Electronic devices
based on organic semiconductors are a fast-growing
field of technology. A detailed understanding of the interplay between
optical and electronic properties of organic molecular thin films
as well as the physical structure is highly beneficial for the optimization
of such devices. This requires investigations by means of different
yet complementary spectroscopic techniques, where the comparability
between the different data sets can become confusing. Consequently,
the core aspect of this work is the consistent unification of spectroscopic
data obtained by a diversity of experimental techniques within the
complementary pictures of molecular states and energy levels. The
confusion is obvious in the example of epitaxial films of tetraphenyldibenzoperiflanthene
(DBP) on graphite(0001) surfaces being discussed here. One puzzling
issue is the widening of the transport gap by around 0.6 eV during
film growth, whereas the optical gap remains virtually constant. Furthermore,
two-photon photoemission spectroscopy (2PPE) yields several features
related to the same unoccupied orbital, and it is a nontrivial task
to correlate them with the results of other spectroscopies. These
issues can be resolved when all spectroscopic data are consistently
interpreted in the framework of a theoretical model which was recently
introduced by us, taking the initial and final states of the underlying
probe processes into account. Applying that model, all peak shifts
are explained here consistently by means of polarization and charging
energies and further physical effects in context with the microscopic
structure of the DBP thin films.
A high conversion efficiency of 20.2% is achieved for simple structured-Si solar cells without a conventional anti-reflection layer. The ultralow-reflectance less than ∼3% is achieved by formation of a nanocrystalline Si (nc-Si) layer using the surface structure chemical transfer (SSCT) method which takes only 15 s. The nc-Si layer is passivated by phosphosilicate glass, while the rear Si surface is passivated by boron back-surface-field (B-BSF). By optimizing diffusion conditions, a high short-circuit current density of 41.8 mAcm −2 and improvement of an open-circuit voltage are achieved owing to enhancement of B-BSF and suppression of Auger recombination in the phosphorus-doped nc-Si layer.
Conventional acidic etching cannot form low reflectance surfaces from multi-crystalline silicon (multi-Si) wafers sawn by fixed abrasive (FXA) machining technology, which makes it difficult to replace the time- and cost-consuming free abrasive (FRA) machining method. In the present work, a nanocrystalline Si (nc-Si) layer is formed by use of the surface structure chemical transfer (SSCT) method, and the layer is used as a starting point of alkaline etching to fabricate low reflectance submicron texture on FXA multi-Si wafers. Although the nc-Si layer cannot be passivated by deposition of a silicon nitride (SiN) layer, the submicron textured surface formed from the nc-Si layer by alkaline etching can effectively be passivated by the SiN layer. Using the developed method, the SiN passivated submicron textured FXA multi-Si wafers possess both high minority carrier lifetime and lower reflectance than that of acidic textured FRA multi-Si wafers. The excellent passivation effect of the SiN layer on the low reflectance textured surface is attributed to the low interface state density of 1.2×1011 cm-2eV-1.
Self-assembled monolayers (SAMs) can be used for surface functional control to assist with pattern collapse prevention and as a protective layer to enable Area Selective Deposition (ASD). To be successful, these applications require the formation of a high-density, defect-free, so-called well-packed SAM at the nm scale. In this paper, we describe a method to map the nm scale defects of octadecyltrichlorosilane (ODTS) SAMs using a post-etching AFM analysis of the surface of the substrate and used this technique to develop a process to form high-density, defect-free SAM layer at the nm scale. This was achieved by optimizing the water concentration in the solvent for the precursor solution and annealing after SAM formation.
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