Earth-abundant Cu-based chalcogenide semiconductors as photovoltaic absorbers

The materials Cu(3)PQ(4) (Q = S, Se) of the enargite structure are studied as photovoltaic (PV) absorbers. Optical band gaps in the series Cu3PS4-xSex (0 <= x <= 4) are found to range from 2.36 eV (x = 0) to 1.35 eV (x = 4). Seebeck measurements on powder samples at room temperature yield large positive values (> 100 mu V K-1) indicating p-type behavior. Hole carrier concentrations are found in the range of 10(16)-10(17) cm(-3). Crystal structures of Cu3PS1.89Se2.11 and Cu3PS0.71Se3.29 are refined in the orthorhombic space group Pmn2(1) with the unit-cell parameters - Cu3PS1.89Se2.11: a = 7.5034(5) angstrom, b = 6.4951(5) angstrom, c = 6.2174(4) angstrom, and Cu3PS0.71Se3.29: a = 7.6164(6) angstrom, b = 6.5945(6) angstrom, c = 6.3107(5) angstrom. Photoelectrodes, fabricated from Cu3PSe4 single crystals, exhibit p-type photoresponse and yield open circuit voltages V-oc = 0.12 V and short circuit currents J(sc) = 0.25 mA cm(-2) under 100 mW cm(-2) of 660 nm illumination in a non-aqueous cobaltocene/cobaltocenium cell.