Novel Near-Infrared Squaraine Sensitizers for Dye-Sensitized Solar Cells
Chuanjiang Qin a, Liyuan Han a
a Photovoltaic Materials Unit, National Institute for Materials Science, Sengen 1-2-1, Tsukuba, 305, Japan
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Poster, Chuanjiang Qin, 198
Publication date: 1st March 2014

Dye-sensitized solar cells (DSCs) have received increasing attention owing to their potential use in low-cost production of renewable energy and in large-area, flexible, colourful, lightweight devices.[1] Nowadays, the main challenges of researches on organic sensitizers in the field of dye-sensitized solar cells are developing efficient and stable near-infrared (NIR) absorption sensitizers for panchromatic harvesting solar spectrum by itself or co-sensitized with another sensitizer, and ensuring appropriate energy levels for efficient electron injection and regeneration.

Among different kinds of NIR dyes, squaraine dyes are most promising candidates as the red and NIR sensitizers for DSCs, due to its simple synthetic routes as well as excellent absorption property and stability.[2] In order to further increase efficiency, there are many groups have adopted different strategies to extend π-conjugated structure of squaraine sensitizers for bathochromic shifting of the absorption spectrum for harvesting much broad sunlight. However, the incident photon-to-current conversion efficiency (IPCE) is still low due to unmatched energy levels (most cases are lower than 50% at 700 nm).

Recently, we developed new molecular design strategy by modifying the central moiety of squaraine, therefore, to tune the strength of electron-withdrawing and π-conjugation length, to modify the HOMO and LUMO energy levels.[3] The absorption maximum is red-shifted to more than 686 nm via a simple molecular design strategy. A solar cell sensitized with new squaraine dye shows a broader IPCE spectrum (from 400 to 800 nm) and a higher IPCE in the long-wavelength region (71% at 700 nm). Following this molecular design strategy, a new molecular design on near-infrared squaraine dyes is further developed to fine tune energy levels and absorption spectrum. The power conversion efficiency and device stability of DSC based on HSQ4 are improved with a high IPCE response (80%) at a wavelength of 720 nm due to the ideal energy levels and molecular structure. In this report, I will show our recent progresses and details of these novel NIR squaraine dyes, as well as their application on the transparent DSCs. [4,5]

[1] O’Regan B.; Grätzel M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 1991, 353, 737-740. [2] Qin C.; Wong W.; Han L. Squaraine dyes for Dye-Sensitized Solar Cells: Recent Advances and Further Challenges. Chem. A Asian J. 2013, 8, 1706-1719. [3] Qin C.; Numata Y.; Zhang S.; Islam A.; Yang X.; Sodeyama K.; Tatayama 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. [4] Qin C.; Numata Y.; Zhang S.; Yang X.; Islam A.; Zhang K.; Chen H.; Han L. Novel Near-Infrared Squaraine Sensitizers for Stable and Efficient Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2013, DOI: 10.1002/adfm.201303769. [5] Zhang K.; Qin C.; Yang X.; Zhang S.; Islam A.; Chen H.; Han L. High-Performance, Transparent Dye-Sensitized Solar Cells for See-through Photovoltaic Windows. Adv. Energy Mater. 2014, submitted
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