Plane waves are absolutely stable against small modulations in self-defocusing media, the dark spatial solitons exist only in the form localized dark hole on the plane wave background. Based on such modulation stability, the evolution equations for one-dimensional gray spatial solitons supported by the photovoltaic self-defocusing nonlinearity are presented and its stationary solution in photovoltaic photorefractive crystal LiNbO3∶Fe is given. The properties associated with these gray solitons are investigated numerically, such as soliton profile and its phase distribution for different values of soliton grayness, and the normalized transverse velocity and the normalized full width at half maximum (FWHM) of photovoltaic gray soliton as functions of normalized intensity and degree of grayness. These properties can be steered by adjusting the relative phase difference on either side of the soliton wave. Both similarities and differences between photovoltaic gray solitons and screening gray solitons are emphasized.