Západočeská univerzita v Plzni , Česká republika Výzkumné centrum Nové technologie

1. Západočeská univerzita v Plzni, Česká republika Výzkumné centrum Nové technologie STUDIUM ZMĚNY OPTICKÝCH VLASTNOSTÍ V ZÁVISLOSTI NA ZMĚNĚ STRUKTURY a-Si:H Lucie Prušáková, Veronika Vavruňková, Marie Netrvalová, Jarmila Mullerová, Pavol Šutta Váš partner pro výzkum, vývoj a inovace v průmyslových aplikacích This presentation is co-financed by the European Social Fund and the state budget of the Czech Republic.

2. Materiály a technologie (MAT) projekt 1M06031 Materiály a komponenty pro ochranu životního prostředí University of West Bohemia – New Technologies Research Centre

3. Introduction : • Tandem solar cell is one of the concepts well established as a way how to improve solar cell performance beyond that of a single cell. • This concept needs semiconductor materials with different band-gaps, which are stacked on top of another, in order to filter the photons of different energies passing through the stack. • One of the possibilities how to solve this problem is taking advantage from the well established silicon technology (a-Si:H, μc-Si:H and poly-Si materials). University of West Bohemia – New Technologies Research Centre

4. Introduction : • One of the possibilities how to obtain poly-Si films of a good quality consists generally of two steps: • Deposition of a-Si or a-Si:H thin films by means of PVD or CVD technologies at low temperatures and • Subsequent re-crystallization of the films from solid phase by thermaltreatment at temperatures near to 600°C. University of West Bohemia – New Technologies Research Centre

5. Deposition technique: PE-CVD SAMCO PD 220N unit • deposition temperature 250°C • RF power 40 W • at constant presure of 67 Pa • Precursors: SiH4 (10% in Ar), H2 University of West Bohemia – New Technologies Research Centre

6. Outline of the experiment: R = [H ] / [SiH ] 4 University of West Bohemia – New Technologies Research Centre 2

7. XRD: Panalytical X’Pert PROX-ray powder diffractometer • Applications: • Qualitative and quantitative phase analysis • Residual stress analysis • Texture analysis • Analysis of changes in the crystal structure • Ultra fast data collection with using X’Celerator Theta-Theta goniometer University of West Bohemia – New Technologies Research Centre Substrate: Corning glass Deposition temperature: 250 °C Dilution: R = 0, 20, 30, 40, 50 (R = H2/SiH4) Working gas: Argon (90 %) / silane (10 %) XRD patterns - in range of 15 – 65 degrees of 2 measured on attachment *)with asymmetric geometry - semi-quantitative XRD phase analysis was carried out from all significant diffraction lines

8. XRD: University of West Bohemia – New Technologies Research Centre

9. XRD: University of West Bohemia – New Technologies Research Centre

10. XRD: University of West Bohemia – New Technologies Research Centre

11. Raman spectroscopy: Yvon Labram Raman Spectrometer Micro-Raman spectra excited with a laser generating the wavelength of 532 nm Shift of the Raman peaks due to different hydrogen dilution was observed University of West Bohemia – New Technologies Research Centre

12. Influence of hydrogen : University of West Bohemia – New Technologies Research Centre

13. Optical spectrophotometry: • Spectral refractive indices and absorbtion coefficients were extracted from measured transmittance spectra using the Delphi-based program based on an optimization procedure using genetic algorithm • The optimization procedure minimizes differences between the experimental and theoretical transmittance i the broad spectral region including the region in the vicinity of the absorption edge. SPECORD210 • UV / VIS Spectrophotometer • spectral region 190 – 1100 nm • measurement of transmittance, absorbance and reflectance in dependence on the wavelength • Accessories • Absolute Reflectance Attachment (determine the absolute reflectance of reflecting films) • Variable Angle Reflectance Attachment (determine refractive index of solid samples) • Integrating Sphere (for the measurement of transmittance and diffuse reflectance) University of West Bohemia – New Technologies Research Centre

