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This work shows that RF sputter-deposited hydrogenated amorphous silicon (a-Si:H) films are very effective in passivating silicon surfaces. We have previously found that sputter-deposited 45 nm thick intrinsic a-Si:H provides outstanding surface passivation on n-type silicon, similar to that achieved by 'classic' plasma enhanced chemical vapour deposition [1]. In this paper, we show that p-type silicon surfaces can be well passivated as well, achieving effective carrier lifetimes of 1.1 ms for a 1 Ω∙cm ptype wafer, compared to 4.5 ms for a 1.5 Ω∙cm n-type sample. Next, on n-type textured surfaces reasonable passivation is also achieved. Post-deposition annealing of our samples shows that sputtered a-Si:H films can perform similarly to PECVD deposited films in terms of thermal stability. Importantly, with stacks of intrinsic and doped (n or p) amorphous silicon effective carrier lifetimes of 1.9 ms and 1.6 ms on 1.5 Ω∙cm n-type wafers were obtained for i/n+ and i/p+ stacks respectively. These results underline the promise of sputter-deposited a-Si:H as an attractive alternative for heterojunction solar cell fabrication. However, dark conductivity measurements show that sputter-deposited doped a-Si:H films feature a relatively low conductivity, so far. We speculate that this may be caused by differences in microstructure compared to PECVD a-Si:H films, as suggested from the extracted optical band gap values for the respective films. ; This program has been supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). The authors from EPFL thank the Axpo Naturstrom Fonds, the European Commission (FP7 project Hercules), the EuroTech Universities Alliance and the Swiss Commission for Technology and Innovation for their financial support.

This work shows that RF sputter-deposited hydrogenated amorphous silicon (a-Si:H) films are very effective in passivating silicon surfaces. We have previously found that sputter-deposited 45 nm thick intrinsic a-Si:H provides outstanding surface passivation on n-type silicon, similar to that achieved by 'classic' plasma enhanced chemical vapour deposition [1]. In this paper, we show that p-type silicon surfaces can be well passivated as well, achieving effective carrier lifetimes of 1.1 ms for a 1 Ω∙cm ptype wafer, compared to 4.5 ms for a 1.5 Ω∙cm n-type sample. Next, on n-type textured surfaces reasonable passivation is also achieved. Post-deposition annealing of our samples shows that sputtered a-Si:H films can perform similarly to PECVD deposited films in terms of thermal stability. Importantly, with stacks of intrinsic and doped (n or p) amorphous silicon effective carrier lifetimes of 1.9 ms and 1.6 ms on 1.5 Ω∙cm n-type wafers were obtained for i/n+ and i/p+ stacks respectively. These results underline the promise of sputter-deposited a-Si:H as an attractive alternative for heterojunction solar cell fabrication. However, dark conductivity measurements show that sputter-deposited doped a-Si:H films feature a relatively low conductivity, so far. We speculate that this may be caused by differences in microstructure compared to PECVD a-Si:H films, as suggested from the extracted optical band gap values for the respective films. ; This program has been supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). The authors from EPFL thank the Axpo Naturstrom Fonds, the European Commission (FP7 project Hercules), the EuroTech Universities Alliance and the Swiss Commission for Technology and Innovation for their financial support.

Recurrent novae are repeating thermonuclear explosions in the outer layers of white dwarfs, due to the accretion of fresh material from a binary companion. The shock generated when ejected material slams into the companion star's wind can accelerate particles. We report very-high-energy (VHE; ≳100 giga–electron volts≳100 giga–electron volts) gamma rays from the recurrent nova RS Ophiuchi, up to 1 month after its 2021 outburst, observed using the High Energy Stereoscopic System (H.E.S.S.). The temporal profile of VHE emission is similar to that of lower-energy giga–electron volt emission, indicating a common origin, with a 2-day delay in peak flux. These observations constrain models of time-dependent particle energization, favoring a hadronic emission scenario over the leptonic alternative. Shocks in dense winds provide favorable environments for efficient acceleration of cosmic rays to very high energies.