A hybrid tandem solar cell consisting of a thin-film, nanocrystalline silicon top junction and a siliconheterojunction bottom junction is proposed as a supporting solar cell for photoelectrochemical applications.Tunneling recombination junction engineering is shown to be an important consideration indesigning this type of solar cell. The best hybrid cell produced has a spectral utilization of 30.6 mA cm2a JSC of 14 mA cm2, a VOC of 1.1 V, a fill factor of 0.67 and thus an efficiency of 10.3%. A high solar-tohydrogenefficiency of 7.9% can be predicted when using the hybrid cell in conjunction with current a-SiCphotocathode technology.