title: Upconversion-Triggered Charge Separation in Polymer Semiconductors.
abstract: Upconversion is a unique optical property that is driven by a sequential photon pumping and generation of higher energy photons in a consecutive manner. The efficiency improvement in photovoltaic devices can be achieved when upconverters are integrated since upconverters contribute to the generation of extra photons. Despite numerous experimental studies confirming the relationship, fundamental explanations for a real contribution of upconversion to photovoltaic efficiency are still in demand. In this respect, we suggest a new approach to visualize the upconversion event in terms of surface photovoltage (SPV) by virtue of Kelvin probe force microscopy (KPFM). One of the most conventional polymer semiconductors, poly(3-hexyl thiophene) (P3HT), is employed as a sensitizer to generate charge carriers by upconverted light. KPFM measurements reveal that the light upconversion enabled the formation of charge carriers in P3HT, resulting in large SPV of -54.9 mV. It confirms that the energy transfer from upconverters to P3HT can positively impact the device performance in organic solar cells (OSCs).
authors.forename: Yu Jin
authors.identifier: http://orcid.org/0000-0001-8116-3618
authors.initials: YJ
authors.lastname: Jang
authors.forename: Eunah
authors.initials: E
authors.lastname: Kim
authors.affiliation: School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, Republic of Korea.
authors.forename: Seonghyeon
authors.initials: S
authors.lastname: Ahn
authors.forename: Kyungwha
authors.initials: K
authors.lastname: Chung
authors.forename: Jihyeon
authors.initials: J
authors.lastname: Kim
authors.forename: Heejun
authors.initials: H
authors.lastname: Kim
authors.forename: Huan
authors.initials: H
authors.lastname: Wang
authors.affiliation: School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, Republic of Korea.
authors.forename: Jiseok
authors.initials: J
authors.lastname: Lee
authors.forename: Dong-Wook
authors.initials: DW
authors.lastname: Kim
authors.forename: Dong Ha
authors.identifier: http://orcid.org/0000-0003-0444-0479
authors.initials: DH
authors.lastname: Kim