# Progress in Improving Photovoltaics Longevity
## 4 Results
### PV Degradation Mechanisms
#### 4.1.1 Intrinsic Degradation (Internal Stress Factors)  
Intrinsic degradation [40] is related to processes that can occur even in the absence of light in the internal of the module. These internal factors include processing effects, module architectural and manufacturing techniques, and PV component compatibility. Intrinsic degradation can be addressed by selecting materials with glass transition temperatures above 100 \({}^{\circ}\)C to improve stability at functioning temperatures. * **Processing. ** One of the main causes of intrinsic degradation is poor processing, which can occur in module manufacturing or at a more fundamental level, namely in module components. Indicatively, we mention that immoderate thermal stressing of ethylene-vinyl acetate (EVA) during lamination can lead to solar cell dislocation or cracking [75]. Lamination warpage can be induced when the laminate is left to cool down to room temperature [76]. The installation of poorly crosslinked modules is also a significant factor to evaluate. For example, the utilization of poorly crosslinked EVA can increase the susceptibility toward corrosion and potential-induced degradation (PID) [77; 78] and induce full curing in operating conditions or even delamination, as it attenuates the bonding strength between EVA and all the neighboring module components [66]. * **Module architecture. ** The module architecture and design principles are considered to be of particular importance regarding the effect of intrinsic degradation. Transport and  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**PV Degradation** & **Degradation Mechanism** & **Description** & **References** \\ \hline \multirow{4}{*}{Intrinsic} & Decrease in shunt resistance (Rsh) & Due to metal migration through the p-n junction & [32; 33; 34] \\  & Antireflection coating deterioration & Reduces light absorption & [35; 36; 37; 38; 39] \\  & Hot-spot failures & Caused by mismatched, cracked, or shaded cells & [40; 41; 42] \\  & Module delamination & Caused by reductions in bond strength & [40; 43; 44] \\ \hline \multirow{4}{*}{Extrinsic} & Bubble formation in encapsulants & Leads to delamination and hot spots & [40; 45; 46] \\  & Corrosion and decreased adherence & Increases series resistance (Rs) & [47; 48; 49] \\  & to contacts & Reduces power output & [40; 43; 50; 51; 52; 53] \\  & Backsheet discoloration and cracking & \ \begin{tabular}{c} Reduces power output \\ \end{tabular}  & [40; 43; 50; 51; 52; 53] \\  & Potential-induced degradation (PID) & \begin{tabular}{c} Affects solar cell performance \\ \end{tabular}  & [40; 43; 54; 55; 56; 57; 58] \\  & Light-induced degradation (LID) & Particularly prevalent in organic photovoltaics (OPVs) & [40; 43; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101; 102;  
physical properties of packaging materials, such as oxygen, water vapor, and acetic acid transmission rates, are inseparably related to oxidation phenomena, moisture ingress, acetic acid evaporation [79], etc. The structural materials of a PV module hold a pivotal role in managing the different parameters that can contribute to degradation modes, such as oxygen, gas transmission, moisture, and water vapor [80]. For instance, in an unbreakable module construction, the choice of a packaging material with a relatively low water-vapor transmission rate may significantly restrict the moisture penetration, but it does not allow all gas-form degradation by-products to escape from the module, with all the entailed problems. Contrariwise, in a breathable module construction, a packaging material with a relatively high water-vapor transmission rate allows the uneventful movement of moisture from the unit to the environment and vice versa due to concentration gradients, which vary according to temperature's and relative humidity's seasonal and daily cycles. * **PV components compatibility**.