Every material has optical and electrical properties. Light is always interacting with materials. The difference is that you're not applying a load. Or maybe you are and its just small...I'm not too familiar with biological materials. Either way, you need to complete the circuit and channel the electron flow.

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.