Abstract
Thin films of p-type Cu3BiS3 with an orthorhombic wittichenite structure, a semiconductor with high potential for thin film solar cell absorber layers, were synthesised by thermal annealing of Cu and Bi precursors, magnetron sputtered on Mo/glass substrate, with a layer of thermo-evaporated S. The elemental composition, structural and electronic properties are studied. The Raman spectrum shows four modes with the dominant peak at 292cm−1. Photoreflectance spectra demonstrate two band gaps EgX and EgY, associated with the X and Y valence sub-bands, and their evolution with temperature. Fitting the temperature dependencies of the band-gaps gives values of 1.24 and 1.53eV for EgX and EgY at 0K as well as the average phonon energy. Photoluminescence spectra at 5K reveal two bright and broad emission bands at 0.84 and 0.99eV, which quench with an activation energy of 40meV. The photocurrent excitation measurements demonstrate a photoresponse and suggest a direct allowed nature of the band gap.
Highlights
Large scale fabrication of thin film solar cells requires the development of photovoltaic (PV) technologies based on cheap and non-toxic elements abundant in the Earth's crust
At first 0.3 μm thick precursor layers of Cu and Bi were magnetron sputtered on Mo-coated soda-lime glass from 5 N-purity elemental targets. 1.5 μm thick films of 4 N-purity sulphur were thermally evaporated on these precursor layers
Such splitting has been reported for ternary I–III–IV2 semiconductor compounds with chalcopyrite structure [22,23]
Summary
Large scale fabrication of thin film solar cells requires the development of photovoltaic (PV) technologies based on cheap and non-toxic elements abundant in the Earth's crust. The basic electronic properties vital for development of Cu3BiS3 photovoltaic devices are almost unexplored, as reflected in the wide scatter of reported experimentally determined bandgap values from 1.14 [7] to 1.41 eV [8]. Theoretical studies of this compound suggested an indirect band gap of 1.69 eV while the smallest direct band gap was estimated to be of 1.79 eV [10]. Cu3BiS3 by thermal annealing of metal precursors with a layer of thermo-evaporated S and detailed characterisation of their structural, optical and electronic properties
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