  Solution-processed amorphous silicon is a promising material for
semiconductor devices. Unfortunately, its manufacturing leaves a high density
of defects in the layer, which can be reduced by a treatment with hydrogen
radicals. Here, we present an optimized hydrogen treatment, which is used for
best performing solar cells made of solution-processed amorphous silicon. We
examine the amount and the nature of hydrogen incorporation using infrared
absorption and hydrogen effusion. The hydrogen treatment not only increases
hydrogen content significantly, it also enlarges the fraction of hydrogen in a
bonding configuration which is known to be advantageous for electronic
properties, albeit only close to the surface. Using electron spin resonance and
and photothermal deflection spectroscopy spectra, we confirm a reduction of
defect density. Regarding the electrical properties, the ratio of photo and
dark conductivity is increased by almost two decades. This leads to a greatly
enhanced performance of solar cell devices which use the material as the
absorber layer. In particular, the efficiency jumps by a factor of three.
