title: Charge Generation Dynamics in Efficient All-Polymer Solar Cells: Influence of Polymer Packing and Morphology.
abstract: All-polymer solar cells exhibit rapid progress in power conversion efficiency (PCE) from 2 to 7.7% over the past few years. While this improvement is primarily attributed to efficient charge transport and balanced mobility between the carriers, not much is known about the charge generation dynamics in these systems. Here we measured exciton relaxation and charge separation dynamics using ultrafast spectroscopy in polymer/polymer blends with different molecular packing and morphology. These measurements indicate that preferential face-on configuration with intermixed nanomorphology increases the charge generation efficiency. In fact, there is a direct quantitative correlation between the free charge population in the ultrafast time scales and the external quantum efficiency, suggesting not only the transport but also charge generation is key for the design of high performance all polymer solar cells.
authors.forename: Bhoj R
authors.initials: BR
authors.lastname: Gautam
authors.affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 305-701, Republic of Korea.
authors.forename: Changyeon
authors.initials: C
authors.lastname: Lee
authors.forename: Robert
authors.initials: R
authors.lastname: Younts
authors.affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 305-701, Republic of Korea.
authors.forename: Wonho
authors.initials: W
authors.lastname: Lee
authors.forename: Evgeny
authors.initials: E
authors.lastname: Danilov
authors.affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 305-701, Republic of Korea.
authors.forename: Bumjoon J
authors.initials: BJ
authors.lastname: Kim
authors.forename: Kenan
authors.initials: K
authors.lastname: Gundogdu
keywords: all polymer solar cells; charge generation/recombination; nanomorphology; polymer packing; ultrafast spectroscopy