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Proceedings Paper

Continuous-wave photoinduced absorption studies in long lived photoexcitation of π-conjugated polymer and fullerene blended films
Author(s): X. Yang; H. Li; Y. C. Wang; R. Z. Wang; C.-X. Sheng
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Paper Abstract

The long lived phtoexcitation (polarons) dynamics that range from microseconds to milliseconds in a typical organic photovoltaic (OPV) material, the blends of regio-regular poly (3-hexylthiophene) (RR-P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), have been investigated using continuous-wave photoinduced absorption (cw-PIA) spectroscopy. In this time regime, whether above-gap (AG) or below-gap (BG) excitation, the delocalized polarons (DP) and localized polarons (LP) all exhibit dispersive bimolecular recombination process which is limited by multi-trap states; however, compared to AG, BG excitation presented the narrower distribution profile in trap polaron states. Furthermore, the recombination in RR-P3HT/PCBM films was weak temperature dependence with small thermal activation energy, the value Δ for DPs and LPs of 25 meV (45 meV) and 13 meV (42 meV) using AG (BG) excitation, respectively. We considered that polarons from BG excitation are not intrinsically different with polarons from AG one in millisecond time regime, therefore may contribute to the power conversion efficiency using appropriate materials and device structures. For completeness, cw-PIA spectroscopy of poly[2-methoxy, 5-(2’-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) and PCBM blended films with amorphous morphology were also studied. It is found that polarons also exhibited multi-trap limited bimolecular recombination, but Δ for polarons in amorphous MEH-PPV/PCBM was up to ~160 meV. We concluded that polarons in RR-P3HT/PCBM blend are basically transport by tunneling, but the recombination in MEH-PPV/PCBM blend near room temperature is mainly thermal activated process. Overall, it is demonstrated that cw-PIA spectroscopy with thermal-activated-recombination analysis can be applied to evaluate polymer (dis)order in bulk heterojunction films.

Paper Details

Date Published: 2 September 2014
PDF: 9 pages
Proc. SPIE 9284, 7th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronics Materials and Devices for Sensing and Imaging, 92840V (2 September 2014); doi: 10.1117/12.2067585
Show Author Affiliations
X. Yang, Nanjing Univ. of Science and Technology (China)
H. Li, Nanjing Univ. of Science and Technology (China)
Y. C. Wang, Nanjing Univ. of Science and Technology (China)
R. Z. Wang, Nanjing Univ. of Science and Technology (China)
C.-X. Sheng, Nanjing Univ. of Science and Technology (China)


Published in SPIE Proceedings Vol. 9284:
7th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronics Materials and Devices for Sensing and Imaging
Yadong Jiang; Junsheng Yu; Bernard Kippelen, Editor(s)

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