## 1 Introduction  
Molybdenum (Mo) thin films have received considerable attention for various applications such as protective coatings, source/drain electrodes, integrated circuits and solar cells, due to their high thermal and chemical stability, high electrical conductivity and resistance to corrosion [1; 2; 3; 4; 5]. Magnetron sputtering is the most commonly used method for the preparation of Mo films originating from several advantages such as low cost, easy to adjust the parameters, films can be deposited uniformly on large-sized areas [6]. A large number of studies have shown that the structures and properties of Mo films are related to the preparation process and parameters [7; 8; 9]. For instance, [PERSON] et al., [10] investigated the effects of deposition pressures and powers on the structures and photoelectric properties of Mo films prepared by radio frequency (RF) magnetron sputtering. [PERSON] et al., [11] reported the effects of the sputtering powers and sputtering pressures on the Mo films deposited using direct current (DC) magnetron sputtering. The results clearly indicated that the sputtering powers, sputtering pressures and temperatures had significant influences on grain sizes, optical and electrical properties of Mo thin films prepared by either RF or DC magnetron sputtering. Generally, it is very difficult for Mo thin films to possess low electrical resistivity and good adhesion to the substrate, simultaneously. Specifically, films deposited at lower sputtering pressure have lower electrical resistivity but poor adhesion, whereas those deposited at higher sputtering pressure have better adhesion but higher electrical resistivity. To solve the problem, [PERSON] et al., [12] designed a Mo bilayer film, which consisted of a bottom layer deposited at higher sputtering pressure for better adhesion and a top layer deposited at lower sputtering pressure for better conductivity. Since then, many researchers have begun to focus on the effects of processing parameters on structures and properties of the Mo bilayer films prepared by RF/RF and/or DC/DC magnetron sputtering. In the work of [PERSON] et al., [13] the Mo bilayer films prepared by DC/DC magnetron sputtering were optimized. The results indicated that the copper indium gallium selenium (CIGS) solar cell had the maximum photo-conversion efficiency of 12.83%. [PERSON] et al., [14] investigated the effects of sputtering powers and argon gas flow rates on the properties of Mo bilayer films prepared by DC/DC magnetron sputtering. The results showed that better crystallinity, reflectance and electrical conductivity were obtained at higher sputtering power and lower argon gas flow rate. [PERSON] et al. [15] studied the properties of Mo bilayer films prepared by RF/RF and DC/DC sputtering modes, demonstrating that a high efficiency of CIGS thin films solar cell was achieved to be 16.2%. However, fewer people focused on the influences of processing parameters on the properties of Mo bilayer films prepared by RF/DC sputtering method. Commonly, Mo films prepared by RF sputtering have better adhesion to the substrate and higher reflectance but lower conductivity than those prepared by DC sputtering under the same sputtering conditions, but the Mo films prepared by DC sputtering have better conductivity [16]. Actually, the reflectance of Mo back electrode is also very important to the Cu(In,Ga)Se\({}_{2}\) (CIGS), copper zinc tin sulphur (CZTS) and other solar cells, because higher reflectance can improve their photo-conversion efficiency [17]. In this paper, we prepared a new Mo bilayer film. The bottom layer was deposited by RF sputtering to ensure better adhesion to the substrate and higher reflectance, and the top layer was deposited by DC sputtering to ensure better electrical conductivity. It is known that the performance of the films will change with the changes of process parameters in the Mo bilayer films prepared by DC/DC sputtering mode.