14. Optical properties: The refractive index shifts towards the values typical for single-crystalline silicon (n ~ 3.5) with increasing R. Increased hydrogen dilution shifts the absorption edge to the higher energies (lower wavelengths). The optical band-gap energies for the films with lower hydrogen dilution (R≤20) are 1.75 - 1.9 event. In case of R≥30 Eg = 2.15 eV. University of West Bohemia – New Technologies Research Centre

15. Outline of the experiment: University of West Bohemia – New Technologies Research Centre Substrate: Corning glass Deposition temperature: 250 °C Dilution: R = 0 (R = H2/SiH4) Working gas: Argon (90 %) / silane (10 %) Isothermal heating was used Linear temperature starting-up (50°C/min.) was applied Pressure in a high-temperature chamber was 0.1 Pa Temperature decay - exponential shape (only by irradiation) XRD patterns– in range of 15 – 65 degrees of 2 in initial state measured on attachment *) – lines (111) during the heating – in range of 20 – 65 degrees of 2 after the heat treatment

16. Outline of the experiment: „In situ“ XRD monitoring of a-Si:H poly-Si re-crystallization process Parameters of the experiment University of West Bohemia – New Technologies Research Centre

17. X-ray diffraction – symmetric - geometry : University of West Bohemia – New Technologies Research Centre

18. Raman spectroscopy : University of West Bohemia – New Technologies Research Centre

19. Refractive indices : 600 nm 1200 nm 1860 nm 2400 nm University of West Bohemia – New Technologies Research Centre

20. UV-VIS spectrophotometry : 600 nm 1200 nm 1860 nm 2400 nm University of West Bohemia – New Technologies Research Centre

21. Absorption coeficient : 1200 nm 600 nm 1860 nm 2400 nm University of West Bohemia – New Technologies Research Centre

22. Absorption coeficient : 1200 nm 600 nm 1860 nm 2400 nm University of West Bohemia – New Technologies Research Centre

23. Absorption coeficient : Our results Comparison University of West Bohemia – New Technologies Research Centre A.V.Shah et al., Progress in Photovoltaics: Research and Applications, 2004, 12, 113 – 142

24. Conclusions : • Amorphous and polycrystalline silicon films were obtained using PE-CVD. Amorphous phase a-Si:H - R≤20; polycrystalline c-Si:H - R≥30. • Polycrystalline silicon films were obtained using subsequent thermal processing of the films at temperatures near 600°C. • PE-CVD / re-crystallized poly-Si films still containing 30-50/ 21-25% residual amorphous (disordered) phase, which was confirmed by the Raman spectroscopy. • Average crystallite size obtained from the PE-CVD / re-crystallization process was 15-20 / 40-50 nm without particular dependence on heat treatment temperature used. • Significant optical absorption in re-crystallized siliconfilms compared with a-Si:Hwas observed between 1.65 – 1.85 eV photon energies. • These results indicate that the films under study could be considered as convenient material for tandem solar cells technologies. University of West Bohemia – New Technologies Research Centre

25. Pilsner TCO´s : • All samples – polycrystalline structure • Crystallite size – 68 to 109 nm 0,0046 Ω.cm • Low resistivity – • High transparency - • High reproducibility of sputtering process • Dependence of Resistivity on Biaxial stress • Texture in [001] direction perpendicular to the substrate > 90% University of West Bohemia – New Technologies Research Centre Standard - ZnO powder XRD patterns for sputtered ZnO:Al films

26. Acknowledgements : • Efficiency 9.97% - ASAHI • Efficiency 6.89% - AZO 4 University of West Bohemia – New Technologies Research Centre

27. Acknowledgements : This work was supported by the project of MSMT of the Czech Republic No. 1M06031 and by the Slovak Grant Agency under the project No. 2/0070/10 and by the Slovak Research and Development Agency under the project APVV-0577-07. The authors would like to thank to M. Ledinsky from CAS for Raman spectra measurements. University of West Bohemia – New Technologies Research Centre

28. Thank you for Your interest in photovoltaic applications