High-efficiency polycrystalline CdTe thin-film solar cells with an oxygenated amorphous cds (a-CdS:O) window layer

Author

Wu, X. ; Dhere, R.G. ; Yan, Y. ; Romero, M.J. ; Zhang, Y. ; Zhou, J. ; DeHart, C. ; Duda, A. ; Perkins, C. ; To, B.

Author_Institution

Nat. Renewable Energy Lab., Golden, CO, USA

fYear

2002

fDate

19-24 May 2002

Firstpage

531

Lastpage

534

Abstract

In the conventional CdS/CdTe device structure, the poly-CdS window layer has a bandgap of ∼2.4 eV, which causes absorption in the short-wavelength region. Higher short-circuit current densities (J_sc) can be achieved by reducing the CdS thickness, but this can adversely impact device open-circuit voltage (V_oc) and fill factor (FF). Also, poly-CdS film has about 10% lattice mismatch related to the CdTe film, which limits the improvement of device V_oc and FF. In this paper, we report a novel window material: oxygenated amorphous CdS film (a-CdS:O) prepared at room temperature by rf sputtering. The a-CdS:O film has a higher optical bandgap (2.5-3.1 eV) than the poly-CdS film and an amorphous structure. The preliminary device results have demonstrated that J_sc of the CdTe device can be greatly improved while maintaining higher V_oc and FF. We have fabricated a CdTe cell demonstrating an NREL-confirmed J_sc of 25.85 mA/cm² and a total-area efficiency of 15.4%.

Keywords

II-VI semiconductors; Raman spectra; amorphous semiconductors; cadmium compounds; energy gap; noncrystalline structure; optical windows; oxygen; photoconductivity; semiconductor thin films; solar cells; sputtered coatings; 15.4 percent; 2.5 to 3.1 eV; CdS thickness; CdS-CdTe; CdS:O; CdTe; a-CdS:O; absorption; amorphous structure; bandgap; conventional CdS/CdTe device structure; device open-circuit voltage; fill factor; high-efficiency polycrystalline CdTe thin-film solar cells; higher optical bandgap; higher short-circuit current densities; lattice mismatch; oxygenated amorphous CdS window layer; poly-CdS film; poly-CdS window layer; rf sputtering; room temperature; short-wavelength region; total-area efficiency; Absorption; Amorphous materials; Current density; Lattices; Optical films; Optical materials; Photonic band gap; Photovoltaic cells; Transistors; Voltage;

fLanguage

English

Publisher

ieee

Conference_Titel

Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE

ISSN

1060-8371

Print_ISBN

0-7803-7471-1

Type

conf

DOI

10.1109/PVSC.2002.1190619

Filename

1190619