for Si photonics. Noncentrosymmetric molecular crystals have the potential to deliver high χ (2) nonlinearity with good thermal stability, but so far have been limited to growth from solution or the melt, which are both difficult to control and scale up in manufacturing. Here, we show that large (>100 μm) single crystal domains of the nonlinear molecule 2-[3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene] malononitrile (OH1) can be grown monolithically on either glass or Si via vacuum evaporation, followed by a short thermal annealing step. The crystallites are tens of nanometer thick and exhibit strong second harmonic generation with their primary χ (2) tensor component lying predominantly in plane. Remarkably, we find that a single domain can grow uninterrupted through nearby channels etched on a Si wafer, which may provide a path to integrate OH1 on Si or Si3N4 waveguides for a broad range of χ (2) -based photonic integrated circuit functionality. [ABSTRACT FROM AUTHOR]

The preferential growth of α‐phase formamidinium perovskite (α‐FAPbI3) at low temperatures can be achieved with the incorporation of chloride‐based additives, with methylammonium chloride (MACl) being the most common example. However, compared to other less‐volatile chloride additives, MACl only remains in the growing perovskite film for a short time before evaporating during annealing, primarily influencing the early stages of film formation. In addition, evaporation of MACl as methylamine (MA0) and HCl can introduce a side reaction between MA0 and formamidinium (FA), undermining the compositional purity and phase stability of α‐FAPbI3. In this study, it is demonstrated that addition of iodine (I2) into the FAPbI3 precursor solution containing MACl suppresses the MA‐FA side reaction during annealing. Additionally, MACl evaporation is delayed owing to strong interaction with triiodide. The added I2 facilitates spontaneous growth of α‐FAPbI3 prior to annealing, with an improved bottom morphology due to the formation of fewer byproducts. Perovskite solar cells derived from an I2‐incorporated solution deliver a champion power conversion efficiency of 25.2% that is attributed to suppressed non‐radiative recombination. [ABSTRACT FROM AUTHOR]

2D Ruddlesden–Popper metal‐halide perovskites exhibit structural diversity due to a variety of choices of organic ligands. Incorporating bifunctional ligands in such materials is particularly intriguing since it can result in novel electronic properties and functions. However, an in‐depth understanding of the effects of bifunctional ligands on perovskite structures and, consequently, their electronic and excitonic properties, is still lacking. Here, n = 1 2D perovskites built with organic ligands containing ─CN, ─OH, ─COOH, ─phenyl (Ph), and ─CH3 functional groups are investigated using ultraviolet and inverse photoemission spectroscopies, density functional theory calculations, and tight‐binding model analyses. The experimentally determined electronic gaps of the ─CN, ─COOH, ─Ph, and ─CH3 based perovskites exhibit a strong correlation with the in‐plane Pb─I─Pb bond angle, while the ─OH based perovskite deviates from the linear trend. Based on the band structure calculations, this anomaly is attributed to the out‐of‐plane dispersion, caused predominantly by significant interlayer electronic coupling that is present in ─OH based perovskites. These results highlight the complex and diverse impacts of organic ligands on electronic properties, especially in terms of the involvement of strong interlayer electronic coupling. The impact of the bifunctional ligands on the evolution of the exciton binding energy is also addressed. [ABSTRACT FROM AUTHOR]

The ability to undergo spin-allowed exciton multiplication makes singlet fission materials promising for photovoltaic applications. Here, we examine the separation of correlated triplet pairs, (1)(T...T), in polycrystalline pentacene films via temperature-dependent transient absorption spectroscopy. Single wavelength analysis reveals a profound delay in [.sup.1](T...T) dynamics. Moreover, the dynamics of [.sup.1](T...T) exhibit temperature dependence, whereas other features show no discernable temperature dependence. Previous literatures have suggested that correlated triplet separation is mediated by a thermally activated hopping process. Surprisingly, we found that the time constants governing triplet pair separation display two distinct temperature-dependent regimes of triplet transport. The high temperature regime follows a thermally activated hopping mechanism. The experimentally derived reorganization energy and electronic coupling is verified by density matrix renormalization group quantum chemical calculations. In addition, we evaluated the low temperature regime and show that the trend can be modelled by a Miller-Abrahams-type model that incorporates the effects of energetic disorder. We conclude that the correlated triplet pair separation is mediated by thermally activated hopping or a disorder driven Miller-Abrahams-type mechanism at high and low temperature, respectively. We observe that crossover between two regimes occurs ~226 K. We find the time constant for triplet-triplet energy transfer to be 1.8 ps at ambient temperature and 21 ps at 77 K. Key words: pentacene, spin entanglement, disorder, thermal activation, Miller-Abrahams transport, Marcus theory. La capacite des excitons a subir une multiplication permise par le spin rend les materiaux a fission d'excitons singulet prometteurs dans le contexte d'applications en photovoltaique. Dans le cadre des presents travaux, nous avons examine la separation des paires triplet correlees [.sup.1](T...T) dans des films de pentacene polycristallin par spectroscopie d'absorption transitoire dependante de la temperature. L'analyse a differentes longueurs d'onde a montre un delai considerable dans la dynamique des paires [.sup.1](T... T). Par ailleurs, cette dynamique des paires [.sup.1](T... T) s'est revelee dependante de la temperature, alors que d'autres caracteristiques ne montrent aucune dependance notable en fonction de la temperature. Des publications anterieures ont avance l'hypothese que la separation de paires triplet correlees s'effectue par un processus de saut active thermiquement. Etonnamment, nous avons constate que les constantes temporelles regissant la separation des paires triplet montrent deux regimes distincts de transport de triplets dependants de la temperature. Le regime a haute temperature suit un mecanisme de saut active thermiquement. L'energie de reorganisation et le couplage electronique derives experimentalement ont ete verifies par calculs de chimie quantique sur le groupe de normalisation de la matrice densite. De plus, nous avons evalue le regime a basse temperature et nous avons montre que la tendance pouvait etre modelisee selon un modele de type Miller-Abrahams qui tient compte des effets du desordre energetique. Nous avons conclu que la separation de paires triplet correlees procede selon un saut active thermiquement a haute temperature ou selon un mecanisme de type Miller-Abrahams gouverne par le desordre a basse temperature. Par ailleurs, nous avons observe que le croisement entre les deux regimes se produit autour de 226 K. Nos resultats montrent que la constante temporelle du transfert d'energie triplet-triplet est de 1,8 ps a temperature ambiante et de 21 ps a 77 K. [Traduit par la Redaction] Mots-cles: pentacene, enchevetrement de spins, desordre, activation thermique, transport Miller-Abrahams, theorie de Marcus., Introduction Triplet excitons have been demonstrated to play a key role in numerous photochemical processes including thermally activated delayed fluorescence (TADF), triplet--triplet annihilation (TTA), and singlet fission. Utilizing triplet excitons [...]

An organic diode is demonstrated that near‐field energy transfers to molecules in solution via surface plasmon polaritons, in contrast to typical far‐field excitation via absorption of traveling photons. Electrically generated excitons couple to surface plasmon modes in the cathode; the plasmons subsequently excite chromophore molecules on top of the cathode. External quantum efficiency and time resolved photoluminescence measurements are used to characterize the diode and the near‐field energy transfer process. In addition, it is shown that excited chromophores can charge‐transfer to quencher molecules, illustrating the potential of this device to be used for photochemical applications. [ABSTRACT FROM AUTHOR]