Organic Dye for Highly Efficient Solid‐State Dye‐Sensitized Solar Cells

Dye sensitized solar cells are an interesting low cost alter native to conventional solar cells. Efficiencies over 10 % have been achieved. [1,2] Advantageous is the replacement of the liquid electrolyte in these devices with a solid charge carrier material to avoid any sealing and long term stability prob lems. In 1998 Bach et al. [3] demonstrated that the electrolyte can be replaced by a hole conductor. Here we report a very efficient solid state solar cell with the amorphous organic hole transport material 2,2¢,7,7¢ tetrakis (N,N di p methoxyphenyl amine)9,9¢ spirobifluorene (spiro OMeTAD) as hole conduc tor and for the first time an organic metal free indoline dye as sensitizer. Record efficiencies for this type of cell of over 4 % over the solar spectrum were reached. Until now, sensitization using organic dyes has not been as efficient as using ruthenium dyes, which have been success fully applied previously. Metal free dyes such as perylene de rivatives, [4] coumarin dyes, [5] porphyrin dyes, [6] and cyanine and merocyanine dyes [7] have been used as sensitizers, but did not achieve the same solar conversion efficiency as ruthenium dyes. The efficiencies achieved in this work with the indoline dye (D102) are even higher than the highest currently report ed values for ruthenium dye sensitized solid state cells. In ad dition, this dye has the advantage that it can be produced at low cost, because it does not contain the expensive rare metal ruthenium and it is easy to synthesize. Up to now the best results reported with spiro OMeTAD as a hole conductor are efficiencies of 3.2 %. [8] In that work the dye uptake and open circuit voltage were optimized by a sil ver complexation. In the case of the indoline dye we were able to reach an efficiency of just over 4 % without further optimi zation. This shows the extremely high potential of the indoline dye as a sensitizer in solid state dye sensitized solar cells. In doline dyes have previously been used in dye sensitized solar cells with a liquid electrolyte. [9,10] There also they showed a good performance of up to g = 6.1 % conversion efficiency compared to 6.3 % for a N3 dye sensitized cell. [9] Solid state devices usually have a lower performance, which is not the case here with an extraordinary efficiency of 4 %, which ap proaches that of their liquid …