A step closer to solar cells-Dye sensitized solar cells

Science 4 November 2011: 
Vol. 334 no. 6056 pp. 629-634 
DOI: 10.1126/science.1209688

• RESEARCH ARTICLE

Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency

1. Aswani Yella¹, 
2. Hsuan-Wei Lee², 
3. Hoi Nok Tsao¹, 
4. Chenyi Yi¹, 
5. Aravind Kumar Chandiran¹,
6. Md.Khaja Nazeeruddin¹, 
7. Eric Wei-Guang Diau³,*, 
8. Chen-Yu Yeh²,*, 
9. Shaik M Zakeeruddin¹,*, 
10. Michael Grätzel¹,*

ABSTRACT

The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co^(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.