The circuit is normally completed at a scale where you can't use the electricity generated by the photo-electric effect.
To make is useable you have to somehow collect the electrons before they fall back to their base state. For that you need a semiconductor, which effectively creates a barrier across which the electrons can not travel back.
The little metal wires that are silk screened on to solar panels collect these free electrons and transport them to the edge of a photocell, where they can be used to drive a load on their way back to the substrate from which they've been liberated.
To make is useable you have to somehow collect the electrons before they fall back to their base state. For that you need a semiconductor, which effectively creates a barrier across which the electrons can not travel back.
The little metal wires that are silk screened on to solar panels collect these free electrons and transport them to the edge of a photocell, where they can be used to drive a load on their way back to the substrate from which they've been liberated.