Role of the organic-cathode interface on the performance of organic solar cells

M. DOLORES PEREZ; KRYSTAL SLY; ELIZABETH I. MAYO; MARK E. THOMPSON

Boston, MA

Congreso; MRS 2006 Fall Meeting; 2006

Materials Research Society

Organic photovoltaics have the potential for development of inexpensive and efficient solar cells. Processes occurring after the absorption of a photon within the solar cell are still not completely understood. In particular, the process by which the free electron is collected at the metal organic interface is still under debate. It is usually considered that charge collection at this interface is a very efficient process and its effect on cell performance is generally disregarded. This work illustrates that charge collection is highly dependant on the nature of the metal-organic interface. It has been shown that different metals (e.g. Al vs Ag) result in significantly different cell efficiencies, with cells using Ag as the cathode performing better than those using Al. In an effort to understand this effect, different compositions of these two metals have been tested as cathodes. In order to elucidate differences between the role of the EBL/cathode interface from the role of the cathode/electrode contact, Al and Ag were deposited sequentially with variation in the layer thicknesses, as well as the order of deposition. The cathode materials were also codeposited to form a mixed Al/Ag cathode. The thickness of the overall metallic layer was maintained at 1000 Å throughout all experiments. Results will be presented that show the clear dependence of solar cell performance on the cathode architecture and composition. These striking observations suggest that not only do the bulk properties of the metals strongly influence the nature of cell performance, but also that the molecular properties of the metal-organic interface can not be ignored.