Organic semiconductors are materials of great promise for the use in solar cells, TV displays and home lighting. The main advantage over their inorganic counterparts is that they are abundant and devices based upon them can be easily and cheaply processed from solution by well established techniques such as spin-coating and ink-jet printing. Since the operation of all electronic devices is based on the process of charge transport in the material, it is important to understand these processes in order to be able to rationally design organic electronic devices. The main research objective of this proposal is to develop a theoretical and computational framework that links the atomic structure of the organic material to its electrical properties. Such a development would enable the researchers to predict the charge transport properties of the material based on the chemical formula of the polymer or molecule.We plan to investigate: (i) the nature of charge carriers in organic crystals and their electrical transport properties; (ii) the electronic structure and carrier transport in completely disordered polymers; (iii) carrier transport in crystalline regions of a polymer material; (iv) the role of grain boundaries in organic crystals and the role of interfaces between ordered and disordered regions in polymer materials. We will use the combination of the methods for large scale electronic structure and electronic transport calculations recently developed by the applicant, as well as some standard methods such as density functional theory, molecular dynamics, configuration Monte Carlo, etc.The realization of the project is expected to lead to the reintegration of the applicant into the ERA and to the formation of his own research group. This will contribute to EU scientific excellence and EU competitiveness by the virtue of the applicant's expertise in important, but largely unexplored field of simulations of electronic transport in organic materials.