Light dependent current transport mechanisms in chalcogenide solar cells

Light dependent current transport mechanisms are the main reason for the failure of the superposition principle of dark and light IV curves of most chalcogenide solar cells. While the photocurrent collection is nearly constant, a significant variation of the forward bias characteristics of these devices takes place as effect of illumination. Different behaviours can be seen in different cells but the physical phenomenon underlying all these observations is the 'electronic doping' of the CdS window layer. A high density of deep trap centres with strongly asymmetrical Capture Cross-Section (CCS) changes radically the conductivity and type behaviour of this layer under illumination. The consequent bending and rearrangement of the energy bands modifies the current transport across the device. Different transport mechanism are analysed and modelled in the discussion.