Effect of substituents of phenyl of π-linkage in carbazole sensitizers on the photovoltaic performance of the dye-sensitized solar cells

Four novel carbazole dyes with various substituents, i.e., dyes CA, CO, CP and CB with substituents of alkyl, oxyalkyl, pillar[5]arene and hydrogen, respectively, are designed and synthesized to investigate the relationship between the substituents on phenyl of pi-linkage and performances of dye-sensitized solar cells. With the different degree of deviation from planarity of the pi-linkage by the substituents, the HOMO level and bandgap of the dyes were selectively tuned. The dye CO shows lower HOMO (0.66 V) and E0-0 (2.23 eV) than that of CB (HOMO: 0.97 V, E0-0: 2.52 eV), leading to the enhanced light harvesting ability and thus the highest power conversion efficiency among the four dyes. Further study shows that the bridge of carbon atoms between the substituents and phenyl in the dyes CA and CP decreased the short-circuit photocurrent, lower their performance. This study shows that the substituents can affect the torsion angle of pi-linkage, the charge recombination, the electron lifetime for photoexcited electron injection into the TiO2 and VOC, which paves the way to design dyes for highly efficient solar cells.

Automated summary

This study investigates the impact of various substituents on the phenyl of pi-linkage of carbazole dyes on the performance of dye-sensitized solar cells. The research shows that the substituents can selectively tune the HOMO level and bandgap of the dyes, affecting their light harvesting ability and conversion efficiency. Additionally, the study reveals that the bridge of carbon atoms between the substituents and phenyl can decrease the short-circuit photocurrent and lower the overall performance of the dyes.