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Energy Materials Laboratory © 2014, EML | All Rights Reserved.

Inorganic Chalcogenide Energy Devices

Our research goal is developing novel materials for energy applications with the current emphasis on non-toxic, earth-abundant, and low-cost
compounds for photovoltaic and photocatalytic applications.

Inorganic Chalcogenide Energy Devices

Cu(In,Ga)Se2 (CIGS) is a leading thin film PV technology which exhibits power conversion efficiencies over 22%. Also since CIGS is a potential of BIPV applications, we are researching low temp CIGS and Cd free buffers. Additionally, to realize mass deployment of a PV technology economically, PV devices must exhibit high efficiencies and consist of materials that are earth-abundant and non-toxic. The kesterite Cu2ZnSn(S,Se)4 (CZTSSe) compound has emerged as a potential candidate to reach this goal. We are working on improving the performance of SnS (SnSe) and Sb2S3 (Sb2Se3) as well. Additionally, we are exploring thermoelectric properties of SnSe.

  • CIGS

    The two main topics that our lab currently interested in are post deposition treatment (PDT) and developing new buffer materials

    Alkali post-deposition technique is needed highly-efficient CIGS solar cells prepared on a flexible substrate. Alkali elements, such as Na, K, Rb, Cs, has been known to passivate surface/interface. We are currently working on improving efficiencies with new alkali elements using a vacuum thermal co-evaporation technique and trying to understand the mechanism behind the beneficial effects of alkali treatments.

    Second topic is development of new buffer layer. The most common buffer layer that forms a p-n junction with CIGS absorber is CdS because of high effiencies reported with the CdS buffer. However, for safety concerns, there is need for developing Cd-free buffer materials. We are working on ZnO-based buffer materials such as ZnSnO, ZnTiO as a potential candidate to replace CdS.

  • CZTS Solar Cells

    Cu2ZnSn(S,Se)4 (CZTSSe) has attracted massive attention as an alternative for CdTe and CIGS because it consists of earth-abundant and non-toxic elements. It also holds a promise for high efficiency due to its proper optoelectronic properties such as a high absorption coefficient (~104-105 cm-1) and a tunable band gap (1.0-1.5 eV depending on S/Se ratio). However, compared to other thin film solar cell technologies such as CdTe, CIGS, and perovskite solar cells, CZTSSe suffers from the high open-circuit voltage (Voc) deficit (Eg/q - Voc, where q is the elemental charge), which hinders further improvement in device performance. Our group is currently working on resolving Voc deficit issue in CZTSSe solar cells with various approaches concerned with passivating the absorber (increasing carrier concentration, grain boundary passivation, and band gap engineering) as well as the interfaces.

    Related publications

    - J. Kim, B. Shin. Electron. Mater. Lett. (2017). https://doi.org/10.1007/s13391-017-7118-1
    - J. Kim, S. Park, S. Ryu, J. Oh, B. Shin. Prog. Photovolt: Res. Appl. 25, 308 (2017).
    - J. H. Kim, S.-Y. Choi, M. Choi, T. Gershon, Y. S. Lee, W. Wang, B. Shin, S.-Y. Chung. Adv. Energy Mater. 6, 1501902 (2016).
    - T. Gershon, C. Hamann, M. Hopstaken, Y. S. Lee, B. Shin, R. Haight. Adv. Energy Mater. 5, 1500922 (2015).
    - T. Gershon, B. Shin, N. Bojarczuk, M. Hopstaken, D. B. Mitzi, S. Guha. Adv. Energy Mater. 5, 1400849 (2015)
    - T. Gershon, T. Gokmen, O. Gunawan, R. Haight, S. Guha, B. Shin. MRS Comm. 4, 159 (2014).

  • Sb2Se3 Solar Cells

    Sb2Se3 is an emerging material in earth-abundant chalcogenide solar cells. Since stable chemical potential area of CZTSSe is very narrow, a quaternary CZTSSe is vulnerable to secondary phases and defects. In this regard, a binary compound Sb2Se3 recently arises as a remarkable photovoltaic material with its benign ribbon-like structure as well as its optoelectronic properties (a band gap of 1.0 – 1.2 eV and a high absorption coefficient of ~105 cm-1). Application of Sb2Se3 into the field of inorganic thin film solar cells is relatively new, and our group recently yielded a power conversion efficiency of 4.03 % using thermal co-evaporation technique. (cf. a world-record Sb2Se3 solar cell has an efficiency of 5.90 % using rapid thermal evaporation technique.) Our group aims to enhance the device performance by focusing on the interfaces and the buffer layers in Sb2Se3 solar cells.

  • SnSe Thermoelectric

    SnSe is promising thermoelectric materials because of its intrinsic low thermal conductivity originated from bonding anisotropy. Since 2014, when an article that achieved the highest thermoelectric efficiency of ZT = 2.6 with SnSe single crystals has been reported, SnSe thermoelectric device has been studied very widely. In our lab, we has been studied about the thermoelectric properties of thin-film SnSe. On this topic, we are working on collaborative research with KRISS.