The energy required to power an autonomous field device can be drawn from its environment by means of energy harvesting. Outdoors, one abundant and ubiquitous source of energy is solar irradiation, which can be reliably converted into electricity by solar cells. In principle, this is also true indoors if artificial light sources produce sufficient optical irradiation. Different solar cell materials can play off their individual strengths in these different use cases. Since ambient optical irradiation usually is an intermittent phenomenon, a solar powered field device has to include an energy storage solution for bridging gaps that occur in energy harvesting. In this study, different solar cell materials and energy storage solutions are discussed and evaluated quantitatively according to data sheet information. According to calculations for an assumed continuous power consumption of an autonomous field device of 1 mW for a period of 10 years, a solar panel of 4 × 4 cm² in the outdoor case and 20 × 20 cm² in the indoor case can deliver the required energy. Along with an energy storage system consisting of a 100 F supercapacitor and a primary backup cell, solar energy harvesting for autonomous field devices seems technically feasible.

A new perylene diimide derivative, namely N,N 0diallyl-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxylic acid diimide (phenoxy-allyl-PTCDI, abbreviated PA-PTCDI), is introduced. The investigations presented in this paper aim at finding a molecule for use as a sensitzer in thin film silicon solar cells in order to enhance efficiency. The synthesis is described along with optical and electrochemical measurements of PA-PTCDI in solution. A good agreement is found between the measured data and theoretical calculations. The molecule is characterized further by optical and photoemission data on thin films, which also show that the dye can be sublimed in vacuum. The interface between the dye and silicon is investigated on the model system Si(111):H with synchrotron-induced photoemission spectroscopy. The result is an electronic lineup with the gap centers of silicon and PA-PTCDI almost at identical positions and thus very similar band discontinuities from the lowest unoccupied molecular orbital (LUMO) to the conduction band as well as from the highest occupied molecular orbital (HOMO) to the valence band. This clearly permits a transfer of photogenerated electrons and holes from PA-PTCDI to silicon. The experimental valence band discontinuity matches very well the value calculated for a very similar PTCDI molecule.

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