**Author details**

In fact, the studies described above do not reveal information about the full complexity of subsurface defect distribution effects. Therefore, there remains a wide number of uncertainties, e.g., the fundamental problem of whether or not the ultrasonic processing exploiting high acoustic powers is capable of promoting

To improve the photovoltaic response of Si wafers, SiGe and amorphous silicon (a-Si)/SiGe surfaces, a sonochemical treatment in hydrocarbon solutions of chloroform (CHCl3) and dichloromethane (CH2Cl2) can be employed. The use of the sonochemical reaction slows down the observed surface photovoltage decay and enhances its magnitude in SiGe and a-Si/SiGe thin layers grown on Si. The average surface-integrated photovoltage and decay time can increase up to 50%. This effect is not observed in distilled water, indicative of the fact that CH-containing radicals can lead to the observed improvements. It is suggested that the effect can be explained as follows. The hydrocarbon solution is decomposed and produces hydrocarbon chains, which are then decomposed further away into hydrogen and carbon. The reactive Si dangling bonds revealed on the surface of Si, a-Si or SiGe alloy layers are saturated by the hydrocarbon species to passivate the surface.

More work needs still to be done beyond the description of a very few links that have been highlighted above. In particular, the following experiments could pave the way for new mechanisms of surface passivation, activation of the interphase regions dangling bonds as well as cleaning of surfaces due to the ultrasonic

The work at Kyiv was funded by the Ministry of Education and Science of Ukraine (0119U100303). Financial support from the University of Vienna is also

effective cleaning without surface deterioration effects.

*Solar Cells - Theory, Materials and Recent Advances*

processing.

acknowledged.

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**Acknowledgements**

**Conflict of interest**

The authors declare no conflict of interest.

Andriy Nadtochiy<sup>1</sup> , Artem Podolian<sup>1</sup> , Oleg Korotchenkov<sup>1</sup> and Viktor Schlosser<sup>2</sup> \*

1 Faculty of Physics, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine

2 Department of Electronic Properties of Materials, Faculty of Physics, University of Vienna, Austria

\*Address all correspondence to: viktor.schlosser@univie.ac.at

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