Search

One of the major improvements for CdTe solar cells is the increase of the current density by enhancing the transparency of the buffer layer. CdS, with its 2.4 eV band gap, results in being opaque at low wavelength regions. For this reason, in order to gain in blue and UV light, extremely thin CdS has to be applied, if the buffer is not substituted with other materials. On the other hand, by thinning the CdS layer we create pinholes also due to the wide intermixing of CdTe and CdS layers and subsequently consumption of CdS. For this reason we have applied and compared different CdS post-deposition treatments in order to stabilize the layer and avoid excess intermixing. Treatments at temperatures above 500 °C in an argon and chlorine atmosphere on 80 nm thick CdS have led to the fabrication of more stable samples compared to untreated CdS, resulting in improved performance with a 10% increase in current density and a 5% increase in open circuit voltage and fill factor. Moreover, light transmission of the CdS treated layers from 300 to 450 nm is increased by about 10%. In this paper, a study of treated thin CdS with recrystallization treatments is presented; the layers have been analysed by means of X-ray photoelectron spectroscopy, X-ray diffraction and atomic force microscopy. Finished CdTe devices made on thin CdS are characterized in terms of current-voltage and quantum efficiency.

We demonstrate field effect transistors based on organic semiconductor molecules dispersed in a self-organized polystyrene (PS) latex bead matrix. An aqueous colloidal composite made of PS and tetrahexylsexithiophene (H4T6) is deposited with a micropipet into the channel of a bottom-contact field effect transistor. The beads self-organize into a network whose characteristic distances are governed by their packing. The semiconductor molecules crystallize in the interstitial voids, leading to the growth of large interconnected domains. Depending on the bead size and the ratio between H4T6 and PS, the fraction of the different phases in the polymorph can be controlled. In the transistors where the H4T6 metastable "red phase" is the largest, the device response and the charge mobility are comparable to those of sexithienyl thin films grown by high-vacuum sublimation.

Single molecule magnets (SMM) are a class of molecules exhibiting magnetic properties similar to those observed in conventional bulk magnets, but of molecular origin. SMMs have been proposed as potential candidates for several technological applications that require highly controlled thin films and patterns. Here we present an overview of the most important approaches for thin film growth and micro(nano)-patterning of SMM, giving special attention to Mn(12) based molecules. We present both conventional approaches to thin film growth (Langmuir-Blodgett, chemical approach, dip and dry, laser evaporation), patterning (micro-contact printing, deposition on patterned surface, moulding of homogeneous films) and new methods specifically developed for SMM (lithographically controlled wetting, lithographically controlled de-mixing).

We present a method that uses patterned self-assembled monolayers (SAMs) of alkanethiolates on silver as templates to fabricate ordered two-dimensional arrays of solid CdS nanoclusters. The CdS is grown by electrochemical atomic layer epitaxy inside sub-micrometric stripes of hexadecanthiol SAM fabricated by microcontact printing. CdS ultrathin films grow and self-organize into an ordered pattern of nanoclusters. This pattern exhibits both lithographically imposed ordered structures and a self-affine structure along the direction perpendicular to the stripes. On the contrary, along the direction parallel to the stripes no spatial correlation among the clusters has ever been observed.

A new class of chiral oligothiophenes is described. Mono-, bi-, ter-, and quarterthiophenes have been linked to enantiopure trans- 1,2-cyclohexanediamine (DACH) via diamino or diimino moieties. The stereochemistry of DACH, the type of linker, and oligothiophene size determine the conformational flexibility of these molecules and consequently their molecular and supramolecular helicity in solution and in the solid state. The case of diaminobis(bithiophene), which inverts helicity and shows chiral amplification in the transition from solution to film, is described in detail. Based on the combined use of circular dichroism in solution and in the solid state, single-crystal/thin-film X-ray diffraction, and polarized optical microscopy, a working mechanism has been proposed to explain this unexpected behavior.