Future Prospects of Organic and Hybrid Solar Cells for Next Generation Photovoltaics
Hiroshi Segawa a
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
Invited Speaker, Hiroshi Segawa, presentation 168
Publication date: 1st March 2014

Next-generation solar cells based on new concepts and/or novel materials are currently attracting wide interests. In this study, several types of next generation organic photovoltaics are investigated.

Among the emerging solar cells, dye-sensitized solar cells (DSSCs) have received much attention as the low-cost solar cells. However, the energy conversion efficiency should be improved for the practical use. In order to improve the energy conversion efficiency, the extension of absorption range of the sensitizers to near-infrared regions is an important issue. In our study, panchromatic photoelectric conversion up to around 1000 nm has been accomplished by the use of new sensitizers DX1, 2, and 3. The panchromatic DSSC with DXs are useful for a series-connected tandem solar cell. We prepared the various tandem solar cells showing a high overall power conversion efficiency (η) of about 15%.

We have developed organic photovoltaics based on the surface complexes formed of TiO2 with dicyanomethylene compounds (TCNXs). The surface complexes exhibit broad absorption bands in the visible to near-infrared region due to interfacial charge-transfer transitions from the surface bound TCNX to the conduction band of TiO2. In the solar cell using the surface complex, charge separation occurs directly by the charge transfer transitions. It was found that the spectral sensitivity of the solar cell can be controlled by adjusting the π- conjugation length of TCNX. Ionization potential  measurements revealed that the effects arise from the increase of the HOMO energy of the surface  bound TCNX with extension of the π- conjugation system and the resultant red-shift of the charge transfer absorption band.

Since the mechanisms of DSSC include electrochemical reaction, it can be hybridized with an  electrochemical storage battery. We have reported a three-electrode solar rechargeable battery,  namely "energy-storable dye-sensitized solar cell (ESDSSC)", composed of the photoanode, the counter electrode and the charge-storage electrode. The ESDSSC not only generates output power, but also stores the electricity by itself. Therefore the output voltage and power of the ES-DSSC can be stabilized under various photoirradiation conditions. Additionally, design panels of the ES-DSSC is constructed as shown in the Figure 1.

Acknowledgements: I would like to thank Prof. T. Kubo, Prof. S. Uchida, Prof. J. Fujisawa, Dr. J.
Nakazaki, Dr. T. Kinoshita, Dr. Y. Saito, Dr. M. Sasaki, and Ms. R. Ogura for their collaborations. This work was supported by the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program) from the Japanese Government.


Colorful Design Panels of Energy-Storable Dye-sensitized Solar Cells with a Built-in Storage Battery.
1) Takumi KINOSHITA, Joanne Ting DY, Satoshi UCHIDA, Takaya KUBO, Hiroshi SEGAWA, Nature Photonics 2013, 7(7), 535-539. 2) Sergei MANZHOS, Ryota JONO, Koichi YAMASHITA, Jun-ichi FUJISAWA, Morio NAGATA, Hiroshi SEGAWA, Journal of Physical Chemistry C 2011, 115(43), 21487-21493.
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