The surface dipole and non-radiative recombination at p-Si(111) surfaces were investigated by in-situ photovoltage and photoluminescence techniques during the electrochemical formation of a Si \ organic layer interface by reduction of different diazonium salts. The reaction rate of the radical with the negatively charged p-Si(111) surface depends on the strength and the direction of the dipole moment of the radical. The formation of the surface dipole and of non-radiative surface defects, i.e. Si dangling bonds, correlates with the reaction rate. Well passivated Si \ organic layer interfaces can be prepared and the strong dependence of the surface band bending on the effective dipole moment of the grafted organic molecules has been demonstrated.