To cite the service as such, we suggest the following BibTeX entry:
@MISC{vo:DOI_registration, year=2016, title={{VOiDOI} {DOI} registration web service}, author={Demleitner, M.}, url={http://dc.zah.uni-heidelberg.de/voidoi/q/ui/info}, howpublished={{VO} resource provided by the {GAVO} Data Center} }