When the photons with enough energy impinge on a photocathode, it emits electrons. Does this mean that the solid will lose all its electron at one point? If not, how are electrons restored?
When an electron gains enough energy from a photon of light, it can leave the surface of the metal - leaving the metal with a positive charge. But this positively charged piece of metal will attract an electron to become neutral again. Often, if 'left to itself' the photo electron will just fall back to the metal surface it came from.
If there is a positively charged electrode nearby, the electron will go there instead and a sensitive miliameter placed between the metal and the electrode will detect a small current as electrons will flow through the meter to make up the deficit.
There is a delicate balance of charge in nature.