Recombination Behavior of Photolithography free Back Junction Back Contact Solar Cells with Carrier selective Polysilicon on Oxide Junctions for Both Polarities
Abstract We report on ion implanted, inkjet patterned back junction back contact silicon solar cells with POLysilicon on Oxide (POLO) junctions for both polarities n+ doped BSF and p+ doped emitter. The recombination behavior is investigated at two different processing stages: before and after trench separation of p+ and n+ regions within polysilicon (poly Si) Before trench separation, we find a systematic dependence of the recombination behavior on the BSF index, i.e. the p+n+ junction meander length in the poly Si. Obviously, recombination at the p+n+ junction in the poly Si limits the implied open circuit voltage Voc,impl. at one sun illumination and the implied pseudo fill factor pFFimpl. to 695 mV and 80% respectively. After trench isolation, however, Voc,impl (pFFimpl. values increase up to 730 mV (85.5% corresponding to a pseudo efficiency of 26.2% for an assumed short circuit current density Jsc of 42 mA/cm2. We demonstrate a photolithography free back junction back contacted solar cell with p type and n type POLO junctions with an in house measured champion efficiency of 23.9% on a designated area of 3.97 cm2. This efficiency is mainly limited by the imperfect passivation in the undoped trench regions and at the undoped front side.