An experimental and computer simulation study of the role of CdS in CIS-type solar cells

An experimental and computer simulation study of the “red kink” current-voltage features seen in many CdS/Cu(In,Ga)Se₂ solar cells has been undertaken to gain more insight into cell operation and to address the controversy over the role of the CdS layer. The study shows that in structures with chemical bath deposited CdS: (1) the “red kink” effect is due to a low free electron concentration and high trap state concentration in the CdS layer, (2) the direct cause of the “red kink” is current modulated free electron concentration in the CdS, and (3) under white light the positive space charge built-up in CdS traps greatly enhances the photo-carrier collecting electric field in the absorber layer. Therefore, the CdS layer has an important role in the junction under white light