The influence of alkyl side chains on molecular packing and solar cell performance of dithienopyrrole-based oligothiophenes

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 4; no. 27; pp. 10514 - 10523
• Main Authors: Schulz, Gisela L, Kar, Prasenjit, Weidelener, Martin, Vogt, Astrid, Urdanpilleta, Marta, Linden, Mika, Mena-Osteritz, Elena, Mishra, Amaresh, Baeuerle, Peter
• Format: Journal Article
• Language: English
• Published: 01.01.2016
• Subjects: Current density; Devices; DTP; Electric potential; Oligomers; Photovoltaic cells; Solar cells; Thiophenes
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c6ta03453e

The synthesis of a series of dithieno[3,2-b:2',3'-d]pyrrole (DTP) containing A-D-A oligomers for use in solution-processed bulk heterojunction solar cells is presented. This series allows investigation of the effect of alkyl chains attached to the thiophene moieties or the nitrogen of the DTP unit on the thermal and physical properties of the oligomers. The photoactive layers were probed using absorption spectroscopy, grazing incident X-ray diffraction, and atomic force microscopy. From these experiments, it was found that the hexyl chains attached to the thiophene units are instrumental in obtaining good packing and high fill factors in the solar cell devices. For the fabrication of solar cells, both PEDOT:PSS and V sub(2)O sub(5) were investigated as hole transport layers and PDMS was employed as a solvent additive. High open-circuit voltages of up to 1.1 V, moderate short-circuit current densities, and high fill factors of up to 0.63 were obtained yielding power conversion efficiencies as high as 5.3%.