Effective module level encapsulation of CIGS solar cells with Al₂O₃ thin film grown by atomic layer deposition

An effective encapsulation solution for flexible CIGS is urgently needed to ensure a competitive market entry of the technology. In this work, we demonstrate the feasibility to effectively encapsulate module-level (10 × 10 cm²) CIGS/glass solar cells by employing a thin Al₂O₃ barrier layer grown by atomic layer deposition (ALD). As determined by a direct methodology, 10 nm ALD-Al₂O₃ is proved to be sufficient in preventing electrical degradation of the Al:ZnO (AZO) window layer upon exposure to damp heat test (DHT) and equally effective to encapsulate 10 × 10 cm² CIGS/glass mini-modules by efficient blockage of moisture ingress. CIGS mini-modules encapsulated by ALD-Al₂O₃ barrier layer retain an average of 80% and 72% of initial efficiency after 1000 and 2000 h of DHT, respectively. Whereas unencapsulated modules drop to an average of 67% (1000 h DHT) and 22% (2000 h DHT) of initial efficiency. Thanks to the presence of ALD-Al₂O₃ barrier layer, less electrical degradation occurred in AZO window layer and P3 interconnection; also less shunting paths appeared – both led to a lower FF drop in encapsulated CIGS mini-modules. However, an issue of Na migration out of the CIGS layer is observed, which negatively impacts the module stability during DHT.