Electro-optical Properties of Zn2Mo3O8 Thin-Films: A Novel Low-Bandgap Solar Absorber

Metal-oxide semiconductors are attractive as solar absorbers because they are abundant, stable, environmentally-safe, and low-cost. This work reports the electronic and optical properties of Zn
₂
Mo
₃
O
₈
(ZMO), a novel oxide-based solar absorber. ZMO has a direct bandgap of 1.9-2.1 eV, so it can efficiently absorb visible photons. As-deposited films are polycrystalline and unintentionally doped n-type with ~10
¹⁷
cm
^-3
carriers. Electron mobility of 0.6 - 0.7 cm
²
/V-s is comparable to other thin-film absorbers like CdTe. The conduction and valence band edges in ZMO are 4.4 eV and 6.3 eV below vacuum level, respectively. Preliminary devices show photoconductivity with a 1.5x increase in current upon illumination.