Improved performance of silicon heterojunction solar cells via 3× three-step boron-doping

To improve the doping efficiency of boron (B)-doped hydrogenated amorphous silicon [a-Si:H(p)] films, a three-step post-B-doping method was developed. This post-treatment method presents the potential to enhance not only the B content but also the hydrogen content in a-Si:H(p) films by increasing the number of treatment times. Based on secondary ion mass spectroscopy and dark conductivity measurements, the B concentration and efficiency of B-doping in a-Si:H(p) films were effectively improved by the three-step B-doping treatment. Furthermore, it was demonstrated that the atomic hydrogen generated during the B-doping process could diffuse into the a-Si:H(p) film and the underlying a-Si:H(i) layers, which is beneficial for suppressing the carrier recombination in the a-Si:H(p/i) passivation layers. There was an absolute increase of 600 μs in the effective minority carrier lifetime in the standard a-Si:H(n)/a-Si:H(i)/c-Si(n)/a-Si:H(i)/a-Si:H(p) structure by the 3× three-step treatment on the emitter side. Consequently, enhancements in both the open circuit voltage and the fill factor were observed, resulting in a 0.28% absolute gain (approximately) in the conversion efficiency of silicon heterojunction cells.