Optical and structural characteristics of quaternary semiconductor thin films for photovoltaic applications

The need for energy has been increasing day by day in the world. Fossil fuels which are used to eliminate the need, are both depleted and cause environmental disasters. In this respect, solar energy among renewable energies is the most important candidate for energy resource. In recent years, studies on this issue have been very important and exciting. Kesterite phase of Cu2ZnSnS4 (CZTS) occurs in the nature and is the most likely alternative to Cu(In,Ga)Se2 (CIGS) thin film solar cells which started to spread increasingly in all over the world. CZTS is very suitable absorber layer material for thin film solar cells due to containing cheap material, has a 1.5 eV band gap that is the most appropriate for theoretical Shockley-Queisser limit values and the large absorption coefficient (104 cm-1). Cu2CdSnS4 (CCTS) is a semiconductor with a band gap of 1.37 eV and has a large absorption coefficient over 104 cm−1 which makes it a possible photovoltaic material. Its structure is similar to CZTS. In this work, cheap and abundant material containing Cu2CdSnS4 (CCTS) and Cu2ZnSnS4 (CZTS) starting to find its place in solar cell production, quaternary semiconductor films were produced on glass substrates by ultrasonic spray pyrolysis method. The structural features of the thin films were determined by X-ray diffraction (XRD), the molecular structure by Raman spectroscopy, surface morphology by Scanning Electron Microscopy (SEM). Light transmittance and absorbance of the films were used for determining of absorption properties by UV-VIS-NIR as absorber layers in photovoltaic applications. Optical band gaps of the films were determined. Important electrical parameters of solar cells such as charge carrier density, conductivity type and resistivity were measured by Hall effect measurement system. Solar cells were fabricated by using most appropriate thin films according to optical and electrical properties.