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t g a r t , D 70550 S t u t t g a r t , Germany AbstractOrganic photovoltaic thin film s t r u c t u r e s made by vacuum vapor deposition have been studied. From t h e spectral response as a function of t h e absorption coefficient we conclude t h a t electron -hole generation takes place a t t h e interface between t h e organic thin film and one or b o t h of t h e semitransparent cover electrodes. The observed s h o r t circuit currents, however, are t o o large to be explained on t h e basis of a direct light-induced charge transfer at t h e organic thin film/ electrode interface. Rather, a contribution of t h e bulk-absorbed photons is necessary t o account f o r the observed quantum yield. Transfer of t h e energy t o t h e interface sites can be explained by diffusional migration of excitons. The efficiency of charge separation can be improved by combining donor a n d acceptor type partners in organic double layers. The efficiency of power conversion, however, n o t only depends on a suitable choice of t h e absorption spectra and of t h e ionic energy levels of t h e materials employed, b u t also on t h e internal cell resistance, a f a c t t h a t calls f o r high charge carrier mobilities, and hence f o r using materials with crystal structures t h a t allow s t r o n g n-electron interactions, and f o r deposition in high chemical purity and s t r u c t u r a l perfection.

Krypton clusters are ionized and excited with synchrotron radiation in the energy range 22.0–28.5 eV. In threshold photoelectron photoion coincidence spectra (TPEPICO) resonancelike structures are observed and can be attributed to excitations of valence excitons (additional to ionization) as well as core excitons. Metastable decay is also detected and is found to be initiated by excitation of the valence levels only.