Structural Properties of Ag-Based Chalcopyrite Compound Thin Films for Solar Cells
- PDF / 424,498 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 156 Views
F5.12.1
Structural Properties of Ag-Based Chalcopyrite Compound Thin Films for Solar Cells Hiroki Ishizaki, Keiichiro Yamada, Ryouta Arai, Yasuyuki Kuromiya, Yukari Masatsugu, Naoomi Yamada and Tokio Nakada Department of Electrical Engineering and Electronics, Aoyama Gakuin University, 5-10-1, Fuchinobe, Sagamihara, Kanagawa, 299-8558, Japan
ABSTRACT AgGa5Se8 and Ag(In1-xGax)Se2 thin films with different Ag/Ga atomic ratios have been deposited on the corning 1737 glass substrates by molecular beam epitaxy (MBE) system. This crystallographic property of AgGa5Se8 thin films has been investigated by x-ray diffraction and rietveld analysis. These films had the tetragonal structure with the space group of P-42m, regardless of Ag/Ga atomic ratio. The lattice parameters and the optical band gap energy decreased with an increase in the Ag/Ga atomic ratio. Thus, the structural and optical properties of these AgGa5Se8 thin films were controlled by the Ag/Ga atomic ratio.
INTRODUCTION Recently, Cu(In1-xGax)Se2 thin film solar cells have 18% efficiency [1]. In order to improve the efficiency of solar cell, a tandem solar cell and high-voltage device need to be developed. Ag(In1-xGax)Se2 presents several advantages over Cu(In1-xGax)Se2, such as (1) the band gap energy is 0.2eV wider than that of Cu(In1-xGax)Se2 [2] and (2) the melting point is 200 deg C lower than that of Cu(In1-xGax)Se2 [3]. The band gap energy of Ag(In1-xGax)Se2 film can be controlled by the Ga/ (In+Ga) atomic ratio [3,4]. Thus, the Ag(In1-xGax)Se2 solar cell will have an efficient top cell for the tandem solar cell. We have reported the influence of the Ga/(Ga+In) and Ag/(Ga+In) atomic ratios on the structural properties of Ag(In1-xGax)Se2 thin films. And high efficiency Ag(In1-xGax)Se2 solar cell with a ZnO:Al/ZnO/CBD-CdS/Ag(In1-xGax)Se2/Mo structure has been demonstrated [3]. However, other Ag-In-Ga-Se compounds existed in these Ag(In1-xGax)Se2 films. In order to improve the efficiency of Ag(In1-xGax)Se2 thin film solar cells, the structural property of this Ag-In-Ga-Se compound needed to be investigated in detail. In this paper, AgGa5Se8 thin films have been deposited on the corning 1737 glasses by the molecular beam epitaxy. The structural and optical properties of these AgGa5Se8 thin films will be discussed in detail.
EXPERIMENTAL Ag(In1-xGax)Se2 thin films were deposited by three-stages process using MBE system. For the first step, In, Ga, and Se were coevaporated at the substrate temperature of 250deg. C. And then Ag and Se were evaporated at the substrate temperature of 550deg. C. For the final step, In,
F5.12.2
Ga, and Se were coevaporated at the substrate temperature of 550deg. C to obtain the film with an excess of (In+Ga) content. The corning 1737 glasses were used as substrates. AgGa5Se8 thin films were deposited on the corning 1737 glasses by MBE system. Ag, Ga and Se were coevaporated at 550deg. C. The deposition time was 60min. The Ag/Ga flux ratio was held constant at about 5 during deposition of AgGa5Se8 thin films. And the Ag/Ga atom
Data Loading...
