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SYOP: Symposium Organic Photovoltaics: From Single Molecules to Devices

SYOP 1: Organic Photovoltaics I

SYOP 1.11: Vortrag

Mittwoch, 25. März 2009, 16:30–16:45, ZEU 222

Highly doped layers as efficient electron-hole conversion contact for tandem organic solar cells — •Ronny Timmreck, Selina Olthof, Moritz Riede, and Karl Leo — Institut für angewandte Photophysik, TU Dresden, Dresden, Germany

To achieve high power conversion efficiencies with stacked organic solar cells, several requirements concerning their layer structure have to be fulfilled. A key feature is an efficient conversion contact at the interface between the single solar cells of a stacked cell: Here, an electron current has to be converted into a hole current without loss of energy. We investigate such contacts for small-molecule organic solar cells and present an approach adopted from inorganic tandem solar cells by using highly doped organic layers. We also compare metal-cluster based conversion contacts reported in literature to our new approach. For this purpose, comparable structures are characterised by UPS, by I-V-characteristics of organic p/n-heterojunctions, and by I-V-characteristics of corresponding solar cells. The experiments show that our approach is superior to the metal cluster based approach, e.g. it allows a full addition of the open circuit voltage Voc of the subcells independent from the used organic materials. It is thus possible to avoid the metal clusters which allows for a wider choice of materials and has advantages for future mass production. Using these results, a possible working mechanism of these contacts is discussed: high recombination rates at the conversion contact result in low sheet resistances and a removal of quasi-Fermi level splitting such that no reverse voltage occurs which would reduce Voc of the stacked solar cell.