Effect of electron rich π-linkers on the functional properties of dyes featuring dithieno[3,2-b:2′,3′-d]pyrrole donor

In this paper, organic dyes containing dithienopyrrole (DTP) donor, linkers such as thiophene or dithienopyrrole and cyanoacrylic acid acceptor are reported. The impact of different π-linkers on photophysical, electrochemical and photovoltaic properties is studied. The dyes containing dithienopyrrole linker showed improved light harvesting efficiency and reduced oxidation potentials than the thiophene analogs. The major absorption originates from the charge transfer transition, which shifts progressively to red region on increasing the number of heteroaromatic linkers. Additionally, the presence of N-fluorenyldithieonopyrrole in the conjugation bridge is beneficial to retard the charge recombination process. Therefore, the dye containing a dithienopyrrole linker showed the highest efficiency of 5.94% in the series attributable to its high J_SC and V_OC values. However, a dye containing two dithienopyrrole units in the conjugation pathway exhibited low power conversion efficiency irrespective of its intense absorption attributable to the low charge collection efficiency and reduced electron lifetime.