Stephan Haass

ESR 3.2-Stephan Haass – PhD student at EMPA.

Stefan studied physics (Diplom) at the Karlsruhe Institute of Technology and during his 12 month diploma thesis investigated the surface and grain boundary properties of CIGS in collaboration with ZSW, Stuttgart. Afterwards he worked at ULVAC, Japan 6 months on the development of thin film deposition equipment for solar cell fabrication. Since August 2013 Stefan is a PhD student at Empa, Switzerland and early-stage researcher in the KESTCELLS project.

His task is the development of optimal kesterite based heterojunction solar cells, including finding suitable back contact materials, optimization of the absorber layer as well as interfaces and alternative buffer layers. Therefore many advanced skills in the field of thin film deposition and characterizations have been developed, which helped him to produce a kesterite solar cell with an efficiency of 11.2% using a solution approach.


s.G. Haass, M. Diethelm, M. Werner, B. Bissig, Y. E. Romanyuk, A. N. Tiwari, “11.2% Efficient Solution Processed Kesterite Solar Cell with a Low Voltage Deficit”, Adv. Energy Mater.Volume 5, Issue 18, September 23 (2015) DOI: 10.1002/aenm.201500712,

M. Werner, D. Keller, S. G. Haass, C. Gretener, B. Bissig, P. Fuchs, F. La Mattina, R. Erni, Y. E. Romanyuk, A. N. Tiwari, “Enhanced Carrier Collection from CdS Passivated Grains in Solution-Processed Cu2ZnSn(S,Se)4 Solar Cells”, ACS Appl. Mater. Interfaces, Jun 10;7(22):12141-6, (2015). DOI: 10.1021/acsami.5b02435

Y.E. Romanyuk, H. Hagendorfer, P. Stücheli, P. Fuchs, A.R. Uhl, C.M. Sutter-Fella, M. Werner, S. Haass, J. Stückelberger, C. Broussillou, P.-P. Grand, V. Bermudez, A.N. Tiwari, All Solution-Processed Chalcogenide Solar Cells – from Single Functional Layers Towards a 13.8% Efficient CIGS Device, Adv. Funct. Mater. 25 (2015) 12–27. doi:10.1002/adfm.201402288.

M. Neuschitzer, Y. Sanchez, S. López-Marino, H. Xie, A. Fairbrother, M. Placidi, S. Haass, V. Izquierdo-Roca, A. Perez-Rodriguez and E. Saucedo, Optimization of CdS buffer layer for high-performance Cu2ZnSnSe4 solar cells and the effects of light soaking: elimination of crossover and red kink, Progress in Photovoltaics Research and Applications, 2015. DOI: 10.1002/pip.2589

M. Neuschitzer, K. Lienau, M. Guc, L. C. Barrio, S. Haass, J. M. Prieto, Y. Sanchez, M. Espindola-Rodriguez, Y. Romanyuk, A. Perez-Rodriguez, Victor Izquierdo-Roca, E. Saucedo,”Towards high performance Cd-free CZTSe solar cells with a ZnS(O,OH) buffer layer: the influence of thiourea concentration on chemical bath deposition “, Journal of Physics D: Applied Physics,  Volume 49,  Number 12, 2016 DOI: 10.1088/0022-3727/49/12/125602

J. Marquez, M. Neuschitzer, M. Dimitrievska, R. Gunder,, S. Haass, M. Werner, Y.E. Romanyuk, S. Schorr, N.M. Pearsall, I. Forbes, “Systematic compositional changes and their influence on lattice and optoelectronic properties of Cu2ZnSnSe4 kesterite solar cells”, Solar Energy Materials and Solar Cells. (2016), Vol 144. Pp 579-585. DOI:10.1016/j.solmat.2015.10.004

B. Bissig, C. Guerra-Nunez, R. Carron, S. Nishiwaki, F. La Mattina, F. Pianezzi, P.A. Losio, E. Avancini, P. Reinhard, S.G. Haass, M. Lingg, T. Feurer, I. Utke, S. Buecheler, A.N. Tiwari, “Surface Passivation for Reliable Measurement of Bulk Electronic Properties of Heterojunction Devices, Small. (2016). DOI:10.1002/smll.201601575.


  1. M. Werner, C. M. Fella, S. Haass, Y. E. Romanyuk, A. N. Tiwari,  “Investigation of a two-solution approach for sprayed kesterite films for solar cells”. Kesterite Meeting 2013, HZB, Berlin. (Poster)
  2. J.Márquez, M. Neuschitzer, S. Haass, M. Werner, Y. Romanyuk and I. Forbes . Influence of the Cu Content on CZTSe Thin Film Solar Cells . 5th European Kesterite Workshop. Tallin, Estonia. 2014. (Oral).
  3. J. Márquez, M. Neuschitzer, M. Dimitrievska, S. Haass, M. Werner, Y.E. Romanyuk, N. Pearsall and I. Forbes”Influence of the Cu Content on Sputtered CZTSe Thin Film Solar Cells. Presented atMRS-Spring Meeting.  San Francisco, USA. (Poster)
  4. M.Neuschitzer, K.Lienau, S.Haass, J. Marquez Prieto, Y.Sanchez, YE Romanyuk, A.Perez-Rodriguez, E.Saucedo Silva. “Towards high performance Cd-free CZTSe solar cells with ZnS(O,OH) buffer layer: The influence of the thiourea concentration during CBD” MRS Spring Meeting 2015, San Francisco, USA
  5. Stefan G. Haaß, Carolin M. Sutter, Yaroslav E. Romanyuk, Ayodhya N. Tiwari. Selenization of solution-deposited CZTS precursors under controlled Se overpressure in evacuated glass ampules. In: EMRS spring meeting 2014. Lille, France, 2014. (Poster).
  6. S. G.Haass, M. Werner, M. Diethelm, Y. E. Romanyuk, A. N. Tiwari, “Advanced characterization and defect analysis of high efficient solution deposited Cu2ZnSn(S,Se)4 solar cells”, EU-PVSEC 2015, Hamburg (Germany), 2015. (oral)
  7. S. G. Haass, M. Diethelm, C. Andres, Y. E. Romanyuk, A. N. Tiwari, “Potassium treatment of solution-processed kesterite solar cells”, Kesterite Workshop 2015, NU, Newcastle (UK). (oral)
  8. S. G. Haass, M. Diethelm, C. Andres, Y. E. Romanyuk, A. N. Tiwari, ”Potassium treatment strategies for solution-processed kesterite solar cells”, E-MRS Spring Meeting 2016, Lille (France), 2016. (Oral)