title: Study of band structure at the Zn(S,O,OH)/Cu(In,Ga)Se2 interface via rapid thermal annealing and their effect on the photovoltaic properties.
abstract: This study focused on understanding the mechanisms of the photovoltaic property changes in Zn(S,O,OH)/Cu(In,Ga)Se2 solar cells, which were fabricated via annealing, using reflection electron energy loss spectroscopy (REELS), ultraviolet photoelectron spectroscopy (UPS), low temperature photoluminescence (LTPL), and secondary ion mass spectroscopy (SIMS). A pinhole-free Zn(S,O,OH) buffer layer was grown on a CIGS absorber layer using the chemical bath deposition (CBD). When the Zn(S,O,OH) film was annealed until 200 °C, the Zn-OH bonds in the film decreased. The band gap value of the annealed film decreased and the valence band offset (VBO) value at the Zn(S,O,OH)/CIGS interface with the annealed film increased. Both results contribute to the conduction band offset (CBO) value at the Zn(S,O,OH)/CIGS interface and, in turn, yield a reduction in the energy barrier at the interface. As a result of the annealing, the short circuit current (JSC) and quantum efficiency (QE) values (400-600 nm) of the cell increased due to the improvement in the electron injection efficiency. However, when the Zn(S,O,OH) film was annealed at 300 °C, the cell efficiency declined sharply due to the QE loss in the long wavelength region (800-1100 nm). The SIMS analysis demonstrated that the Cu content in the CIGS bulk decreased and the Cu element also diffused into CIGS/Mo interface. Through LTPL analysis, it was seen that the considerable drop of the Cu content in the CIGS bulk induced a 1.15 eV PL peak, which was associated with the transition from a deep donor defect to degrade the quality of the CIGS bulk. Accordingly, the series resistance (RS) and efficiency of the cell increased.
authors.affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology , 291 Daehak ro, Yuseong gu, Daejeon, Republic of Korea 305-701.
authors.forename: Dong Hyeop
authors.initials: DH
authors.lastname: Shin
authors.forename: Seung Tae
authors.initials: ST
authors.lastname: Kim
authors.forename: Ji Hye
authors.initials: JH
authors.lastname: Kim
authors.forename: Hee Jae
authors.initials: HJ
authors.lastname: Kang
authors.forename: Byung Tae
authors.initials: BT
authors.lastname: Ahn
authors.forename: Hyuksang
authors.initials: H
authors.lastname: Kwon
mesh_terms: D003300:Copper / Q000737:chemistry*; D005708:Gallium / Q000737:chemistry; D007204:Indium / Q000737:chemistry; D049329:Nanostructures / Q000737:chemistry; D012643:Selenium / Q000737:chemistry; D012993:Solar Energy; D013696:Temperature; D017971:Tin Compounds / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
chemical_list: D017971:Tin Compounds; D007204:Indium; C109984:indium tin oxide; D003300:Copper; D005708:Gallium; D012643:Selenium; D015032:Zinc