Effect of Substituents of Thienylene-Vinylene-Thienylene-Based Conjugated Polymer Donors on the Performance of Fullerene and Nonfullerene Solar Cells

Abstract

Semiconducting polymers consisting of (E)-1,2-di(thiophen-2-yl)ethene (TVT) derivatives and benzo[1,2-b:4,5-b']-dithiophene with conjugated thiophene side chains (BDTT) were designed and synthesized to investigate the effect of fluorine and cyano groups in the 3-position of the thiophene ring in TVT on the photovoltaic properties. The corresponding PBDTT-TVT, PBDTT-FTVT, and PBDTT-CNTVT copolymers containing TVT, difluoro TVT (FTVT), and dicyano TVT (CNTVT), respectively, demonstrated considerable variations in optical, electrochemical, morphological, and charge transporting properties. PBDTT-FTVT showed suitable frontier orbital energy levels, favorable face-on orientation, and a well-mixed and smooth morphology in the blends with 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC) and [6,6]-phenyl-C-71-butyric acid methyl ester (PCBM). In contrast, PBDTT-CNTVT showed unfavorable frontier orbital energy levels and bimodal orientation in the thin-film state, which interrupted efficient charge transport in organic photovoltaic devices. The device fabricated using PBDTT-FTVT exhibited the highest power conversion efficiency (PCE) of up to 6.50% with ITIC and a slightly lower PCE of 6.35% with PCBM.