Ion-coordinating sensitizer in solid-state hybrid solar cells.

The solid state dye sensitized solar cell is one of the most promising organic based device concepts which demonstrates solar power conversion efficiencies in excess of 4%. The basic strategy of this hybrid system is that light is absorbed in a dye to form an excited electronic state, termed an exciton. Electron transfer takes place from the excited dye molecule to an inorganic semiconductor, where it is transported to and collected at an electrode. Subsequent hole transfer from the oxidized dye to a hole transporting organic molecule or polymer takes place, where the hole is transported to and collected at the counter electrode. The fundamental advant age of this system over two component systems 7] is that the electron and hole transporting components are spatially separated by the dye molecules, which hugely suppresses charge recombination and allows efficient charge collection through microns thick material. Furthermore, the efficiency of such devices has been found to dramatically improve with the addition of various additives to the hole transporting material, with themost efficient devices incorporating specific quantities of ionic salts and electrochemical dopants. This “cocktail” of additives has been fine tuned and optimized for the current system. However, the precise function of each component is, as yet, not fully understood. Herein, we report a new charge transfer sensitizer with an ion complex ing moiety formed by oxyethylene side groups. Lithium coordination to the backbone of this dye induces a striking improvement in the photovoltage and performance, with voltages of nearly 900 mV regularly achieved and efficiencies improved from 3.2 to 3.8% (under 100 mWcm 2 simulated air mass (AM) 1.5 solar conditions) for the lithium coordinating sensitizer as compared with a noncoordinating analogue. A staggering record efficiency of 4.6% is achieved under 10 mWcm 2 simulated AM 1.5 illumination. Our supramolec ular approach to the self assembly of functional compo nents 11] opens new avenues to control charge separation and recombination at the interface, and gives us a more comprehensive understanding of the mechanisms occurring within this class of solar cells. The chemical structures of the dyes used for sensitization are shown in Scheme 1. Z907 is an amphiphilic ruthenium