**3. Encapsulant structures**

The encapsulation of solar cells has been highly guided by the industrial experience with commercial silicon solar cells. In general, the components for encapsulating a solar device [22] are presented in **Figure 2**. The general requirements that each encapsulation component needs to meet in order to protect the perovskite solar cells from external degradation factors are summarized in **Table 1**. These components include:

#### **3.1 Polymeric encapsulant**

It is the most critical component (also known as pottant or filling material). The list of its requirements includes: excellent adhesion properties, optical matching for better sunlight injection, electrical insulation, mechanical support, serves to physically separate cells and strings, UV stability, mechanical strength, thermal conduction, and stands thermal cycles. In addition, the selected encapsulant needs to adapt to specific processing conditions such as narrow temperature/pressure operational ranges and restrictions about the solvents and by-products that are considered "safe" to interact with the solar cell during the encapsulation process. Typical polymeric encapsulant materials are ethylene-vinyl acetate (EVA), PVB, TPU, silicone, ionomer, and UV-curable resin. However, it is important to mention that some devices, mostly at research level, do not include a polymeric encapsulant precisely to prevent device affectation after the interaction of the solar cell with the encapsulation material. In such cases, it is common to find in the filling space a desiccant material [22]. Finally, the standard encapsulation process for commercial PV devices, for instance, silicon ones, includes two layers of encapsulant fully surrounding the solar cell and its electrical contacts.

#### **3.2 Substrate (bottom barrier)**

It provides mechanical support and must provide a good thermal conductivity and a physical barrier against weathering. Typical materials include:

**Figure 2.**

*Components used to encapsulate a perovskite solar cell.*


#### **Table 1.**

*General requirements of each encapsulation component.*

