By Dr. Edgardo Saucedo, Catalonia Institute for Energy Research (IREC), Barcelona, Spain.
The so called kesterite (Cu2ZnSn(S,Se)4 – CZTSSe; Cu2ZnSnS4 – CZTS; Cu2ZnSnSe4 – CZTSe) has become in the last years one of the most relevant and promising emerging thin film photovoltaic technology. This family of materials share many technological aspects with the most mature chalcopyrite (Cu(In,Ga)Se2 – CIGS) compounds, which has contributed in a large extent to a fast initial progress. However, CZTSSe is considered one the most complex multinary inorganic thin film PV material developed up to now, and the researchers are currently starting to understand their peculiarities and complexities. In this sense, the low open circuit voltage (or large voltage deficit) of the solar cell devices remains as their Achilles heel. This is related to its complex structure, which includes isoelectronic Cu+ and Zn+2 atoms that can be easily exchanged in the lattice (Cu/Zn disorder), as well as the multi-valence of Sn than can adopt (+2) and (+4) oxidation states and also to form volatile species with chalcogens.
In this talk, some of the most relevant progresses of kesterite in the last years will be presented, targeting for the identification of the main possible reasons for the voltage deficit related to the complex structure of this multinary compound. The presentation will be focused in reviewing the main strategies developed until now related to the cationic and anionic substitution, including Cu by Ag, Zn by Ba, Sn by Ge and Si, as well as S, by Se and Te. The impact on the kesterite properties will be reviewed, and their potential for solving the voltage deficit problem will be discussed.
Dr. Edgardo Saucedo studied Chemical Engineering at the University of the Republic, Montevideo, Uruguay, and received his PhD in Materials Physic at the Universidad Autónoma de Madrid, Madrid, Spain in 2007. In 2007, he joined the Institut de Recherche et Développement sur l’Énergie Photovoltaïque IRDEP (Paris, France), with a CNRS associated Researcher fellowship, working in the development and optoelectronic characterization of CIGS low cost based solar cells. In 2009, he joined NEXCIS, a spin-off created from IRDEP, to further pursue their training in photovoltaic technology. Currently, he is the Deputy Head of the Solar Energy Materials and Systems Laboratory at the Catalonia Institute for Energy Research (IREC) in Barcelona, Spain. He holds four patents and has authored or co-authored more than 180 papers in recognized international journals, including: Energy and Environmental Science, Adv. Energy Materials, Journal of the American Chemical Society, Chemistry of Materials, Progress in Photovoltaics: Research and Applications, Solar Energy Materials and Solar Cells, NanoEnergy, J. Mater. Chem. A, J. Phys. Chem. C, etc. He has more than 250 contributions to the most important Congresses in Physics, Chemistry and Materials, and more than 25 invited talks around the world. He has been involved in more than 15 European and Spanish Projects (Scalenano, Inducis, Pvicokest, KestPV, Larcis, etc.), and he was the coordinator of the ITN Marie Curie network Kestcell , and he is currently the coordinator of the research and innovation H2020 project STARCELL, and the RISE (Marie Curie) project INFINITE-CELL. He is frequently chairman and invited speakers in the most relevant Conferences in Photovoltaic (E-MRS, MRS, IEEE-PVSC, EUPVSEC, European Kesterite Workshop, etc.). He has supervised nine (9) PhD Thesis and is currently supervising five (5) more. He has an h index of 30 and more than 3390 citations.