title: Band-Tail Transport of CuSCN: Origin of Hole Extraction Enhancement in Organic Photovoltaics.
abstract: Copper thiocyanate (CuSCN) is known as a promising hole transport layer in organic photovoltaics (OPVs) due to its good hole conduction and exciton blocking abilities with high transparency. Despite its successful device applications, the origin of its hole extraction enhancement in OPVs has not yet been understood. Here, we investigated the electronic structure of CuSCN and the energy level alignment at the poly(3-hexylthiophene-2,5-diyl) (P3HT)/CuSCN/ITO interfaces using ultraviolet photoelectron spectroscopy. The band-tail states of CuSCN close to the Fermi level (EF) were observed at 0.25 eV below the EF, leading to good hole transport. The CuSCN interlayer significantly reduces the hole transport barrier between ITO and P3HT due to its high work function and band-tail states. The barrier reduction leads to enhanced current density-voltage characteristics of hole-dominated devices. These results provide the origin of hole-extraction enhancement by CuSCN and insights for further application.
authors.affiliation: Institute of Physics and Applied Physics, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea.
authors.forename: Minju
authors.initials: M
authors.lastname: Kim
authors.affiliation: Institute of Physics and Applied Physics, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea.
authors.forename: Soohyung
authors.initials: S
authors.lastname: Park
authors.affiliation: Institute of Physics and Applied Physics, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea.
authors.forename: Junkyeong
authors.initials: J
authors.lastname: Jeong
authors.affiliation: Institute of Physics and Applied Physics, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea.
authors.forename: Dongguen
authors.initials: D
authors.lastname: Shin
authors.affiliation: Department of Physics, Pohang University of Science and Technology , Pohang 37673, Korea.|Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science , Pohang 37673, Korea.
authors.forename: Jimin
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Physics, Pohang University of Science and Technology , Pohang 37673, Korea.|Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science , Pohang 37673, Korea.
authors.forename: Sae Hee
authors.initials: SH
authors.lastname: Ryu
authors.affiliation: Department of Physics, Pohang University of Science and Technology , Pohang 37673, Korea.|Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science , Pohang 37673, Korea.
authors.forename: Keun Su
authors.initials: KS
authors.lastname: Kim
authors.affiliation: Department of Physics, Kangwon National University , 1 Gangwondaehak-gil, Chuncheon-si, Gangwon-do 24341, Korea.
authors.forename: Hyunbok
authors.initials: H
authors.lastname: Lee
authors.affiliation: Institute of Physics and Applied Physics, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea.
authors.forename: Yeonjin
authors.initials: Y
authors.lastname: Yi