# Progress in Improving Photovoltaics Longevity
## 4 Results
### PV Degradation Mechanisms
#### 4.1.2 Extrinsic Degradation (External Stress Factors)
Thermal leakage can also occur when the heat dissipation mechanism is not successful, and the non-countered high temperature will eventually cause cessation of the diode operation. Furthermore, an open circuit failure can arise in the case of a damaged or disconnected diode, exposing the module to the risk of overheating or even fire. A short circuit failure can occur due to high voltage when the diode has been either installed incorrectly or shortened. Besides these examples, bypass diode degradation can come out of high-temperature operating conditions, leading to semiconductor malfunctions [104; 105]. * **Encapsulants failure**. Encapsulants are elastomeric materials, usually made of EVA or alternative encapsulation materials such as thermoplastic polyolefins, ionomers, and polyolefin elastomers [106; 107]. The dominant degradation modes of encapsulants in a PV module are UV degradation, depletion of stabilizers, discoloration, and delamination. They also indirectly affect the degradation rate of the adjacent module components. _Discoloration_. Encapsulant discoloration is attributed to EVA degradation, which occurs due to the module's exposure to UV light. The presence of incompatible additives in the EVA leads to acetic acid formation, and the encapsulant is colored with a brown or yellow hue. The temperature factor also reinforces the phenomenon [44]. Modern encapsulant manufacturing techniques are based on lower additive concentration in EVA [65] or the utilization of additives with enhanced stability. _Delamination_. Encapsulant delamination is also a common failure mode that appears at the interfaces of the laminated layers. The term is used to describe detachment between different elements of the module and adhesion loss. Adhesion strength is affected by the aging of the encapsulant as well as all the chemical and physical procedures that take place [66; 67]. Delamination is proven to be hazardous for both the internal circuit and the solar cell, as it smooths the way for moisture or water inflow. Summarizing results are presented in Table 3. \begin{table}
\begin{tabular}{c c c c} \hline
**Degradation Cause** & **Description** & & **Effects on PV Modules** & **References** \\ \hline \multirow{4}{*}{Bubble formation} & Deterioration of ethylene-vinyl & \multirow{2}{*}{–} & Disrupts heat dissipation, leading to \\  & acetate (EVA) adhesion leads to & & overheating \\  & bubble formation due to thermal & & Increases reflectance of solar irradiance, \\  & decomposition and gaseous & & degrading performance \\ \hline \multirow{4}{*}{Corrosion and decreased adherence to contacts} & Caused by moisture permeation & \multirow{2}{*}{–} & Results in current leakage, diminished power \\  & through laminated edges, leading to & & output, and increased series resistance (Rs) \\ \cline{1-1}  & weak metallic connections & & Corrosion accelerates due to EVA degradation \\ \hline \multirow{4}{*}{Backsheet discoloration} & Backsheets are multilayered; & \multirow{2}{*}{–} & Yellow tint indicates reduced power output \\  & discoloration occurs from chemical & & over time \\ \cline{1-1}  & reactions producing chromophores & & Can lead to delamination and cracking due to \\ \cline{1-1}  & & polymer structure changes \\ \hline \end{tabular}
\end{table} 
Table 3: Key points regarding extrinsic degradation mechanisms affecting PV modules.