Brownian motors binding energy diffusion transport quantum dots броуновские моторы броунівські мотори диффузионный транспорт енергія зв’язку квантові точки просторово розділені електрони і дірки Coulomb interaction broadening of bell-shaped distributions charge-transfer exciton coulomb and exchange interaction dichotomous process donor-acceptor systems molecular devices polarization effects potential barrier ratchet effect ratchet effect in Brownian photomotors spatially separated electron and holes spatially separated electrons and holes spherical interface splitting of electronic states stochastic fluctuation processes symmetry constraint symmetry of ratchet systems telegraph noise two germanium quantum dots