Interdigitated back contact silicon solar cells featuring ion-implanted poly-Si/SiOx passivating contacts
Interdigitated back contact (IBC) silicon solar cells featuring passivating contacts based on tunneling oxides (SiOx) and n- and p-type polycrystalline silicon (poly-Si) thin films were fabricated with different rear side configurations to show the impact of the recombination in the transition region between p-type and n-type poly-Si on the performance of the solar cells. On the one hand a) p+ and n+ poly-Si regions were in direct contact to each other (""no gap"") using a local overcompensation (counterdoping) as a self-aligning process and on the other hand b) undoped (intrinsic) poly-Si remained between the p+ and n+ poly-Si regions (""gap""). These configurations were investigated in terms of recombination characteristics by illumination- and injection-dependent quasi-steady state photoluminescence (suns-PL) and were compared to solar cells that featured c) etched trenches separating the p+ and n+ poly-Si regions (""trench""). While the latter configuration allowed for open-circuit voltages (Voc) of 720 mV, fill factor (FF) of 79.6%, and short-circuit current (Jsc) of 41.3 mA/cm2, resulting in conversion efficiencies () of 23.7%, solar cells without a trench showed a poor performance due to non-ideal recombination in the space charge regions with high local ideality factors as well as recombination in shunted regions. Therefore, Voc of only 593 mV and FF of only 61.3% were achieved for the ""no gap"" configuration whereas for the ""gap"" configuration higher Voc of 680 mV but also low FF of 65.6% were obtained.