  Implementation of an optically active material on silicon has been a
persistent technological challenge. For tandem photovoltaics using a Si bottom
cell, as well as for other optoelectronic applications, there has been a
longstanding need for optically active, wide band gap materials that can be
integrated with Si. ZnSiP$_2$ is a stable, wide band gap (2.1 eV) material that
is lattice matched with silicon and comprised of inexpensive elements. As we
show in this paper, it is also a defect-tolerant material. Here, we report the
first ZnSiP$_2$ photovoltaic device. We show that ZnSiP$_2$ has excellent
photoresponse and high open circuit voltage of 1.3 V, as measured in a
photoelectrochemical configuration. The high voltage and low band gap-voltage
offset are on par with much more mature wide band gap III-V materials.
Photoluminescence data combined with theoretical defect calculations illuminate
the defect physics underlying this high voltage, showing that the intrinsic
defects in ZnSiP$_2$ are shallow and the minority carrier lifetime is 7 ns.
These favorable results encourage the development of ZnSiP$_2$ and related
materials as photovoltaic absorber materials.
