Potential structure of c-Si bottom sub-cell in bifacial four-terminal III-V//c-Si multijunction devices

Abstract

We propose a structural innovation for a four-terminal III-V//crystalline silicon (c-Si) multijunction (MJ) device under bifacial illumination. The top cell is a double-junction gallium indium phosphide (GaInP)/gallium arsenide (GaAs) cell structure, and the bottom cell is a tunnel oxide passivating contact (TOPCon) structure with a boron-diffusion emitter and a wide-gap polysilicon oxide (poly-SiOx) passivating rear contact. To maximise the albedo-reflectance light transmitted into the c-Si absorber, the wide-gap poly-SiOx passivating contact is intended to replace the conventional narrow-gap polysilicon (poly-Si) passivating contact at the rear of the TOPCon. With an extra 0.25-sun illuminated light at the back, the bottom cell's conversion performance improves by 14.5%. When compared to mono-illumination, bifacial illumination increases the overall efficiency of the MJ device by 2.67%. The design shows great potential for enhancing further the conversion performance of the bifacial GaInP/GaAs//TOPCon MJ devices using the wide-gap poly-SiOx passivating rear contacts.