Electrophotographic photoreceptor and image formation apparatus

An image forming apparatus comprising:

• An organic photoreceptor comprising a charge generation layer and a charge transport layer provided on a conductive substrate, wherein
• the substrate has a ten-point surface roughness Rz of the substrate of 0.2 μm or less.
• the charge generation layer comprises particles of a condensed polycyclic pigment, having an average major axis length of 500 nm or less, an average aspect ratio of 2.5 to 5.0, and an aspect ratio variation coefficient of 16% or less, and
• quantum efficiency Φ of the photoreceptor is not less than 0.5. the quantum efficiency Φ being defined by a Formula of Φ=ΔQ/(n0×e), wherein ΔQ is reduced amount of charge [C] in case that light having light amount predetermined so as to make the electric field E becomes ⅔ times of initial electric field after unit time (1 sec.) is exposed to the organic photoreceptor under condition of the initial electric field E0=2.5×105 [V·cm−1], and no is a number of incident photons per unit area (1 cm2) and in unit time (1 sec.) in terms of [cm−2·s−1] in case that light having light amount predetermined so as to make the electric field E becomes ⅔ times of initial electric field after unit time (1 sec.) is exposed to the organic photoreceptor under condition of the initial electric field E0=2.5×105
• [V·cm−1], and e is an elementary electric charge 1.3×10−19 [C].
• a charging device to charge the organic photoreceptor;
• an exposure device to form an electrostatic latent image by exposing the organic photoreceptor charged with the charging device to light;
• a developing device to form a toner image via development of the electrostatic latent image with a toner;
• and
• a transfer device to transfer the toner image from the organic photoreceptor to a transfer medium,
• wherein the exposure device comprises an exposure light source of monochromatic light having a wavelength of 350-500 nm.