Why The photovoltaic effect is the direct generation of electrical energy (a voltage and current) when light strikes a material, typically a semiconductor PN junction. Photons with enough energy free electron-hole pairs, and the junction's built-in field separates them, producing a potential across the terminals. This is the principle behind solar cells, which need no external bias to produce power.
Watch out The choice about emitting light when voltage is applied describes an LED, which is the reverse process (electroluminescence). The voltage-to-current conversion wording is just electrical, with no energy source created from the light.
Photo = light, voltaic = voltage: light in, voltage out. Solar cell, not LED.