title: Thorough subcells diagnosis in a multi-junction solar cell via absolute electroluminescence-efficiency measurements.
abstract: World-wide studies on multi-junction (tandem) solar cells have led to record-breaking improvements in conversion efficiencies year after year. To obtain detailed and proper feedback for solar-cell design and fabrication, it is necessary to establish standard methods for diagnosing subcells in fabricated tandem devices. Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements. We demonstrate that the absolute-EL-quantum-efficiency measurements provide I-V relations of individual subcells without the need for referencing measured I-V data, which is in stark contrast to previous works. Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the "balance sheets" of tandem solar cells.
authors.affiliation: 1] Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan [2] Department of Electronic Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China.
authors.forename: Shaoqiang
authors.initials: S
authors.lastname: Chen
authors.affiliation: Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhu
authors.affiliation: Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yoshita
authors.affiliation: 1] Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan [2] Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-2-9 Machiikedai, Koriyama, Fukushima 963-0215, Japan.
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Mochizuki
authors.affiliation: Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Changsu
authors.initials: C
authors.lastname: Kim
authors.affiliation: Institute for Solid State Physics, University of Tokyo, and JST-CREST, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Akiyama
authors.affiliation: Japan Aerospace Exploration Agency (JAXA), Tsukuba, Ibaraki 305-8505, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Imaizumi
authors.affiliation: Institute for Chemical Research, Kyoto University, and JST-CREST, Uji, Kyoto 611-0011, Japan.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Kanemitsu