1. Definition and Principle

   - PID refers to the phenomenon of degradation of module performance in a PV module due to the presence of a potential difference between the cell and the bezel in a humid environment. When the potential difference inside the module is large enough, it causes ions in the encapsulation material to migrate, for example, sodium ions migrate from the glass surface to the n-type semiconductor side of the cell, which alters the electrical characteristics of the cell, such as lowering the fill factor, the open-circuit voltage, and the short-circuit current.

2. Influencing factors

   - Aspects of component structure

     - The encapsulation material and structure of the module have an impact on PID. For example, PID phenomenon is more likely to occur when an aluminum frame is used and the quality of the sealant is poor. This is because the electrochemical activity of the aluminum bezel is higher, and ion migration is easily triggered in the presence of a potential difference.

  External Environmental Factors

     - High humidity and high temperature environments exacerbate the PID phenomenon. High humidity provides the necessary medium conditions for ion migration, while high temperature accelerates the movement of ions. In general, the probability and severity of PID occurrence increases in environments with relative humidity higher than 85% and temperatures between 60 - 80°C.

   Electrical system aspects

     - The way the PV array is grounded and the way the PV modules are connected in series and parallel is also related to PID. If the grounding is poor or the positive and negative poles are not reasonably distributed when the modules are connected in series, it will lead to a large potential difference between the modules, thus triggering PID.

3. Prevention and solution measures

   -Component level*

     - Use PID-resistant materials, such as special encapsulating adhesive film. Some high-performance encapsulating adhesive films have low ionic conductivity and can effectively prevent ionic migration.

     - Optimize the electric field distribution between the cell and the frame during the module design and manufacturing process to reduce the generation of potential difference.

   System level

     - Reasonable grounding design for PV arrays, such as the use of negative grounding can reduce the potential on the surface of the module, reducing the possibility of PID occurrence.

     - Install PID repair devices that can apply reverse potential to the module at night or when the light is weak, driving migrating ions back to their original positions and thus restoring the performance of the module.

II. LID (Light - Induced Degradation)

1. Definition and Principle

   - LID refers to the phenomenon of gradual decline in the performance of PV modules under long-term light exposure. For crystalline silicon PV modules, it is mainly due to the formation of boron-oxygen complexes in silicon wafers under light exposure, resulting in an increase in the minority carrier complex. In p-type crystalline silicon, boron is a common doping element that forms boron-oxygen complexes when oxygen is present. These complexes act like traps, trapping the minority carriers and making the lifetime of the minority carriers lower, which in turn reduces the photoelectric conversion efficiency of the cell.

2. Factors affecting

   -Silicon wafer quality

     - The impurity content and crystal defects in the silicon wafer affect the degree of LID. If the boron content in the wafer is too high or there are more crystal defects such as dislocations, it will accelerate the occurrence of LID.

   - Light intensity and duration

     - Higher light intensity and longer light duration will make the LID phenomenon more obvious. Generally speaking, under standard test conditions (STC), the power of the module will gradually decrease with the accumulation of light exposure time.

3. Prevention and solution measures

   - Silicon wafer manufacturing process

     - Optimize the purification process of silicon wafers to reduce boron content and crystal defects. For example, adopting more advanced crystal growth technology, such as the modified Siemens method, can improve the purity of silicon wafers.

   - Module manufacturing and system operation

     - In the process of module manufacturing, some pretreatment technologies can be used, such as light annealing treatment. By pre-irradiating the components under certain light intensity and time conditions, the formation of the boron-oxygen complex can be triggered in advance, so that it reaches a relatively stable state at the beginning of the normal use of the components and reduces the subsequent LID loss.

     - In system operation, the heat dissipation system of the component is reasonably designed, because high temperature also exacerbates the LID phenomenon. Good heat dissipation can make the components maintain better performance in high temperature environment.