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Advances in Optical Technologies
Volume 2012 (2012), Article ID 316045, 10 pages
Research Article

Carrier Formation Dynamics of Organic Photovoltaics as Investigated by Time-Resolved Spectroscopy

1Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba 305-8571, Japan
2Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), University of Tsukuba, Tsukuba 305-8571, Japan
3Photovoltaic Materials Unit, National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan

Received 9 April 2012; Accepted 17 May 2012

Academic Editor: Saulius Juodkazis

Copyright © 2012 Kouhei Yonezawa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Bulk heterojunction (BHJ) based on a donor (D) polymer and an acceptor (A) fullerene derivative is a promising organic photovoltaics (OPV). In order to improve the incident photon-to-current efficiency (IPCE) of the BHJ solar cell, a comprehensive understanding of the ultrafast dynamics of excited species, such as singlet exciton (D*), interfacial charge-transfer (CT) state, and carrier (D+), is indispensable. Here, we performed femtosecond time-resolved spectroscopy of two prototypical BHJ blend films: poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend film and poly(9,9′-dioctylfluorene-co-bithiophene) (F8T2)/[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) blend film. We decomposed differential absorption spectra into fast, slow, and constant components via two-exponential fitting at respective probe photon energies. The decomposition procedure clearly distinguished photoinduced absorptions (PIAs) due to D*, CT, and D+. Based on these assignments, we will compare the charge dynamics between the F8T2/PC70BM and P3HT/PCBM blend films.