  Accuracy of single-electron currents produced in hybrid turnstiles at high
operation frequencies is, among other errors, limited by electrons tunnelling
in the wrong direction. Increasing the barrier transparency between the island
and the leads, and the source-drain bias helps to suppress these events in a
larger frequency range, although they lead to some additional errors. We
experimentally demonstrate a driving scheme that suppresses tunnelling in the
wrong direction hence extending the range of frequencies for generating
accurate single-electron currents. The main feature of this approach is an
additional AC signal applied to the bias with twice the frequency as the one
applied to the gate electrode. This allows additional modulation of the island
chemical potential. By using the new approach under certain parameters, we
improve the single-electron current accuracy by one order of magnitude.
Finally, we show through experimentally-contrasted calculations that our method
can improve accuracy even in devices for which the usual gate driving gives
errors $\sim 10^{-3}$ at high frequencies and can bring them under $5\times
10^{-4}$.
