Hi Luka,
Even for stellar spectroscopy you will probably find it easier to use a camera sensor (a 2D array) rather than a single channel photodiode. Although single channel photometers are occasionally still used in astro-photometry,
http://www.optecinc.com/astronomy/catalog/ssp/
It is pretty niche these days and CCD imaging sensors now prevail for astronomical photometry generally. Using an imager makes it much easier to see what is going on with focus, positioning etc and allows you to subtract the sky background without having to make a second set of measurements.
Cheers
Robin