The difference between these two classifications is that photoconductive detectors use the increase in electrical conductivity resulting from increases in the number of free carriers generated when photons are absorbed (generation of current), whereas photovoltaic current is generated as a result of the absorption of photons of a voltage difference across a p-n junction (generation of voltage).
In general, photoconductive detectors have a higher frequency response, however they also have a higher signal to noise ratio. We recommend using photoconductive detectors if you are using a high-powered laser.