Effects of surface passivation at a SiO2/phosphorus-doped layer (n(+)-layer) front interface were investigated. Two kinds of cells with different surface concentration were fabricated. Surface potential at the interface was changed by applying bias voltage (V-F). Both open-circuit voltage and short-circuit current of the cell with n(+)-layer concentration of 3 x 10(18) cm(-3) depended on V-F. Internal quantum efficiency of this cell in short- and medium-wavelength range was changed by applying V-F. It was shown that cell performance was improved by the accumulation of electrons at the interface. To consider the work function difference between a material on the SiO2 film and the n(+)-layer is important, and cell performance can be further improved by applying V-F to passivate the SiO2/n(+)-layer interface.