Cu(In,Ga)(Se,S)2 (CIGSS) modules with a frameless glass to glass (G2G) structure were successfully fabricated by replacing the currently used ethylene vinyl acetate (EVA) with new encapsulants such as polyolefins (POE), ionomer (IO) and liquid silicon (LSI), and their characteristics including optical, mechanical, and reliability properties were investigated. Most of the solid films for encapsulation except POE exhibit similar light transmittance in the visible-infrared wavelength range, while LSI shows the highest light transmittance with a difference of more than 2% in the overall wavelength range. The G2G structure encapsulated with IO exhibits superior values for the adhesion strength at which interface failure occurs (about 7.5 MPa) compared to other encapsulants. Water vapor transmittance ratio (WVTR) values of the encapsulants were evaluated to determine their suitability as water-resistant materials in terms of the CIGSS G2G structure. The IO encapsulant had the lowest WVTR value of about 1.75 g per m2 per day. Changes of cell-to-module (CTM) conversion ratio in the CIGSS G2G structure using various encapsulants were investigated using I–V measurements. The CIGSS G2G structure encapsulated by LSI shows the best CTM conversion ratio, since the module process occurs at the lowest temperature as compared with other encapsulants, therefore the module has a smaller thermal transient effect. Finally, the long-term reliability of the CIGSS modules based on various encapsulants was also evaluated by damp heat testing.
