Highly efficient mesoscopic dye-sensitized solar cells based on donor-acceptor-substituted porphyrins.

Dye-sensitized solar cells (DSCs) are currently attracting considerable attention because of their high light-to-electricity conversion efficiencies, ease of fabrication, and low production costs. Many recent efforts have been devoted to the development of new and efficient sensitizers that are suitable for practical use. Among the investigated compounds, ruthenium sensitizers have been distinguished by attaining more than 11% efficiencies. Organic sensitizers have also attracted great interest because of their modest cost, ease of synthesis and modification, large molar absorption coefficients, and satisfactory stability. Organic dyes with conversion efficiencies in the range of 5–10% have been reported. Porphyrins show strong absorption and emission in the visible region as well as tunable redox potentials. These properties lead to promising applications in many areas, such as optoelectronics, chemosensors, and catalysis. Self-assembled porphyrin molecular structures play a key role in solar energy research as the photosynthetic systems of bacteria and plants contain chromophores based on lightharvesting porphyrins, which collect solar energy and convert it efficiently into chemical energy. Various artificial photosynthetic model systems have been designed and synthesized in order to elucidate the factors that control the photoinduced electron-transfer reaction. Inspired by the efficient energy transfer in naturally occurring photosynthetic reaction centers, numerous porphyrins and phthalocyanines have been synthesized and tested in dye-sensitized solar cells. The best-performing porphyrin dyes have been reported to have conversion efficiencies in DSCs in the range of 5–7%. A recently reported series of porphyrin dyes with donor–acceptor (D–A) substituents exhibit promising photovoltaic properties. Herein we report the achievement of an 11% solar-toelectric power conversion efficiency under standard (AM 1.5G, 100 mWcm 2 intensity) reporting conditions by using a judiciously tailored porphyrin dye, YD-2. To the best of our knowledge, this is the first time such a high efficiency has been obtained with a ruthenium-free sensitizer. The structure of the YD-2 porphyrin used in this study is shown in Scheme 1. A diarylamino donor group attached to the porphyrin ring acts as an electron donor, and the