Efficiency Improvement by Charged-insulator Layers for IBC-SHJ Cells

A novel approach has been proposed to solve conversion efficiency degradation due to recombination loss at a gap region between p/i- and n/i-aSi:H layers in an interdigitated back contact Si heterojunction (IBC-SHJ) cell architecture. In our approach, a charged-insulator layer is newly introduced to cover the i-aSi:H on the gap region. Our simulation demonstrates that this leads to suppression of the recombination at the gap region, resulting in a significant improvement in the efficiency. Fixed-charge (Qf) with density of around 1012 cm-2 almost fully recovers the efficiency even with a low-quality surface at the gap around with the interfacial defect density of 1012 cm-2eV-1. The decrease in the recombination is owing to the field-effect passivation induced by the Qf. The recovery in the efficiency by Qf still works even though the quantum effects is considered, which causes some modification in the carrier distribution at the hetero-interface. Such charged-insulators are feasible by already existing materials such as Si nitride. In addition, this charged insulator architecture allows easy alignment for the backside structure. Thus, this proposal will be easily adopted for a mass production where the relaxed design rule is mandatory.