GeSe photovoltaics: doping, interfacial layer and devices.

Germanium selenide (GeSe) bulk crystals, thin films and solar cells are investigated with a focus on acceptor-doping with silver (Ag) and the use of an Sb 2 Se 3 interfacial layer. The Ag-doping of GeSe occurred by a stoichiometric melt growth technique that created Ag-doped GeSe bulk crystals. A combination of capacitance voltage measurements, synchrotron radiation photoemission spectroscopy and surface space-charge calculations indicates that Ag-doping increases the hole density from 5.2 × 10 15 cm -3 to 1.9 × 10 16 cm -3 . The melt-grown material is used as the source for thermally evaporated GeSe films within solar cells. The cell structure with the highest efficiency of 0.260% is FTO/CdS/Sb 2 Se 3 /undoped-GeSe/Au, compared with solar cells without the Sb 2 Se 3 interfacial layer or with the Ag-doped GeSe.