High Haze and Low Resistive MgO/AZO Bi-layer Transparent Conducting Oxide for Thin Film Solar Cells
- PDF / 933,104 Bytes
- 6 Pages / 595.22 x 842 pts (A4) Page_size
- 5 Downloads / 154 Views
High Haze and Low Resistive MgO/AZO Bi-layer Transparent Conducting Oxide for Thin Film Solar Cells Dong Won Kang1, Jong Seok Woo1, Sung Hwan Choi1, Seung Yoon Lee2, Heon Min. Lee2, and Min Koo. Han1 1 2
Electrical Engineering, Seoul National University, Seoul, 151-742, Republic of Korea Solar Energy group, LG Electronics, Seoul, 137-724, Republic of Korea
ABSTRACT We have propsed MgO/AZO bi-layer transparent conducting oxide (TCO) for thin film solar cells. From XRD analysis, it was observed that the full width at half maximum of AZO decreased when it was grown on MgO precursor. The Hall mobility of MgO/AZO bi-layer was 17.5cm2/Vs, whereas that of AZO was 20.8cm2/Vs. These indicated that the crystallinity of AZO decreased by employing MgO precursor. However, the haze (=total diffusive transmittance/total transmittance) characteristics of highly crystalline AZO was significantly improved by MgO precursor. The average haze in the visible region increased from 14.3 to 48.2%, and that in the NIR region increased from 6.3 to 18.9%. The reflectance of microcrystalline silicon solar cell was decreased and external quantum efficiency was significantly improved by applying MgO/AZO bi-layer TCO. The efficiency of microcrystalline silicon solar cell with MgO/AZO bi-layer front TCO was 6.66%, whereas the efficiency of one with AZO single TCO was 5.19%. INTRODUCTION Al-doped ZnO (AZO) has been widely used as front transparent conducting oxide (TCO) for thin film solar cells in terms of high transparency and low resistivity [1-2]. Haze (=total diffusion/total transmission) property of surface textured AZO is also an important factor for characterizing light trapping ability. The improvement of those AZO properties is crucial for solar cell efficiency. It was reported that the crystallinity of ZnO was improved by MgO buffer layer on sapphire substrate [3]. However, the sapphire substrate is not suitable for thin film solar cells employing low cost glass substrate. In addition, the optoelectronic properties of MgO/AZO bi-layer deposited on glass substrate for thin film solar cell applications were not reported yet. Thus, the purpose of our paper is to report the effect of MgO precursor on film crystallinity and haze properties of AZO film. The structural, electrical, and optical properties of MgO/AZO bi-layer TCO have been systemically investigated. In addition, the performance of thin film solar cell employing MgO/AZO bi-layer front TCO, forming the solar cell structure of (glass/MgO/AZO/microcrystalline silicon p-i-n/AZO/Ag/Al), have been investigated. EXPERIMENT MgO and AZO films were prepared by magnetron sputtering. The 4-inch ceramic targets consisted of AZO (2wt.% Al2O3) and MgO (4N) were used. Prior to deposit thin films, 5 min
pre-sputtering was performed to eliminate possible contaminants on the targets and base pressure under 1.0×10-6 Torr was maintained by cryo-pump (GENESIS ICP-150). At first, reference AZO film of about 1µm was prepared on glass substrates (Corning) at the substrate temperature of 250oC, working
Data Loading...
