Semiconducting metal oxides are attractive for various applications since most oxides are non-toxic, stable, and easy to deposit. Wide band-gap materials have been studied more extensively, compared to low bandgap materials, which introduces limitations to the applications of oxides. Study of low band-gap semiconducting oxides can propel the usage of oxides in a wider range of applications. Here, the electronic, structural, and optical properties of Zn$_2$Mo$_3$O$_8$ (ZMO) are investigated. Stoichiometric polycrystalline films of ZMO are deposited using pulsed laser deposition system at room temperature. The unintentionally n-doped films show a hall electron mobility of 0.7 cm$^2$ V$^{-1}$ s$^{-1}$ and have a bandgap of 2.1 eV. The photoelectron spectra contain complex peak profiles which are explained to be a manifestation of final state effects. The orbital contribution to the valence band of ZMO is probed using resonant photoelectron spectroscopy, which confirms that the valence band is composed of Mo 4d levels. The conduction and valence band edges are predicted to be at 4.2 eV and 6.3 eV, so most of the conventional wide band-gap oxides can be used as hole-blocking layers with ZMO. Under A.M. 1.5 illumination, single-sided Schottky diode with Fluorine-doped tin oxide/TiO$_2$/ZMO/Au structure shows no photovoltaic action, possibly due to high exciton binding energy and low carrier drift lengths. However, the Schottky device shows a higher current under illumination, which suggests that with improvement in carrier drift lengths, ZMO can find applications in low-cost optoelectronic devices on flexible substrates like plastic or Polyethylene terephthalate.