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Low-dimensional perovskites attract increasing interest due to tunable optoelectronic properties and high stability. Here, it is shown that perovskite thin films with a vertical gradient in dimensionality result in graded electronic bandgap structures that are ideal for photodiode applications. Positioning low-dimensional, vertically-oriented perovskite phases at the interface with the electron blocking layer increases the activation energy for thermal charge generation and thereby effectively lowers the dark current density to a record-low value of 5 × 10−9 mA cm−2 without compromising responsivity, resulting in a noise-current-based specific detectivity exceeding 7 × 1012 Jones at 600 nm. These multidimensional perovskite photodiodes show promising air stability and a dynamic range over ten orders of magnitude, and thus represent a new generation of high-performance low-cost photodiodes.

(Figure Presented) Controlling the morphology of soluble small molecule organic semiconductors is crucial for the application of such materials in electronic devices. Using a simple dip-coating process we systematically vary the film drying speed to produce a range of morphologies, including oriented needle-like crystals. Structural characterization as well as electrical transistor measurements show that intermediate drying velocities produce the most uniformly aligned films. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.

The anisotropic conductivity of spin-coated poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films by temperature-dependent conductivity measurements, has been analyzed. A detailed 3D morphological model was derived from topographic scanning tunneling microscopy (STM) and cross-sectional atomic force microscopy (AFM) images, which correlated the anisotropy, both in conductivity magnitude and in the conduction mechanism. Spin coated films of PEDOT:PSS formed a reasonably homogenous material in terms of electrical conductivity. It was observed that the vertical conductivity that is perpendicular to the substrate, can be up to three orders of magnitude lower than the lateral conductivity in the plane of the film. The macroscopic in-plane conductivity was found to be completely isotropic, and the ordering was found to be confined to randomly oriented micrometer-size domains.

Highly ordered thin films of organic materials are receiving a great deal of attention as active layers in a new generation of plastic electronic devices, particularly in organic field-effect transistors (OFETs). [1] Numerous organic-film preparation technologies have been tested over the past few decades. For commercial organic electronics, solution-processed, low-cost technologies such as spin-coating, inkjet printing, and screenprinting are preferred. [2] Mostly, these methods produce thin films with moderate structural order from soluble polymers and oligomers. The relevant physical parameters (e.g., chargecarrier mobilities) of thin organic films are strongly affected by the orientation, distribution, and size of the domains and domain boundaries, [3] and, more generally, by the degree of structural order. The endeavor to improve molecular alignment in active organic layers has led to the implementation of high-quality organic single crystals in OFETs with optimized performance. [4] However, recent methods for the fabrication of single-crystal devices are rather complex and inappropriate for practical applications. [5] Therefore, suitable organic compounds and preparation methods that yield highly ordered thin films are quite essential for progress in this field. In this paper, we present highly ordered thin films of 5,5″bis(5-hexyl-2-thienylethynyl)-2,2′:5′,2″-terthiophene (TR5-C6) prepared from solution by spin-coating and subsequent thermal treatment, and studied using X-ray diffraction (XRD) techniques. The calamitic TR5-C6 molecule consists of a central terthiophene unit with acetylene linkages connecting two terminal thiophene rings with hexyl end groups (Fig. 1a). The thermotropic liquid crystalline behavior of TR5-C6 has been studied by differential scanning calorimetry (DSC), and the mesophases have been assigned by polarized optical microscopy. During cooling, exothermic phase transitions from the nematic to the smectic C phase at 115°C, from the smectic C to the smectic B phase at 109°C, and from the smectic B