A recent publication in Energy & Environmental Science out of the Technical University of Denmark investigates the use of back-illuminated Silicon-based photocathodes for photoelectrochemical cells:
http://pubs.rsc.org/en/Content/ArticleLanding/2014/EE/C4EE03723E#!divAbstract
Many photoelectrochemical reactor/cell designs based on tandem (2 absorber) stacks employ Si as the bottom component, meaning that light will first pass through the back contact of this cell rather than the front surface where the electrochemical reaction is taking place.
Despite the practical necessity of back illumination in many PEC device designs, back illumination brings with it several challenges, including lower current density due to bulk recombination and complications associated with using a transparent conducting back contact.
Esposito Research Group Blog 