Tips and Tricks for a Good Encapsulation for Perovskite-Based Solar Cells

Encapsulation is a critical topic to ensure the successful implementation of perovskite photovoltaics. Recently, vacuum lamination has been shown as a promising approach that combines compatibility with current industrial processes in conventional photovoltaic (PV) manufacturing and suitability to achieve good results with perovskites. Here, we explore some of the attractive encapsulation materials in terms of their ability to prevent moisture ingress, withstand elevated temperatures, and have suitable mechanical properties to avoid thermomechanical issues. We utilized the previously suggested concept of the "perovskite test," an optical test with simple sample fabrication, for evaluating encapsulation quality and validated the findings with the full solar cell stack. Unsurprisingly, encapsulants without an edge sealant showed insufficient protection from moisture. Ionomer in combination with butyl edge seal showed the best barrier properties; however, this stack led to rapid delamination of the cell layers in thermal cycling tests. Configuration with only edge sealant does not have such an issue in principle (no mechanical stress applied), but an absence of the polymer in the stack is unfavorable in terms of optical design and sometimes showed perovskite degradation that we assign to trapped moisture in the butyl itself. Polyolefin with butyl edge sealant is not free of degradation but showed the most promising compromise by passing the damp heat test and showing fewer issues in the thermal cycling experiments. In general, our material study and optimization presented in this manuscript show that a holistic approach is needed when choosing an optimal encapsulation scheme for perovskite devices.