Durability of encapsulated Cu(In,Ga)Se2 solar cells using high barrier flexible front sheet under damp heat conditions testing

Cu(In,Ga)Se 2 (CIGSe) thin-film solar cells, known for their high efficiency and flexibility, are rapidly used in a variety of applications. Glass top cover encapsulation is a widely recognized method for protecting solar cells from moisture, oxygen, and mechanical stress. However, this approach increases the module's weight, and the rigidity of glass also limits the flexibility of the modules. This study investigates the long-term stability and performance of encapsulated CIGSe cells under the damp heat (DH) test as specified in the IEC 61215-2 standard. The CIGSe device was encapsulated with a lamination-based encapsulation structure using a high-barrier flexible polyethylene terephthalate (PET) front sheet and exposed to 85 o C/85% relative humidity (RH), which was carried out for 2448h. The effectiveness of forward bias voltage during the DH test was investigated by comparing two groups of cells: one group was connected with bias voltage at voltage maximum power point (Vmpp) value, and another was kept under open-circuit condition. Under both conditions, CIGSe solar cells passed the standard test by maintaining over 95% of their initial efficiency after 1000h of DH test, demonstrating the effectiveness of the encapsulation method that facilitates prolonged environmental stress. The cells with a forward bias voltage applied retained higher efficiencies with 99% and 98% of their initial efficiencies after 1008h and 2448h of the DH test, respectively. These results provide substantial information for building durable photovoltaic modules capable of withstanding harsh climatic conditions, thereby contributing to the advancement of sustainable solar energy technologies.