Research presented at Symposium P of the 10^th International Conference of Materials and Advanced Technology (ICMAT 2019)

Abstract

Discovery and development of affordable renewable energy sources is of paramount importance for the continuous growth of human civilization while minimizing global warming. Converting solar energy to electricity or fuel presents a golden opportunity towards truly accessible, low cost and clean source of energy. Thin film inorganic materials may open up new opportunities in flexible solar cells, wearable technologies and building integrated photovoltaics (BIPV) beyond the traditional (silicon-based) solar panels installed on roof tops and solar farms. Conversion of sunlight into useful chemicals such as O₂ and H₂, enabled by photo(electro)chemical reactions of semiconductor photoelectrodes, also presents a promising opportunity to harvest solar energy. Towards this, we present a collection of selected articles on the recent development of chalcogenide based inorganic materials for solar energy harvesting which were presented at symposium P of the 10th International Conference of Materials and Advanced Technology (ICMAT2019) hosted by MRS-Singapore.

Goutam Kumar Dalapati

Goutam Kumar Dalapati is an associate professor in the Department of Physics at SRM University-Amaravati, AP, India and also associated with Center for Nanofibers and Nanotechnology, Faculty of Engineering, National University of Singapore, Singapore. His research works focus on the development of prototype (solar cells and heat mirror) using earth abundant and non-toxic materials. His key research interests and current industrial engagements are in the areas of thin film technology, energy saving smart coating, solar cells, and accelerated materials development through machine learning. Dr Dalapati is working on copper oxides based photocathode for large area solar hydrogen generation and chalcogenides based thin film solar cells. During 2016–2018, Dr Dalapati was an associate editor for Scientific Reports (Nature publishing group). He also served guest editors for solar energy materials and solar cells (SOLMAT, Elsevier), and Journal of Materials Chemistry A (JMCA, RSC).

Lydia Helena Wong

Lydia Helena Wong is an Associate Professor at the School of Materials Science and Engineering, Nanyang Technological University (NTU), Singapore and served as Assistant Chair (Student) in 2015–2018. Her research area include solution based synthesis of thin film and nanostructured metal oxides and chalcogenides, photovoltaic devices, (photo)electrochemical devices for solar to fuel conversion and accelerated discovery of new materials using high throughput synthesis and characterization methods. To date she has published more than 100 publications (including reviews and book chapter) in international peer reviewed journals. Lydia has served as editor for Journal of Materials Science: Materials in Electronics in 2017–2019 and guest editor for Journal of Materials Chemistry A (JMCA, RSC).

Frank Erich Osterloh

Frank Osterloh is an inorganic chemist working on the construction of particle-based devices for photocatalytic water splitting and on the application of surface photovoltage spectroscopy for the observation of photochemical charge transfer. Since joining the faculty at the Chemistry Department at the University of California, Davis in 2000, Frank has authored over 100 scientific papers, incl. several review articles and book chapters. His research contributions were recognized with the 2010 ACS Inorganic Nanoscience award and the 2014 Richard A. Glenn Award of the ACS (Division of Fuel Chemistry). In 2016, he was named Fellow of the Royal Society of Chemistry. He currently serves as associate editor for the ‘Journal of Materials Chemistry A’, published by the RSC, and on the editorial advisory board of ChemNanoMat (Wiley-VCH).

Among different inorganic materials, copper based materials have the potential to bring game changing solutions to the current industrial challenges related to energy production (solar cells, fuel cells), electrical energy storage (super-capacitors, batteries) and hydrogen storage. Copper kesterites based semiconductors such as copper-zinc-tin-sulphide (Cu₂ZnSnS₄, CZTS), copper-zinc-tin-selenide (Cu₂ZnSnSe₄, CZTSe) and copper-zinc-tin-sulpho-selenide (Cu₂ZnSn(S,Se)₄, CZTSSe) materials show exciting optical characteristics with significant potential for photovoltaic devices.^1,2 They are easy to synthesise and can be integrated into flexible materials to be utilised for building integrated photovoltaic (BIPV) applications. Despite the sustainability and earth abundancy, the development of kesterite based solar cells are hindered by, among other things, (i) unoptimized interfaces, and (ii) presence of deep and shallow defects in the absorber.^3,4 While the origins of the deep defects are presently still debatable, many have attributed this to the Cu–Zn, Cu–Sn and Zn–Sn antisites which prompted significant efforts to substitute Cu, Zn, Sn with other cations.⁵ In this collection, two of the most successful substitutes, Ag and Cd, were reported to have beneficial effect on monograin CZTS solar cells (DOI: 10.1039/c9ta07768e). The reason behind the superior performance of Cd-substituted CZTS is further elucidated by a combination of computational and structural characterizations, which reveal the effect of Cd on the cation redistribution in Cu₂(Zn,Cd)SnS₄ and show that Cu₂CdSnS₄ has less structural disorder than Cu₂ZnSnS₄ (DOI: 10.1039/c9ta09572a). Efforts to improve the performance by modifying the CZTS/ZnCdS interface is reported to achieve power conversion efficiency over 10% (DOI: 10.1039/c9ta09576d), while a flexible CZTSSe solar cells with power conversion efficiency of ∼10% was reported by implementing an oxide based diffusion barrier on stainless steel substrate (DOI: 10.1039/c9ta08265d). Lastly, we would also highlight a potential emerging binary chalcogenide, antimony sulfo-selenide (Sb₂(S,Se)₃), whose efficiency is approaching 10% (a review of record efficiency cells of this family of material is provided in ref. 6). One important prerequisite for the high efficiency of Sb₂(S,Se)₃ is the preferential growth in hk1 direction which is investigated carefully by Park et al. in this collection (DOI: 10.1039/c9ta08289a), while Yang and Moon provided a recent highlight of the use of Sb₂Se₃ as photocathode for solar to hydrogen generation (DOI: 10.1039/c9ta07990d).

Finally, we thank all contributing authors and reviewers of this themed collection, as well as Dr Christopher Dias (Publishing Editor) and Lynn Murphy (Deputy Editor) of the RSC whose assistance was invaluable to realize this themed collection.

References

1. M. T. Winkler, et al., Optical designs that improve the efficiency of Cu₂ZnSn(S, Se)₄ solar cells, Energy Environ. Sci., 2014, 7, 1029–1036.
2. C. Yan, et al., Cu₂ZnSnS₄ solar cells with over 10% power conversion efficiency enabled by heterojunction heat treatment, Nat. Energy, 2018, 3, 764–772.
3. M. Kumar, et al., Strategic review of secondary phases, defects and defect-complexes in kesterite CZTS–Se solar cells, Energy Environ. Sci., 2015, 8, 3134.
4. S. Zhuk, et al., Critical review on sputter-deposited Cu₂ZnSnS₄ (CZTS) based thin film photovoltaic technology focusing on device architecture and absorber quality on the solar cells performance, Sol. Energy Mater. Sol. Cells, 2017, 171, 239.
5. Y. E. Romanyuk, et al., Doping and alloying of kesterites, Journal of Physics: Energy, 2019, 1, 044004.
6. L. H. Wong, et al., Emerging inorganic solar cell efficiency tables (Version 1), Journal of Physics: Energy, 2019, 1, 032001.

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