highly ordered and directional intermolecular π-π interactions and hydrogen-bonding network allow the formation of quantum confined structures within the peptide self-assemblies, thus decreasing the band gaps of the superstructures into semiconductor regions. As a result of the diverse architectures and ease of modification of peptide self-assemblies, their semiconductivity can be readily tuned, doped, and functionalized. Therefore, this family of electroactive supramolecular materials may bridge the gap between the inorganic semiconductor world and biological systems. Characterization To design and characterize organic semiconductors used for optoelectronic applications one should first measure the absorption and photoluminescence spectra using commercial instrumentation. However, in order to find out if a material acts as an electron donor or acceptor one has to determine the energy levels for hole and electron transport. The easiest way of doing this, is to employ cyclic voltammetry. However, one has to take into account that using this technique the experimentally determined oxidation and reduction potential are lower bounds because in voltammetry the radical cations and anions are in a polar fluid solution and are, thus, solvated. Such a solvation effect is absent in a solid specimen. The relevant technique to energetically locate the hole transporting states in a solid sample is UV-photoemission spectroscopy. The equivalent technique for electron states is inverse photoemission. There are several techniques to measure the mobility of charge carriers. The traditional technique is the so-called time of flight (TOF) method. Since this technique requires relatively thick samples it is not applicable to thin films. Alternatively, one can extract the charge carrier mobility from the current flowing in a field effect transistor as a function of both the source-drain and the gate voltage. One should be aware, though, that the FET-mobility is significantly larger than the TOF mobility because of the charge carrier concentration in the transport channel of a FET (see below). Other ways to determine the charge carrier mobility involves measuring space charge limited current (SCLC) flow and "carrier extraction by linearly increasing voltage (CELIV). In order to characterize the morphology of semiconductor films, one can apply atomic force microscopy (AFM) scanning electron microscopy (SEM) and Grazing-incidence small-angle scattering (GISAS). Charge transport In contrast to organic crystals investigated in the 1960-70s, organic semiconductors that are nowadays used as active media in optoelectronic devices are usually more or less disordered. Combined with the fact that the structural building blocks are held together by comparatively weak van der