This prompted him to conduct experiments with photoconductivity. PVC was the first polymer whose photoconductivity was known. The underlying phenomenon is called sensitized photoconductivity. In 1873, Willoughby Smith discovered the photoconductivity of selenium. Willoughby Smith discovered the photoconductivity of the element selenium in 1873. Near zero carrier density graphene exhibits positive photoconductivity and negative photoconductivity at high carrier density. Whereas other Se forms are insulators, gray Se is a semiconductor showing appreciable photoconductivity. Some materials exhibit deterioration in photoconductivity upon exposure to illumination. His work followed the discovery of photoconductivity in selenium by Willoughby Smith in 1873. Combined with the photoeffect and photoconductivity, the electro-optic effect gives rise to the photorefractive effect. Sometimes avalanche photodiodes (APD), photoconductivity, photoelectromagnetic, or photodiffusion devices are used even without cooling. This higher conductivity in the presence of light is known as photoconductivity. Willoughby Smith, an English electrical engineer, discovered the photoconductivity of the element selenium in 1873. Polysilanes exhibit photoconductivity, although degrade when exposed to ultraviolet light. Photoconductivity allows the charged electrons to fall away from the areas exposed to light.