title: Efficient low bandgap polymer solar cell with ordered heterojunction defined by nanoimprint lithography.
abstract: In this work, we demonstrate the feasibility of using nanoimprint lithography (NIL) to make efficient low bandgap polymer solar cells with well-ordered heterojunction. High quality low bandgap conjugated polymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) nanogratings are fabricated using this technique for the first time. The geometry effect of PCPDTBT nanostructures on the solar cell performance is investigated by making PCPDTBT/C70 solar cells with different feature sizes of PCPDTBT nanogratings. It is found that the power conversion efficiency (PCE) increases with increasing nanograting height, PCPDTBT/C70 junction area, and decreasing nanograting width. We also find that NIL makes PCPDTBT chains interact more strongly and form an improved structural ordering. Solar cells made on the highest aspect ratio PCPDTBT nanostructures are among the best reported devices using the same material with a PCE of 5.5%.
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Physics, §Department of Electrical Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Kamil
authors.initials: K
authors.lastname: Mielczarek
authors.forename: Anvar
authors.initials: A
authors.lastname: Zakhidov
authors.forename: Walter
authors.initials: W
authors.lastname: Hu
keywords: chain ordering; morphology of polymer solar cell; nanoimprint lithography; nanostructure geometry effect; ordered heterojunction