what is difference between photodiode and solar cell in both light energy is used? light is packets of photons?

Hi,

A photo-diode is a semiconductor device consisting of a p-n junction made up of light sensitive material which is kept in reverse bias condition and when light falls on the junction, an electron is emitted because of inner photoelectric effect and a photo current is produced. This enables the diode to detect light. Thus, it is used as a light sensor.

On the other hand a solar-cell is an arrangement to produce electricity from sunlight based upon photoelectric effect.

Some properties of light like blackbody radiation/ PE effect etc are explained by considering the packets of energy (photon) consideration, while others like polarization, Diffraction, interference is explained by wave nature of light. At best structure of light can be said as a complementarity of wave and particle nature. No one can say what is light, the puzzle remains.