**3.3 Study of the performance reduction mechanisms within the device**

Some micro-activities took place within the junction when the two materials (ZnS and CIGSe) are gathered together and are submitted to an external electric field and light. These activities which tend to reduce the global performances of the device, are the recombination mechanisms of the photo-generated electron-hole pairs. To recall what we said in **Section 1**, the first challenge of the current researches in the field of solar energy harvesting is the reduction of the quantities of materials while keeping the device performance or enhancing them. This is a great challenge since, the effects of the defect states, which inevitably appear with the reduction of thicknesses, have very detrimental effects on the performance of the cell.

#### *3.3.1 Charge carrier's recombination mechanisms*

These mechanisms are characterized by their rates R which describes the number of recombination per unit time and per unit volume of the material and by the lifetime of the charge carriers. There are three of them, but let us just consider the radiative and the Auger recombination.
