Researchers in Japan recently reported a triple-junction amorphous Si solar cell with a stabilized efficiency of 13.6%, a world record for triple junction thin film Si solar cells:
This triple junction solar cell is comprised of one a-Si cell, and two microcrystalline Si cells (uc-Si), whereas many triple junction a-Si cells demonstrated in the past have made use of amorphous silicon germanium (a:SiGe:H). A key reason these researchers were able to achieve the record stabilized efficiency is because the triple junction device was “current limited” by one of the uc-Si cells, which can exhibit very little initial performance degradation due to the Staebler-Wronski effect, which can significantly decrease the efficiency of amorphous Si solar cells.
The triple junction solar cell achieves a Vmpp of 1.58 V and Jmpp of 9 mA; a pretty good match for water splitting!
Here is an additional write-up from Phys.org: