## 1 Introduction  
Laser hermetic sealing is an excellent way to protect delicate components in harsh environments for reliable packaging [1; 2]. The sealing industry has focused more attention on laser sealing as it is very effective and reliable in packaging systems, including dye-sensitized solar cells (DSSC), organic light-emitting diodes (OLEDs), solid oxide fuel cells, etc., that should be highly stable and maintain initial efficiency for more than 10 years under a harsh environment. To improve the durability of the DSSC modules, the long-term stability should be assured without electrolyte leakage after laser sealing [3; 4; 5]. Furnace-based thermal sealing and laser-assisted sealing using glass frit have been popular processes until now. In the case of laser sealing using glass frit, on one hand, glass material should show a relatively low glass transition temperature and high absorption efficiency at laser wavelength. On the other hand, the coefficient of thermal expansion between the sealing glass and the substrate should be matched to maintain high durability after sealing. However, the laser sealing process using glass frit has the disadvantage that pores are present and the sealed surface is not uniform in thickness due to evaporation of resin applied by screen printing, which cause the durability to diminish. In view of this, laser sealing using fiber types of sealant has received significant interest, owing to its ability to reduce the defect rate by improving the sealant thickness [6]. It also controls the shape to prevent the formation of internal defects, such as pores and gas, during the process. Thus, fewer pores, uniform height of the sealed surface, and low-cost sealing can be achieved using fiber types of sealant [6]. There are several requirements for materials of fiber types of sealant. In the process of glass frit, the thermal stability (\(\Delta\)T) of glass frit materials is not the main factor for the laser sealing process, but the \(\Delta\)T of fiber types of sealant needs to be 80 \({}^{\circ}\)C or more for the glass fiber to be able to be drawn to a thickness of hundreds of microns without crystallization. Further, the sealing glass material should have a low glass transition temperature and, thereby, a low thermal energy transfers to packaging devices. Moreover, the coefficient of thermal expansion (CTE) of sealing glass material should be similar to that of the panel. The CTE difference between the glass panel and sealing glass should be lower than 1.0 \(\times\) 10\({}^{-6}\) K\({}^{-1}\). In the case of laser sealing glass, it started with major compositions containing PbO in the early 1990s. However, due to environmental regulations, vanadium-based glass as a sealant has been considered a more promising candidate [7,8]. Among the candidate compositions, V2O5-P2O5-based glasses have been studied a lot in order to overcome the narrow glass-forming area of vanadium-based glass. It was reported that, when P2O5 is added into V2O5-based glass systems, the glass formation stability is improved [9,10]. However, there is a limit to its application as a sealing glass due to poor chemical durability and low water resistance [11]. Therefore, the addition of third and fourth components are required to overcome these limitations. In this work, (70-x)V2O5-5 ZnO-22 BaO-3B2O3-xM(PO3)n glass system (mol%) (where M = Al, Mg, Na, n = 3, 2, 1, respectively, mol%) was prepared by the melting and casting method. The Al(PO3)3 and Mg(PO3)2 metaphosphates were used as a source for trivalent Al2O3 and divalent MgO [12]. Incorporation of Al(PO3)3 increases the degree of structural polymerization through forming crosslinked P-O-Al bonds. The Al(PO3)3 plays a role in increasing the thermal stability and reducing the crystallization tendency in the glass network. The glass transition temperature (Tg), glass thermal stability (\(\Delta\)T), the coefficient of thermal expansion (CTE), and structural properties with respect to metaphosphate contents were determined for the purpose of fiber types of sealant.