**Abstract**

Long-term stability is a requisite for the widespread adoption and commercialization of perovskite solar cells (PSCs). Encapsulation constitutes one of the most promising ways to extend devices for lifetime without noticeably sacrificing the high power conversion efficiencies that make this technology attractive. Among encapsulation strategies, the most investigated methods are as follows: (1) glass-to-glass encapsulation, (2) polymer encapsulation, and (3) inorganic thin film encapsulation (TFE). In particular, the use of UV-, heat-, water-, and/or oxygen-resistant thin films to encapsulate PSCs is a new and promising strategy for extending devices for lifetime. Thin films can be deposited directly onto the PSC, as in TFE, or can be used in conjunction with glass-to-glass and polymer encapsulation to effectively prevent the photo-, thermal-, oxygen-, and moisture-induced degradation of the perovskite. This chapter will outline perovskite degradation mechanisms and provide a summary of the progress made to-date in the encapsulation of PSCs, with a particular focus on the most recent and promising advances that employ thin films. Additionally, the strengths and limitations of TFE approaches will be identified and contrasted against existing encapsulation strategies. Finally, possible directions for future research that can further enhance encapsulation effectiveness and extend PSC for lifetimes towards the 25-year target will be proposed.

**Keywords:** perovskite solar cells, thin film encapsulation, perovskite degradation, thin films, photovoltaics
