title: Behavior of Photocarriers in the Light-Induced Metastable State in the p-n Heterojunction of a Cu(In,Ga)Se2 Solar Cell with CBD-ZnS Buffer Layer.
abstract: We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with a chemical bath deposition (CBD)-ZnS buffer layer grown with varying ammonia concentrations in aqueous solution. The solar cell performance was degraded with increasing ammonia concentration, due to actively dissolved Zn atoms during CBD-ZnS precipitation. These formed interfacial defect states, such as hydroxide species in the CBD-ZnS film, and interstitial and antisite Zn defects at the p-n heterojunction. After light/UV soaking, the CIGS solar cell performance drastically improved, with a rise in fill factor. With the Zn-based buffer layer, the light soaking treatment containing blue photons induced a metastable state and enhanced the CIGS solar cell performance. To interpret this effect, we suggest a band structure model of the p-n heterojunction to explain the flow of photocarriers under white light at the initial state, and then after light/UV soaking. The determining factor is a p+ defect layer, containing an amount of deep acceptor traps, located near the CIGS surface. The p+ defect layer easily captures photoexcited electrons, and then when it becomes quasi-neutral, attracts photoexcited holes. This alters the barrier height and controls the photocurrent at the p-n junction, and fill factor values, determining the solar cell performance.
authors: ICT Materials & Components Research Laboratory, Electronics and Telecommunications Research Institute , Daejeon 34129, Korea.
authors: Woo-Jung
authors: WJ
authors: Lee
authors: ICT Materials & Components Research Laboratory, Electronics and Telecommunications Research Institute , Daejeon 34129, Korea.|Department of Physics, Kongju National University , Gongju 32588, Korea.
authors: Hye-Jung
authors: HJ
authors: Yu
authors: ICT Materials & Components Research Laboratory, Electronics and Telecommunications Research Institute , Daejeon 34129, Korea.
authors: Jae-Hyung
authors: JH
authors: Wi
authors: ICT Materials & Components Research Laboratory, Electronics and Telecommunications Research Institute , Daejeon 34129, Korea.
authors: Dae-Hyung
authors: DH
authors: Cho
authors: ICT Materials & Components Research Laboratory, Electronics and Telecommunications Research Institute , Daejeon 34129, Korea.
authors: Won Seok
authors: WS
authors: Han
authors: Institute of Physics and Applied Physics, Yonsei University , Seoul 03722, Korea.
authors: Jisu
authors: J
authors: Yoo
authors: Institute of Physics and Applied Physics, Yonsei University , Seoul 03722, Korea.
authors: Yeonjin
authors: Y
authors: Yi
authors: Department of Physics, Kongju National University , Gongju 32588, Korea.
authors: Jung-Hoon
authors: JH
authors: Song
authors: ICT Materials & Components Research Laboratory, Electronics and Telecommunications Research Institute , Daejeon 34129, Korea.|Department of Advanced Device Engineering, Korea University of Science and Technology , Daejeon 34113, Korea.
authors: Yong-Duck
authors: YD
authors: Chung
keywords: Cu(In,Ga)Se2; chemical bath deposition; defect layer; light/UV soaking effect; p-n heterojunction; photocarriers