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Project A6:

High performance organic solar cells with tailored light trapping structures

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The development of flexible and low-cost opto-electronic devices based on organic materials, like organic light emitting diodes (OLEDs), organic field effect transistors (OFETs), or especially photo¬voltaic cells, is of key importance. With the advent of ecologic energy devices, efficient low-cost photo¬voltaic devices are urgently needed. Besides the synthesis of highly effective charge generating and transporting materials, the structure of these devices is also crucial, especially when light harvesting is considered. Despite ongoing optimisation efforts in material and component design, organic photovoltaic devices are still less efficient than their inorganic counterparts. Nevertheless, they are considered the next-generation solar cells in view of their light weight, their mechanical flexiblility, and their unmatched low costs.

In this joint project, experimental and theoretical expertise of three groups will be combined to develop high-performance organic thin film bulk heterojunction solar cells with dramatically improved charge generation and transport. In a first step, we will incorporate bay-fused oligo (perylene bisimide) deri¬vatives as strong, self-assembled light harvesting materials into bulk heterojunction cells. Further, related donor-accep¬tor (D-A) copolymers will be synthesised and integrated. In addition, light trapping structures will elon¬gate the optical path inside the cell and thus vastly improve the light harvesting properties of the cell exploiting principles of nonlinear optics. Different structuring techniques will be employed and compared and the best grating pa-rameters investigated. Computer simulations based on first principles will guide the optimisation of photo-struc¬tured gratings and of the material composition for best charge generation and transport. The final goal is a highly efficient hole transporting hybrid system, that can be structured by photophysical means, paving the way for a breakthrough in organic solar cells in terms of efficiency, stability, and cost effectiveness.