Perspectives for a-Si/c-Si heterojunction solar cells with p or n type base

In this paper, an overview is presented of amorphous silicon-crystalline silicon heterojunction solar cells on different base materials. We also tried to make a comparison with the classically used thermal diffusion. Cells were made with efficiencies of 15.8% and open circuit voltages up to 620 mV on p-type 1 Ωcm Fz material without the use of high efficiency features. When switching to 0.5 Ωcm p-type Fz material V_oc values increased up to 650 mV with a maximum efficiency of 16.4%. To be able to compare the p or n type base for the heterojunction approach, we also investigated the heterojunction emitter on n type Cz material with a thermally in-diffused phosphorus BSF. The highest efficiency achieved so far on this n-type material was 14.1% with a maximum V_oc of 630 mV. Despite the known shortcomings of p-type base hetero-junction solar cells compared to n-type base hetero-junction solar cells, they might find application in thin film solar cells. First result on thin freestanding films yielded efficiencies up to 9.6%. Using the heterojunction emitter instead of the diffused emitter higher V_oc were obtained on several investigated materials.