By Dr. Teodor Todorov, IBM T. J. Watson Research Center, Yorktown Heights, USA.
Thin-film multinary chalcogenide absorbers have numerous attractive properties such as tunable direct band gap, high absorption coefficient and stability which are advantageous for large-scale standalone or tandem device applications. The most thoroughly optimized of these materials, Cu(In,Ga)(S,Se)2 or CIGS, has already reached efficiencies beyond 21%, and entered gigawatt-scale manufacturing. In order to mitigate the reliance on strategic rare earth elements such as indium, earth-abundant materials including CZTS (Cu2ZnSn(S,Se)4) have attracted significant research interest. We present an overview of our work leading to World-record Cu2ZnSn(S,Se)4 solar cells and analyze the challenges that need to be addressed in order to reach the competitive performance levels for industrial transfer of these materials.
Teodor Todorov completed his PhD in Materials Science at the Jaume-I University (Spain). He has always been attracted to low-cost and scalable solar energy technologies and explored different non-vacuum routes for PV films at Hahn-Meitner Institut (now Helmhotz-Zentrum, Berlin), IRDEP (l’Institut de Recherche et Développement sur l’Énergie Photovoltaïque, Paris) and IEC (Institute of Energy Conversion, Delaware). In 2008 he joined IBM T. J. Watson Research Center where his World-record results with CZTSSe photovoltaic technology motivated the launch of many research projects at the company and around the globe. He invented numerous thin film device structures, methods and processing equipment that lead to more record results including CZTSSe, solution-processed CIGS and the first monolithic tandem perovskite solar cells on chalcogenide bottom devices. Recently he achieved a new record with the oldest photovoltaic material – selenium with attractive high band gap and voltage for tandem, wearable and IOT applications. He is currently expanding the area of his research towards other thin-film materials and devices for energy and novel computing applications.