Underdense hydrogenated amorphous silicon (a-Si:H) prepared by plasma-enhanced chemical vapor deposition was used as a passivation layer in silicon heterojunction (SHJ) solar cells. By reducing the thickness of the underdense a-Si:H passivation layer from 15 nm to 5 nm, the open circuit voltage (Voc) of the corresponding SHJ solar cell increased significantly from 724.3 mV to 738.6 mV. For comparison, a widely used transition-zone a-Si:H passivation layer was also examined, but reducing its thickness from 15 nm to 5 nm resulted in a continuous Voc reduction, from 724.1 mV to 704.3 mV. The highest efficiency was achieved using a 5-nm-thick underdense a-Si:H passivation layer. We propose that this advantageous property of underdense a-Si:H reflects its microstructural characteristics. While the porosity of a-Si:H layer enables H penetration into the amorphous network and the a-Si:H/c-Si interface, a high degree of disorder inhibits the formation of the epitaxial layer at the a-Si:H/c-Si interface during post-doping layer deposition.

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To improve the passivation effect at a-Si:H/c-Si interface in heterojunction (HJ) solar cells, ultrathin SiOx layers with a thickness of approximately 2 nm were pre-formed on c-Si surfaces in chemical solutions. It was demonstrated that the SiOx layers pre-formed in hot de-ionized water and hydrochloric acid solutions improve effective carrier lifetime, and it is further enhanced through a post annealing process. When the thin SiOx layers were applied to HJ solar cells, increase in both Voc and Jsc was achieved, implying the improved interface quality for these HJ solar cells, as compared with the reference without the SiOx layer.

Hybrid heterojunction solar cells (HHSCs) using crystalline Si nanowires (SiNWs) as the absorber and conducting polymer poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) as the hole-selective transport layer (HTL) show great potential in both low-cost and high-power conversion efficiency (PCE). However, due to the poor wettability of the PEDOT:PSS solution on SiNWs, conformal coverage of PEDOT:PSS on SiNWs is not easy to achieve. Here, an effective method was developed to decrease the surface tension of the PEDOT:PSS and increase the wettability between PEDOT:PSS and SiNWs by incorporating organosilane into the PEDOT:PSS solution. Two kinds of organosilanes including tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMO) were selected as the additives. The surface passivation quality of the SiNWs was dramatically enhanced. The HHSCs utilizing VTMO as the additive show a higher open circuit voltage and higher PCE compared with the TMOS adding ones. By spin-coating Ag nanowires onto the PEDOT:PSS HTL layer and using spin-coated phenyl-C61-butyric acid methyl ester as the electron-selective transport layer, a champion PCE up to 18.12% and a fill factor of 80.1% have been achieved on the full solution processed PEDOT:PSS/n-type SiNWs HHSCs. The findings provide a simple and promising method to achieve high-performance PEDOT:PSS/SiNWs HHSCs.

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