POM-based dyes featuring rigidified bithiophene π linkers: potential high-efficiency dyes for dye-sensitized solar cells†
A series of POM-based dyes with a triphenylamine electron donor group, cyanoacrylic acid electron acceptor group and different π linkers of thiophene derivatives were systematically investigated to analyze the influence of a rigidified bithiophene with fastening atoms (C and N) on the performance of dye-sensitized solar cells (DSSCs) based on density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The interfacial electron transfer (IET) processes were evaluated, which have not been significantly investigated previously. We can see that the electrons in dyes 2, 4 and 5 are almost completely injected after 100 fs, thus leading to fast IET. Dye 2 not only has a lower interaction energy for the most stable dimer configuration compared to dye 1, but also has a larger short-circuit photocurrent density, JSC, and open-circuit photovoltage, VOC, resulting from the insertion of a polyoxometalate (POM) group. Compared with dye 3 containing a 2,2′-bithiophene π linker, its two counterparts (dyes 4 and 5) with rigidified bithiophene π linkers tend to accelerate the IET process, as well as slow the electron recombination, and thus improve the performance of the DSSCs. In particular, dye 4 with a rigidified bithiophene π linker fastening using a C atom obtains a larger JSC and VOC compared to that of dye 5 with a N atom rigidified bithiophene π linker.