Control over the Vertical Growth of Single Calcitic Crystals in Biomineralized Structures

Acidic biomacromolecules frequently incorporate into biomineralized structures to control the morphology and extent of crystal growth. The study of such processes has been hindered by the scarcity of a model system that mimics the influence of acidic biomacromolecules on mineral crystal growth. A carbonic anhydrase-assisted system was developed to model CaCO3 deposition at an air/solution interface. Textured CaCO3 crystals were found to grow in a direction orthogonal (vertical) to the air/solution interface. The crystal growth anisotropy became more pronounced upon addition of an anionic polymer, and an amorphous morphology was found at sufficiently high polymer concentrations. X-ray diffraction and high-resolution transmission electron microscopy studies showed that most calcite crystals grew along the (01̅4) and (001) planes vertically, whereas the (012) and (110) planes were oriented in the lateral direction. The added acidic polymers adsorbed predominantly onto the (012) or (110) faces of the growing crystals, contributing to epitaxy and crystal growth anisotropy in the vertical direction by inhibiting crystal growth at specific lateral faces that interacted with the acidic polymer. This alignment is characteristic of crystal growth in biomineralized calcites. These observations suggest that the presence of the acidic biomacromolecules induce crystals to grow with specific longitudinal and lateral orientations

Dependence of Exciton Diffusion Length on Crystalline Order in Conjugated Polymers

Exciton diffusion in organic semiconductors is crucial to the performance of organic solar cells. Here, we measured the exciton diffusion length in poly­(3-hexylthiophene) (P3HT) as a function of the crystalline order using spectrally resolved photoluminescence quenching (SR-PLQ) techniques. The crystalline order in the P3HT films, characterized according to the mean crystal size and normalized crystallinity, was varied by changes in thermal treatment temperatures. The exciton diffusion length increased from 3 to 7 nm as the mean crystal size increased more than twice and the crystallinity increased by a factor of 6. A higher crystalline order improved the spectral overlap and reduced the distance between chromophores, enhancing Förster-mediated exciton diffusion. The higher crystalline order also lengthened the conjugated segments and reduced the energetic disorder, producing favorable condition for exciton hopping

Improved Thermal Stability and Operational Lifetime of Blue Fluorescent Organic Light-Emitting Diodes by Using a Mixed-Electron Transporting Layer

Since the chemical and thermal stability of organic thin film layers in organic light-emitting diodes (OLEDs) highly influences the operational device lifetime, a rational advanced design of materials and device structures is quite necessary. Here, we report a significant improvement in the device thermal stability and operational lifetime of blue-fluorescent OLEDs by adopting a mixed electron transporting layer (mETL) of 4,7-diphenyl-1,10-phenanthroline (BPhen) and hydroxyquinolinolato-lithium (Liq). Compared to pristine BPhen film, Liq mixing improved thermal and morphological stabilities of the mETL by increasing the glass-transition temperature and inhibiting crystallization of the ETL, which directly leads to better device performances. Compared to the reference device using the pristine BPhen film as an ETL, the device with mETL containing 50% Liq maintains the device characteristics, with respect to the thermal stress up to 110 °C, which is a 60 °C increase in the thermal stability of the blue device by applying mETL. Accordingly, the operational lifetime of the device with mETL containing 50% Liq is substantially extended by 67 times, ensuring that this remarkable device lifetime enhancement is dominantly driven by the improved thermal and morphological stabilities of mETL

Boosting Photon Harvesting in Organic Solar Cells with Highly Oriented Molecular Crystals <i>via</i> Graphene–Organic Heterointerface

Photon harvesting in organic solar cells is highly dependent on the anisotropic nature of the optoelectronic properties of photoactive materials. Here, we demonstrate an efficient approach to dramatically enhance photon harvesting in planar heterojunction solar cells by using a graphene–organic heterointerface. A large area, residue-free monolayer graphene is inserted at anode interface to serve as an atomically thin epitaxial template for growing highly orientated pentacene crystals with lying-down orientation. This anisotropic orientation enhances the overall optoelectronic properties, including light absorption, charge carrier lifetime, interfacial energetics, and especially the exciton diffusion length. Spectroscopic and crystallographic analysis reveal that the lying-down orientation persists until a thickness of 110 nm, which, along with increased exciton diffusion length up to nearly 100 nm, allows the device optimum thickness to be doubled to yield significantly enhanced light absorption within the photoactive layers. The resultant photovoltaic performance shows simultaneous increment in <i>V</i>_oc, <i>J</i>_sc, and FF, and consequently a 5 times increment in the maximum power conversion efficiency than the equivalent devices without a graphene layer. The present findings indicate that controlling organic–graphene heterointerface could provide a design strategy of organic solar cell architecture for boosting photon harvesting

Molecular Design of Deep Blue Thermally Activated Delayed Fluorescence Materials Employing a Homoconjugative Triptycene Scaffold and Dihedral Angle Tuning

Molecular Design of Deep Blue Thermally Activated Delayed Fluorescence Materials Employing a Homoconjugative Triptycene Scaffold and Dihedral Angle Tunin