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

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.

Electrifying Organic Synthesis

“…They are used for the synthesis of pharmaceuticals,30 natural products,31 dyes,32 polymers,33 and functional materials 34. Therefore, an easy access to aniline derivatives is highly desired.…”

New generation solar cells: concepts, trends and perspectives

“…As a result, a V OC of nearly 1 V was attained, leading to a PCE of 11.9%. 89 Further improvements in the structural optimization of Por dyes involved the introduction of benzothiadiazole (BTD) as an electron acceptor, which yielded porphyrins GY50 90 and SM315 75 (Fig. 12).…”

Brief Overview of Dye-Sensitized Solar Cells

“…The organic sensitizer D35, equipped with bulky alkoxy groups, efficiently suppresses recombination, allowing the use of cobalt redox mediators with relatively small steric bulk. Based on these concepts Grätzel and co-workers published, in November 2011, the new DSC efficiency world record of 12.3% (Yella et al 2011). The record cell is based on a Co-complex redox electrolyte in combination with two cosensitizing dyes (a porphyrin and an organic dye) facilitated with alkoxy steric groups.…”

“…With our breakthrough of using one-electron transfer redox systems such as Co-complexes, in combination with a dye, which efficiently prevents the recombination loss, we may now have found the path to increase the efficiency significantly (Feldt et al 2010). With the recent world record of 12.3 by Grätzel and co-workers (Yella et al 2011) using Co-complexes, the main direction of the research field is now to explore this path.…”