Thomas Kirchartz

Advanced Characterization Techniques for Thin Film Solar Cells

I Introduction 1. Introduction to thin-film photovoltaics II Device characterization 2. Fundamental electrical characterization of thin-film solar cells 3. Electroluminescence analysis of thin-film solar modules 4. Capacitance spectroscopy of thin-film solar cells III Materials characterization 5. Characterizing the light trapping properties of textured surfaces with scanning near-field optical microscopy 6. Ellipsometry 7. Photoluminescence analysis of Si and chalcopyrite-type thin films for solar cells 8. Steady state photocarrier grating method 9. Time-of-flight analysis 10. Electron Spin Resonance on Si thin films for solar cells 11. Scanning probe microscopy on thin films for solar cells 12. Electron microscopy on thin films for solar cells 13. X-ray and neutron diffraction of materials for thin film solar cells 14. Raman Spectroscopy on thin films for solar cells 15. Soft x-ray and electron spectroscopy: a unique tool chest to characterize the chemical and electronic properties of surfaces and interfaces 16. Elemental distribution profiling of thin films for solar cells 17. Hydrogen effusion experiments IV Materials and device modelling 18. Ab-initio modelling of semiconductors 19. One-dimensional electro-optical simulations of thin film solar cells 20. Two-dimensional electrical simulations of thin film solar cells

Electroluminescence from Cu(In,Ga)Se 2 Thin-film Solar Cells

We compare the electroluminescence (EL) of three polycrystalline ZnO/CdS/Cu(In,Ga)Se 2 heterojunction solar cells with similar bandgaps but different open circuit voltages, indicating a difference in the electronic quality of the absorber. Temperature dependent electroluminescence measurements reveal that all cells feature transitions from donor-acceptor pair recombination at lower temperatures to band to band recombination at higher temperatures. However, the less efficient cells show a longer transition range with donor-acceptor pair recombination still apparent at room temperature. The thus broadened room temperature luminescence is one effect which reduces the open circuit voltage of the devices below the Shockley-Queisser-limit. The other effect is the existence of non-radiative recombination currents, which determine the efficiency of the device as light emitting diode. To quantify the open circuit voltage losses, we use reciprocity relations between electroluminescent and photovoltaic action of solar cells, which allow us to predict the light emitting diode efficiency. Measurements support the theory and show that Cu(In,Ga)Se 2 solar cells reach external LED efficiencies approaching.