A Benzodithiophene-Based Novel Electron Transport Layer for a Highly Efficient Polymer Solar Cell

We designed and synthesized a novel conjugated polyelectrolyte (CPE), poly{3-[2-[4,8-bis(2-ethyl-hexyloxy)-6-methyl-1,5-dithia-s-indacen-2-yl]-9-(3-dimethylamino-propyl)-7-methyl-9H-fluoren-9-yl]-propyl}-dimethyl-amine (PBN). We employed PBN as an electron-transporting layer on a ZnO layer and constructed a highly efficient, inverted structure device consisting of a mixture of poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) and PC70BM, achieving a high power conversion of up to 8.6%, constituting a 21.1% improvement over the control device performance (7.1%) prepared without a PBN layer. This result was ascribed to the reduced interfacial resistance and the improved charge transport and collection through the PBN electron transport layer.