Colloidally stable suspensions of lead halide perovskite nanocrystals are prepared from high-quality lead halide nanocrystal seeds. Perovskite nanocrystals with different layered crystal structures are reported. These systems are well suited for investigations of the intrinsic photophysics and spectroscopy of organic-inorganic metal halide perovskites.
The conversion of photoexcitations into charge carriers in organic solar cells is facilitated by the dissociation of excitons at the donor/acceptor interface. The ultrafast timescale of charge separation demands sophisticated theoretical models and raises questions about the role of coherence in the charge-transfer mechanism. Here, we apply two-dimensional electronic spectroscopy to study the electron transfer process in poly(3-hexylthiophene)/PCBM (P3HT/PCBM) blends. We report dynamics maps showing the pathways of charge transfer that clearly expose the significance of hot electron transfer. During this ultrafast electron transfer, vibrational coherence is directly transferred from the P3HT exciton to the P3HT hole polaron in the crystalline domain. This result reveals that the exciton converts to a hole with a similar spatial extent on a timescale far exceeding other photophysical dynamics including vibrational relaxation.
Hierarchical, three-fold symmetrical, single-crystalline gold dendrites were synthesized by the reaction between a zinc plate and a solution of HAuCl 4 in the ionic liquid [BMIM][PF 6 ]. The unique dendritic gold nanostructures show a three-order hierarchy (i.e., a three-fold symmetrical <111>-oriented trunk, three groups of trident-like <111>-oriented branches grown on the trunk, and many <111>-oriented nanorod leaves grown on the branches symmetrically), indicating an interesting fractal growth. According to the investigation on the growth process of the gold dendrites, it was proposed that gold nuclei nanocrystals first formed on the zinc substrate through a direct surface reaction and that the subsequent crystal growth preferentially took place on the preformed gold crystals through a primary cell reaction, leading to the formation of the final hyperbranched dendrites under nonequilibrium conditions. In contrast, AuZn alloy dendrites consisting of aggregated primary nanoparticles were produced when the ionic liquid solution was replaced by an aqueous solution. It was proposed that the significantly lowered ion diffusivity and reaction rate in the ionic liquid medium could largely contribute to the formation of the pure singlecrystalline gold dendrites. Moreover, electrocatalytic measurements performed in alkaline solution suggested that the obtained dendritic gold nanostructures exhibited good electrocatalytic activity toward the oxidation of methanol, which might be related to the special three-order hierarchical architectures.
The origin and yield of charges in neat conjugated polymers has long been controversial. In this paper, we review the body of literature that has been created over the past three decades of research in this field and provide insight from our own recent work highlighting the importance of polymer microstructure in understanding the photophysics of these materials. We focus primarily on polythiophene, poly(p-phenylene vinylene), and ladder-type poly(p-phenylene) derivatives, as these three prototypical polymer backbone structures have undergone the most complete study. We find compelling evidence that the primary photoexcitations in conjugated polymers include both intrachain excitons and excimers, that charges are produced in a secondary process, primarily from breakup of intrachain excitons, and that the locus of long-lived charge generation is at the interface between amorphous and crystalline domains of the polymer. Interestingly, the existence of interchromophore complexes that we refer to as excimers has largely been ignored in the development of organic photovoltaics based on conjugated polymers. We suggest that the prevalence of this species may help explain certain mysterious features in that body of work, in particular the excess energy offset required for efficient charge separation in donor/acceptor blends and the requirement for intimately mixed phases of the two materials for maximally efficient photocurrent generation.
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