Lifetime and stability of organic solar cells
ved Golnaz Sherafatipour

Organic photovoltaic (OPV) is an emerging economically competitive photovoltaic technology that has advantages over conventional inorganic PV technology including low fabrication cost, lightweight, semi-transparency and mechanical flexibility. Despite these advantages, OPVs have comparably low power conversion efficiencies and rather short lifetimes, which are the most critical factors hampering their application. In order to overcome these barriers and close the gap between laboratory achievements and industrial scale requirements, a detailed understanding of the device degradation mechanism is required. Charge transfer (CT) states, representing intermediate states between exciton dissociation and recombination at donor-acceptor interface, play hereby a crucial role.

The main purpose of this PhD project, as part of the FP7 ITN network THINFACE, is to study the degradation mechanism and charge transfer loss, taking place at the donor-acceptor heterointerface. We established some new methods for obtaining information about charge-transfer states in organic solar cells, which is a fundamental need for gaining a deeper insight into the physical working principle of the cells, here including also device efficiency and stability, which is strongly related to the aim of this PhD work. These investigations are done by means of sensitive external quantum efficiency and electroluminescence measurements, as well as surface-sensitive microscopy techniques.
Vejleder: Morten Madsen

mechanical stability of Organic Solar cells
Ved Michela Prete

Organic solar cells (OPVs) are considered, nowadays, a promising alternative to the inorganic PVs thanks to their low fabrication cost, the easy processability and tunability to different applications. In respect to the latest, organic materials allowed, in fact, the fabrication of flexible and stretchable devices opening the door to the possibility of mass production. These advantages are still limited by the ongoing improvement on the stability and efficiency of the organic devices. Although the efficiency has reached 12%, the final commercialization of the OPVs is still dependent on their stability. If different have been, in the past years, the photochemical stability studies, still few are the reported analysis on the mechanical properties of the organic devices. It is very important to understand the mechanical properties of the materials utilized, as much as understanding the results of the mechanical stress on flexible cells that is affecting the performances of the device over time.

The main goal of the research project is to gain insight into the mechanical properties of flexible organic solar cells and to explore the possibilities of increasing the mechanical durability and stability of the cells while maintaining scalability and high electrical device performance. The project therefore encompasses work and specific objectives on determining the influences from both photochemical and mechanical stressing of flexible organic solar cells, and on applying specific additives that stabilize the cells against these degradation factors, both individually and combined. The work builds upon initial work on photochemical stabilization of organic solar cells, from where the initially tested photochemically stabilizing additives are chosen.

Vejledere: Morten Madsen og Vida Engmann

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