In this paper we discuss the optimization of various parameters which govern the behaviour of polymer based and organic photovoltaic cells. General mechanisms leading to the generation of charge carriers and the related loss factors are detailed. Theoretical electrical parameters for bilayer and interpenetrating networks of donors and acceptors (open circuit voltages) are established along with current versus voltage characteristics. An equivalent circuit to a solar cell, considering the effects of shunt resistance across the whole layer, is elaborated. After modelling optical interference and its effects on the photocurrent spectrum, orders of magnitude of the required parameters are established for an efficient solar cell. Deviations from optimal values and their effects on the current-voltage characteristics are discussed. Ageing and degradation effects, and calculations demonstrating the necessary photophysical requirements to achieve long-term stable devices are presented.

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Organic photovoltaic solar cells bere an important potential of development in the search for low-cost modules for the production of domestic electricity. We review the principles and techniques needed for their development: organic semiconductors, their transport properties and photophysical characteristics, photovoltaic molecule and polymer structures, device technologies, electrical and optical behaviour of the cells, state of the art, limitations and perspectives. Despite some recent record efficiencies, research on organic solar cells is still in its infancy when stability and efficiency have to be compared with the performances of silicon cells. A nominal 10% solar efficiency is the research target for the next few years.

Although compounds 1 and 2 (see Figure) have comparable conjugation lengths, the characterization of vacuum evaporated thin solid films shows that the star‐shaped geometry of compound 1 favors a preferential horizontal orientation of the molecules onto the surface of the substrate, which results in a increase of the efficiency of the corresponding heterojunction solar cells under white‐light illumination by a factor of 20.