Degree Granting Department
Christos S. Ferekides, Ph.D.
Don Morel, Ph.D.
Robert Mamazza, Jr., Ph.D.
Andrew M. Hoff, Ph.D.
optical properties, TCOs, front contact
Transparent conductive oxides are an essential part of technologies that require both large-area electrical contact and optical access in the visible portion of the light spectrum.
SnO2 doped with Fluorine (SnO2: F) and In2O3 doped with tin (ITO) are the most popular choices of front contacts for CdTe solar cells. In this thesis, CdS/CdTe devices were fabricated with SnO2: F (MOCVD) and ITO (sputtering) as front contacts without a high resistivity (resistivity relatively greater than front contact) buffer layer. The device characteristics of these devices were low but improved considerably after the inclusion of an intrinsic SnO2 (SnO2-i) deposited by MOCVD as buffer. Thus having emphasized and demonstrated the benefits of a buffer layer in these devices, the use of reactively sputtered SnO2 (intrinsic), SnO2 doped with Zinc (5% and 10% Zinc) and In2O3(intrinsic) as buffer layers in SnO2:F/buffer/CdS/CdTe devices were explored.
Experiments were also carried out on the photovoltaic active layers of SnO2:F/SnO2-i/CdS/CdTe Solar cells. Namely, the effect of window layer thickness was studied by making a series of devices in which the CdS thickness was progressively reduced and the effect of substrate temperature (Tsub) during the deposition of the absorber layer was also studied by increasing Tsub > 600°C during CdTe CSS.
In order to determine the effectiveness of In2O3 as a buffer layer, a series of ITO/In2O3/CdS/CdTe cells were fabricated with varying thickness of In2O3 (250 to 2000 Ǻ) and also the CdS thickness was reduced in steps (~800 Ǻ to~500 Ǻ) in these devices.
ITO/ In2O3 device with efficiency greater than 14% (Voc: 820 mV, FF: 72% and Jsc: 24 mA/cm2 ) was fabricated for an In2O3 thickness of 250 Ǻ and CdS thickness of ~ 600 Ǻ. However the best efficiency of 14.7% (Voc: 830 mV, FF: 77%, Jsc: 23 mA/cm2 ) was achieved for SnO2:F/SnO2-i/CdS/CdTe device.
ITO films with resistivity as low as 1.9X10-4 Ω-cm, mobility 32 cm2V-1s-1 and average transmission ~ 90% in the visible region were obtained for carrier concentration in the order of 1.1X1021 cm-3.
Scholar Commons Citation
Balasubramanian, Umamaheswari, "Indium Oxide as a High Resistivity Buffer Layer for CdTe/CdS Thin Film Solar Cells" (2004). USF Tampa Graduate Theses and Dissertations.