Doping Variation at the TCO/a-Si(p) Hole Contact
Resistive losses arise at the transport barriers at the interfaces between the different semiconductor materials in the TCO/a-Si/c-Si stack and limit the power output of silicon heterojunction (SHJ) solar cells. A key element is the unisotype recombination junction at the TCO/a-Si(p) interface. We identify sufficient doping on both sides of this junction to be crucial for low contact resistance ( c). For a-Si this is achieved by using a sufficient but not too high doping gas concentration during deposition. On the TCO side high oxygen (O2) gas concentrations during deposition have to be avoided. To combine high transparency of O2-rich TCOs with low c and Rsheet of O2-poor TCOs, we utilize a TCO layer stack. We show that a low O2 content in the vicinity of the TCO/a-Si(p) interface is mandatory to provide efficient tunnelling transport and to avoid resistive losses at the TCO/a-Si(p) interface.