Triarylamine-based dual-function coadsorbents with extended π-conjugation aryl linkers for organic dye-sensitized solar cells

Triarylamine-based dual-function coadsorbents containing a carboxylic acid acceptor linked by extended pi-conjugation aryl linkers (e.g., phenylene: HC-A3, naphthalene: HC-A4 and anthracene: HC-A5) were newly designed and synthesized. They were used as coadsorbents in organic dye-sensitized solar cells (DSSCs) based on a porphyrin dye (hexyloxy-biphenyl-ZnP-CN-COOH (HOP)). For comparison, the pi-conjugated phenyl linker (HC-A3) previously developed by our group was also used as a coadsorbent. The structural effects on the photophysical and electrochemical properties and DSSC performance were systematically investigated. As a result, the DSSCs based on HC-A4 and HC-5 displayed power conversion efficiencies (PCEs) of 8.2% and 5.1%, respectively, while the HC-A3-based DSSC achieved a PCE of 7.7%. In the case of HC-A4, both the short-circuit photocurrent densities (J(sc)) and open-circuit voltages (V-oc) of DSSCs were simultaneously improved to a large extent due to the more effective prevention of pi-pi stacking of organic dye molecules and the better light-harvesting effect at short wavelengths. The HC-A5-based DSSC exhibited a much lower short-circuit current (J(sc)) and open-circuit voltages (V-oc) compared to the HC-A4-based DSSC, due to the fact that the dihedral angle of the pi-conjugated linkers was too high for electron injection into the TiO2 conduction band (CB) level. This had a reduced effect on preventing the pi-pi stacking of dye molecules, resulting in lower J(sc) and V-oc values. (C) 2014 Elsevier B.V. All rights reserved.