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Proceedings Paper

Low-level optical absorption phenomena in organic thin films for solar cell applications investigated by highly sensitive photocurrent and photothermal techniques
Author(s): Ludwig J. Goris; Ken Haenen; Milos Nesladek; A. Poruba; M. Vanecek; P. Wagner; Laurence J. Lutsen; Jean Manca; Dirk Vanderzande; Luc De Schepper
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Paper Abstract

Optical absorption phenomena and in particular sub band gap absorption features are of great importance in the understanding of processes of charge generation and transport in organic pure and composite semiconductor films. To come towards this objective, an alternative and high sensitive spectroscopic approach is introduced to examine the absorption of light in pure and compound organic semiconductors. Because sub band gap absorption features are typically characterized by very low absorption coefficients, it is not possible to resolve them using common transmission and reflection measurements and high sensitive alternatives are needed. Therefore, a combination of photocurrent (Constant Photocurrent Method CPM/Fourier Transform Photocurrent Spectroscopy FT-PS) and photothermal techniques (Photothermal Deflection Spectroscopy PDS) has been used, increasing sensitivity by a factor of thousand, reaching detectable absorption coefficients ((E) down to 0.1 cm-1. In this way, the dynamic range of measurable absorption coefficients is increased by several orders of magnitude compared to transmission/reflection measurements. These techniques have been used here to characterize ground state absorption of thin films of MDMO-PPV, PCBM and a mixture of both materials in a 1:4 ratio, as typically used in a standard active layer in a fully organic solar cell. The spectra reveal defect related absorption phenomena and significant indication of existing interaction in the ground state between both materials, contrary to the widely spread conviction that this is not the case. Experimental details of the techniques and measurement procedures are explained.

Paper Details

Date Published: 8 September 2004
PDF: 10 pages
Proc. SPIE 5464, Organic Optoelectronics and Photonics, (8 September 2004); doi: 10.1117/12.547276
Show Author Affiliations
Ludwig J. Goris, Limburgs Univ. Centrum (Belgium)
Ken Haenen, Limburgs Univ. Centrum (Belgium)
Milos Nesladek, Limburgs Univ. Centrum (Belgium)
IMEC (Belgium)
A. Poruba, Institute of Physics (Czech Republic)
M. Vanecek, Institute of Physics (Czech Republic)
P. Wagner, Limburgs Univ. Centrum (Belgium)
Laurence J. Lutsen, IMEC (Belgium)
Jean Manca, Limburgs Univ. Centrum (Belgium)
IMEC (Belgium)
Dirk Vanderzande, Limburgs Univ. Centrum (Belgium)
IMEC (Belgium)
Luc De Schepper, Limburgs Univ. Centrum (Belgium)
IMEC (Belgium)

Published in SPIE Proceedings Vol. 5464:
Organic Optoelectronics and Photonics
Paul L. Heremans; Michele Muccini; Hans Hofstraat, Editor(s)

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