Improvement in Front-Contact Resistance and Interface Passivation of Heterojunction Amorphous/Crystalline Silicon Solar Cell by Hydrogen-Diluted Stacked Emitter

In heterojunction silicon solar cells (HJ-SCs), there is a possibility to reduce contact resistance at the front electrode by using a high-conductivity (σ_d) emitter. A hydrogen bonding configuration in the doped layers shows an increase in defect density with the doping, although the doping increases σ_d within a certain limit. Hence, a two-layer stacked emitter was used: one with a higher σ_d and the other with a reduced defect density. The emitter was stacked as a 3-nm-thick 3% doped (p2) layer with 7-nm-thick 0.5% doped (p1) double layer. A higher hydrogenation of the p2 layer showed better device performance, as it reduces series resistance from 2.4 to 1.5 Ω · cm². Furthermore, the carrier lifetime measurement, the atomic distribution across various layers, and the high-resolution transmission electron microscopy images show that the higher hydrogenation of the p2 layer might also have improved the a-Si:H/c-Si interface passivation, consequently improving the open-circuit voltage (V_oc) and efficiency (η) of the HJ-SCs. The experimental results were found to be consistent with simulation results. Finally, the HJ-SCs with the hydrogen diluted p2/p1 stacked emitter show V_oc of 710 mV, fill factor of 75.43%, and η close to 21%.