Characterization of W-Ti-O thin films for application in photovoltaics
Photovoltaic (PV) devices consist of the conversion of light energy into electricity. Nearly all PV technologies employ transparent conducting oxides (TCO) as an integral part of the de-vice structure so that the light can reach the semiconductor. The predominant transparent conducting oxide (TCO) that is currently being used in industry is indium tin oxide (ITO). However, Indium (In) is high in cost and becoming scarce in the world. This work is focused towards Titanium doped Tungsten oxide (WO3) for TCO application. The ultimate goal is making novel, cheaper, and efficient TCOs based on W-Ti-O films. Titanium will enhance the conductivity of the film. In addition, Ti is more abundant than In thus leading to low-cost TCO. Ti-doped WO3 (W-Ti-O) films were grown by co-sputter deposition onto silicon, Si (100), and optical grade quartz wafers. Co-sputtering of Ti and W metal targets was per-formed in a wide growth temperature range (room temperature (RT)-500 °C). The Ti sputter-ing power varied from 50 watts-100 watts in order to gain an understanding of the Ti effect. The structure and optical properties were characterized by the X-ray diffraction (XRD), scan-ning electron microscopy (SEM) and the spectrophotometry measurements. The films are op-tically transparent and a correlation between the growth conditions and optical properties is derived. The XRD results show W-Ti-O films grown at RT are amorphous and the films crys-tallize at 200°C. A decrease in the peak intensity implies that the crystallinity decreases with an increase in titanium (Ti) along with a phase change at higher substrate growth tempera-tures. The optical results show the transparency of the films is well above 80%. The energy band gap decreases from 4.0 eV to 3.9 eV with an increase in substrate temperature and in-creases from 3.85 eV to 3.95 eV with an increase of Ti. These results meet the criteria of two essential TCO parameters.
Christmas, Amanda P, "Characterization of W-Ti-O thin films for application in photovoltaics" (2014). ETD Collection for University of Texas, El Paso. AAI1564668.