Aggregation-Free ZnO Nanocrystals Coupled HMP-2 Dye of Higher Extinction Coefficient for Enhancing Energy Conversion Efficiency

A novel and highly efficient dye, Ru(H₂dcbpy)(4-(4-(N,N-di(p-hexyloxyphenyl)amino)styryl)-4′-methyl-2,2′-bipyridine)(NCS)₂, HMP-2, with extinction coefficients of about 33 260 L·mol⁻¹·cm⁻¹ at 534 nm and about 20 000 L·mol⁻¹·cm⁻¹ at 490 nm, is designed and further applied onto ZnO nanocrystals for dye-sensitized solar cells application. ZnO nanocrystals of a few nanometers are spin coated onto an indium−tin oxide substrate for forming about 2.5 μm uniform film thickness. Change in the surface appearance of ZnO in the presence of N3 and in newly designed HMP-2 dye is illustrated. Structural elucidation of the newly developed HMP-2 dye is presented in depth. A ZnO nanoparticle electrode is dipped in HMP-2 dye and in commercially used N3 dyes for 24 h to see the influence of dye structure on the surface aggregation effect due to insulating Zn⁺/dye complex layer formation. Interestingly, the ZnO nanocrystal electrode surface with HMP-2 dye is almost free of this efficiency-diminishing effect, and a solar-to-electrical conversion efficiency of 4.03%, which is about 40-fold times higher than that of N3 dye, is obtained.