1. Západočeská univerzita v Plzni, Česká republika Výzkumné centrum Nové technologie Váš partner pro výzkum, vývoj a inovace v průmyslových aplikacích STUDIUM ZMĚNY OPTICKÝCH VLASTNOSTÍ V ZÁVISLOSTI NA ZMĚNĚ STRUKTURY a-Si:H Marie Netrvalová, Jarmila Mullerová, Pavol Šutta Lucie Prušáková, Veronika Vavruňková, 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 technologies at low temperatures and  Subsequent re-crystallization of the films from solid phase by thermal treatment 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: DilutionSiH + Ar flow [sccm] H flow [sccm] Volume content [%]Dimension of coherently diffracting domain [nm] Thickness [nm] SiliconSilicon hydride SiliconSilicon hydride R 02500----170 R 2083167----120 R 3062.5187.5----140 R 40502005347618140 R 50422083268914180 University of West Bohemia – New Technologies Research Centre 2 R = [H ] / [SiH ] 4

7. XRD: Panalytical X’Pert PRO X-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 = H 2 /SiH 4 ) 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: University of West Bohemia – New Technologies Research Centre 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

12. Influence of hydrogen : DilutionVolume content [%]Dimension of coherently diffracting domain [nm] Thickness [nm] SiliconSilicon hydride SiliconSilicon hydride R 405347186140 R 506832149180 University of West Bohemia – New Technologies Research Centre

13. Optical spectrophotometry: University of West Bohemia – New Technologies Research Centre 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) SPECORD 210 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.

14. Optical properties: University of West Bohemia – New Technologies Research Centre 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.

15. Outline of the experiment: Series number Thickness [nm] Re-crystallization temperature [°C] Comments 123456 580590600610620ref. A0035240042 2218 1*1* The thicknesses of the samples were evaluated from the optimization procedure during the optical spectra processing A0036186042 2218 1*1* A0037120042 2218 1*1* A0038600-422218 1*1* -Σ =126168872 4*4*ΣΣ = 530 XRD records University of West Bohemia – New Technologies Research Centre Substrate:Corning glass Deposition temperature:250 °C Dilution:R = 0(R = H 2 /SiH 4 ) 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: University of West Bohemia – New Technologies Research Centre „In situ“ XRD monitoring of a-Si:H poly-Si re-crystallization process Parameters of the experiment Sample number Temperature Number of XRD measurements Duration [hours] 1580°C40+220 2590°C40+220 3600°C20+210 4610°C16+28 5620°C16+28 6roombefore-

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 : 1860 nm 600 nm1200 nm 2400 nm University of West Bohemia – New Technologies Research Centre

20. UV-VIS spectrophotometry : 600 nm 1200 nm 2400 nm1860 nm University of West Bohemia – New Technologies Research Centre

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

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

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

24. Conclusions : University of West Bohemia – New Technologies Research Centre Amorphous and polycrystalline silicon films were obtained using PE- CVD. Amorphous phase a-Si:H - R≤20; polycrystalline  c-Si:H - R≥30.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.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.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.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 silicon films compared with a-Si:H was observed between 1.65 – 1.85 eV photon energies.Significant optical absorption in re-crystallized silicon films compared with a-Si:H was 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.These results indicate that the films under study could be considered as convenient material for tandem solar cells technologies.

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

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

27. Acknowledgements : University of West Bohemia – New Technologies Research Centre 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.

28. Thank you for Your interest in photovoltaic applications