Molecular Design of D-pi-A Type II Organic Sensitizers for Dye Sensitized Solar Cells

Four new type II organic dyes with D-pi-A structure (donor-p-conjugated-acceptor) and two typical type II sensitizers based on catechol as reference dyes are synthesized and applied in dye sensitized solar cells (DSCs). The four dyes can be adsorbed on TiO2 through hydroxyl group directly. Electron injection can occur not only through the anchoring group (hydroxyl group) but also through the electron-withdrawing group (?CN) located close to the semiconductor surface. Experimental results show that the type II sensitizers with a D-pi-A system obviously outperform the typical type II sensitizers providing much higher conversion efficiency due to the strong electronic push-pull effect. Among these dyes, LS223 gives the best solar energy conversion efficiency of 3.6%, with Jsc=7.3 mA center dot cm-2, Voc=0.69 V, FF=0.71, the maximum IPCE value reaches 74.9%.