POCL3-based co-diffusion process for N-type back-contact back-junction solar cells

Back-contact back-junction (BC-BJ) solar cells have been developed to meet the following objectives: process simplification by POCl3 based co-diffusion steps and efficiency improvement independent of the co-diffusion setup. In general, the process sequence is industrially feasible, requires not more than one temperature step (co-diffusion), and implements only industrially available patterning technologies. The process simplification is obtained by introducing a sophisticated co-diffusion process which combines solid diffusion sources with POCl3. Compared with BC-BJ cells featuring solid diffusion sources at the front side, the number of process steps could be decreased. Solar cells based on this process simplification feature conversion efficiencies up to 20.5 %. The efficiency improvement is obtained by integrating an improved B-source, by adjusting the material properties and by changing the pattern of the contact openings. BC-BJ cells based on the latter cell improvements feature conversion efficiencies up to 21.6 %. The efficiency improvement is transferable to cells based on the regarded process simplification featuring POCl3 as gaseous diffusion source.