New molecular donors with dithienopyrrole as the electron-donating group for efficient small-molecule organic solar cells

Abstract

Six new molecules with donor-acceptor-acceptor (D-A-A) configuration bearing coplanar electron-donating dithieno[3,2-b:2′,3′-d]pyrrole (DTP) or aryl-substituted DTP as the D unit and the electron-withdrawing pyrimidine-dicyanovinylene or benzothiadiazole-dicyanovinylene as the A-A block are synthesized. The introduction of aryl groups (p-tolyl or p-anisolyl) onto the α position of DTP is found to greatly benefit the chemical stability and extend the molecular conjugation of the DTP-based D-A-A molecules. The observed broad absorption spectra and anisotropic molecular orientation in the thin films allow for these new D-A-A molecules to perform good capability of light harvesting. These new D-A-A donors are subject to the fabrication of vacuum-processed small-molecule organic solar cells (SMOSCs). The results showed that the structural modulation on the central A block (pyrimidine versus benzothiadiazole) as well as the terminal substitution (p-tolyl versus p-anisolyl) give an evident trade-off between the open circuit voltage (V oc) and short circuit current density (Jsc) values. Among them, SMOSC-adopted D-A-A molecule TDPM composed of a p-tolyl terminal group and a D-A-A configuration of DTP-pyrimidine-dicyanovinylene as the electron donor combined with C70 as the electron acceptor shows a Jsc of 11.34 mA/cm2, a Voc of 0.94 V, and a fill factor (FF) of 0.52, giving a best power conversion efficiency (PCE) as high as 5.6%. © 2014 American Chemical Society.