Earth-abundant Cu-based chalcogenide semiconductors as photovoltaic absorbers

The materials Cu sub(3)PQ sub(4) (Q = S, Se) of the enargite structure are studied as photovoltaic (PV) absorbers. Optical band gaps in the series Cu sub(3)PS sub(4-x)Se sub(x) (0 less than or equal to x less than or equal to 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 super(-1)) indicating p-type behavior. Hole carrier concentrations are found in the range of 10 super(16)-10 super(17) cm super(-3). Crystal structures of Cu sub(3)PS sub(1.89)Se sub(2.11) and Cu sub(3)PS sub(0.71)Se sub(3.29) are refined in the orthorhombic space group Pmn2 sub(1) with the unit-cell parameters - Cu sub(3)PS sub(1.89)Se sub(2.11): a= 7.5034(5) Aa, b= 6.4951(5) Aa, c= 6.2174(4) Aa, and Cu sub(3)PS sub(0.71)Se sub(3.29): a= 7.6164(6) Aa, b= 6.5945(6) Aa, c= 6.3107(5) Aa. Photoelectrodes, fabricated from Cu sub(3)PSe sub(4) single crystals, exhibit p-type photoresponse and yield open circuit voltages V sub(oc) = 0.12 V and short circuit currents J sub(sc) = 0.25 mA cm super(-2) under 100 mW cm super(-2) of 660 nm illumination in a non-aqueous cobaltocene/cobaltocenium cell.