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

Abstract

In heterojunction silicon solar cells (HJ-SCs), there is a possibility to reduce contact resistance at the front electrode by using a high-conductivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\sigma _d}$</tex-math> </inline-formula> ) emitter. A hydrogen bonding configuration in the doped layers shows an increase in defect density with the doping, although the doping increases <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\sigma _d}$</tex-math> </inline-formula> within a certain limit. Hence, a two-layer stacked emitter was used: one with a higher <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\sigma _d}$</tex-math></inline-formula> 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⋅cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . 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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${V_{{\rm{oc}}}}$</tex-math> </inline-formula> ) and efficiency ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</i> ) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${V_{{\rm{oc}}}}$</tex-math></inline-formula> of 710 mV, fill factor of 75.43%, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</i> close to 21%.