An imidazolium iodide salt as a bifunctional co-adsorbent for quasi-solid-state dye-sensitized solar cells: improvements of electron lifetime and charge collection efficiency

Abstract

To promote dye regeneration, 1,2-dimethyl-3-acetyl-imidazolium iodide (DMA-II) is synthesized and applied as a bifunctional co-adsorbent for quasi-solid-state dye-sensitized solar cells. The DMA-II can be co-adsorbed onto the TiO₂ surface with the dye molecules due to the presence of a carboxy group, and the coadsorption can thus reduce the dye aggregation. Moreover, the I⁻ species existing in the co-adsorbent are close to the dye molecules, which is favorable for fast dye regeneration and hence photocurrent generation. As compared to the typically used co-adsorbent, deoxycholic acid (DCA) that does not contain iodide, the DMA-II co-adsorbent enhances the electron lifetime and electron collection yield significantly, because the iodide in the co-adsorbent can quickly reduce the dye cation formed upon electron injection to its original neutral state. As a result, the DMA-II co-adsorbent (1 mM) achieves a power conversion efficiency of 8.97% for quasi-solid-state dye-sensitized solar cells under AM 1.5 G (100 mW cm⁻²) illumination, which is higher than that (7.35%) without co-adsorption and outperforms DCA co-adsorption at 1 mM (7.81%) and at 20 mM (8.24%). Importantly, the quasi-solid-state dye-sensitized solar cell with DMA-II coadsorption demonstrates good long-term stability with an efficiency drop less than 10% after one-sun soaking for 1000 h.