Density Functional Theory Investigation of Co-sensizatioin Effect in Ru/Organic Dye-Sensitized Solar Cell

Yusuke Ootani^a^,^b, Liyuan Han^a^,^b, Yoshitaka Tateyama^a^,^b^,^c^,^d, Keitaro Sodeyama^a^,^c

^aNational Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305, Japan

^bCREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, 333-0012, Japan

^cKyoto University, Japan, Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245, Japan

^dPRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, 333-0012, Japan

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Yusuke Ootani, 381
Publication date: 5th February 2015

A co-sensitization technique, in which mixed dyes are used to sensitize a semiconductor, is widely used to improve an incident photon-to-current conversion efficiency (IPCE) of dye-sensitized solar cells (DSCs). However, all co-sensitized DSCs do not necessarily show improved IPCE, and the detailed design principle is still an open question. Recently two Ru/organic co-sensitized DSCs were developed with a Ru dye of N3, and two organic dyes, HSQ1 and SQ1.¹ In 500–600 nm spectral region, where HSQ1 cannot contribute to the IPCE, N3-HSQ1 co-sensitized DSC showed improved IPCE over N3 sensitized DSC. On the other hand N3-SQ1 co-sensitized DSC did not show the improvement. This rsult indicates that not only the absorption property but also other factors are important for the co-sensitization. In this work we compare the two organic dyes, HSQ1 and SQ1, by means of density functional theory calculations. Single dye adsorption sturctures of HSQ1 and SQ1, the co-adsorption structures of N3-HSQ1 and N3-SQ1 were analyzed. In the co-adsorption structure of N3-HSQ1, a steric hindrance keeps N3–HSQ1 distance longer. On the other hand, SQ1 forms a hydrogen bond (HB) with N3 (Figure). It is well known that the binding interaction such as HB leads to formation of dye aggregation, which lowers the IPCE. The HB affects absorption spectrm of SQ1. While an absorption peak position of HSQ1 does not change upon the co-adsorption, the absorption peak of SQ1 shifts to short wavelength. This shift is undesirable because SQ1 is designed to extend an absorption range to long wavelength region. These results suggest that the slight molecular configuration difference affects the co-adsorption structures, leading to the differences in the IPCE of co-sensitized DSC.²
Co-adsorption structures of N3-HSQ1 (a) and N3-SQ1 (b).
[1] Qin, C; Numata, Y.; Zhang, S.; Islam, A.; Yang, X.; Sodeyama, K.; Tateyama, Y.; Han, L. A Near-Infrared cis-Configured Squaraine Co-Sensitizer for High-Efficiency Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2013, 23, 3782-3789. [2] Ootani. Y.; Sodeyama, K.; Han, L.; Tateyama, Y. in preparation.

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