Instructive reviews are also provided by Shahbazi & Wang [153], where the metals penetration is particularly mentioned, and Wang et al. [154], that underlines the standardization of testing protocols. More recently, the mini-review by Qin et al. [155] comments on the latest improvements that present up to 3000 hours stable PCE. Figure  5 summarizes the above noted main elements involved in degradation and instability of PSCs. These factors mutually complement each either and the path for the devices stabilization is to avoid their conjunction, or individual excess.
 

IV.     HYSTERESIS OF PSCs

 
The current density-voltage (J V) characterization constitutes a fundamental tool for understanding the solar cells operation; and its performance under standard illumination conditions (air mass AM1.5, Pin = 100 mW·cm−2 [156]) is the established standard method for measuring the solar to electricity power conversion efficiency: