Peripheral group effects on the photophysical and photovoltaic properties of bulk-heterojunction type solar cells based on star-shaped conjugate molecules with triphenylamine core

In this study we prepared three star-shaped, triphenylamine-cored conjugated molecules, possessing thienylenevinylene units as conjugated π bridges and thienyl, 2-ethylhexyl cyanoacetate, and 1,3-diethyl-2-thiobarbituric acid moieties, respectively, as peripheral groups - for use as donor materials in small molecule/fullerene bulk heterojunction-type organic photovoltaic cells (OPVs). The peripheral groups affected the UV-Vis absorption behavior and electrochemical properties of star-shaped molecules, and photovoltaic performance of the star-shaped molecules based OPVs. The wavelength of maximum absorption for star-shaped molecule with 1,3-diethyl-2-thiobarbituric acid moiety was red-shifted relative to those of molecules with thienyl and 2-ethylhexyl cyanoacetate groups, while molecule with thienyl moiety exhibited the largest hole mobility. The photovoltaic properties of cells incorporating molecule with thienyl group and a fullerene derivative were better than those containing corresponding molecule with 2-ethylhexyl cyanoacetate/fullerene or molecule with 1,3-diethyl-2-thiobarbituric acid/fullerene blends. An OPV featuring molecule with thienyl group/fullerene derivative (1:3, w/w) as the active layer exhibited a power conversion efficiency of 1.43%, a short-circuit current density of 5.23 mA/cm2, an open-circuit voltage of 0.73 V, and a fill factor of 0.37. © 2015 Elsevier B.V. All rights reserved.