Degree Granting Department
Christos S. Ferekides
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 lightspectrum. SnOâ doped with Fluorine (SnOâ: F) and InâOâ 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 SnOâ: 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 SnOâ (SnOâ-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 SnOâ (intrinsic), SnOâ doped with Zinc (5% and 10% Zinc) and InâOâ(intrinsic) as buffer layers in SnOâ:F/buffer/CdS/CdTe devices were explored.
Experiments were also carried out on the photovoltaic active layers of SnOâ:F/SnOâ-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 degree C during CdTe CSS. In order to determine the effectiveness of InâOâ as a buffer layer, a series of ITO/InâOâ/CdS/CdTe cells were fabricated with varying thickness of InâOâ (250 to 2000 Ǻ) and also the CdS thickness was reduced in steps (~800 Ǻ to~500 Ǻ) in these devices. ITO/ InâOâ device with efficiency greater than 14% (Voc: 820 mV, FF: 72% and Jsc: 24 mA/cmÂ²) 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/cmÂ²) was achieved for SnOâ:F/SnOâ-i/CdS/CdTe device.
ITO films with resistivity as low as 1.9X10-4 ohm-cm, mobility 32 cm2V-1s-1 and average transmission ~ 90% in the visible region were obtained for carrier concentration in the order of 1.1XE21cm-3.
Scholar Commons Citation
Balasubramanian, Umamaheswari, "Indium oxide as a high resistivity buffer layer for CdTe/CdS thin film solar cells" (2004). Graduate Theses and Dissertations.