Earth-abundant Cu-based chalcogenide semiconductors as photovoltaic absorbers†
The materials Cu3PQ4 (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 μV K−1) indicating p-type behavior. Hole carrier concentrations are found in the range of 1016–1017 cm−3. Crystal structures of Cu3PS1.89Se2.11 and Cu3PS0.71Se3.29 are refined in the orthorhombic space group Pmn21 with the unit-cell parameters – Cu3PS1.89Se2.11: a = 7.5034(5) Å, b = 6.4951(5) Å, c = 6.2174(4) Å, and Cu3PS0.71Se3.29: a = 7.6164(6) Å, b = 6.5945(6) Å, c = 6.3107(5) Å. Photoelectrodes, fabricated from Cu3PSe4 single crystals, exhibit p-type photoresponse and yield open circuit voltages Voc = 0.12 V and short circuit currents Jsc = 0.25 mA cm−2 under 100 mW cm−2 of 660 nm illumination in a non-aqueous cobaltocene/cobaltocenium cell.