PHOTO-CARRIER DYNAMICS OF BLENDED AND MULTI-LAYERED FILMS OF ZINC PHTHALOCYANINE AND C-60 MEASURED BY TIME-RESOLVED TERAHERTZ SPECTROSCOPY

Date

2010-06-25

Author

Melinger, Joseph S.
Lane, Paul
Esentürk, Okan
Heilweil, Edwin

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We present a study of photo-induced carrier dynamics in organic thin films that contain zinc phthalocyanine (ZnPc) and buckminsterfullerene (C-60) investigated by ultrafast time resolved terahertz spectroscopy (TRTS). We compare two classes of films: 1) blend films of ZnPc and C-60 prepared by co-evaporation, and 2) superlattice films from alternating neat layers of ZnPc and C-60, where the individual layer varies in thickness between 2 nm and 40 nm. These films are model structures for the charge generation layers in organic photovoltaics, and their photo-carrier dynamics on a femtosecond to nanosecond timescale is of high interest. Using TRTS, which employs an optical pump pulse and a time delayed terahertz (THz) probe pulse, we find evidence for a short-lived charge transfer state of C-60 that decays within several picoseconds of excitation. Both blend and superlattice films have a long-lived (> 80 picoseconds) THz absorption that is dependent on the structure and composition of the films. The optimum composition for maximum photocarrier generation efficiency is a 1:1 blend of ZnPc and C-60. Amongst the layered films, we find that the photocarrier efficiency increases as the individual layer thickness decreases, with the film having ultrathin alternating 2 nm thick layers exhibiting the strongest THz absorption. A much stronger THz absorption signal was obtained for the 2 nm layered film than for the best blend film.

Subject Keywords

Charge exchange, Fullerenes, Optical pumping, Organic semiconductors, Semiconductor superlattices, Semiconductor thin films, Solar cells, Terahertz spectroscopy, Vacuum deposition, Zinc compounds

URI

https://hdl.handle.net/11511/41313

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Department of Chemistry, Conference / Seminar