Controlled bandgap CuIn_1−xGa_x(S_0.1Se_0.9)₂ (0.10 ≤ x ≤ 0.72) solar cells from electrodeposited precursors

Electrodeposition and post-annealing is a potentially low-cost industrial growth route for Cu(In,Ga)(S,Se)₂ solar cells. Nevertheless, this process is limited by the difficulty to introduce gallium in the precursor and by the segregation of gallium during the annealing step. Previously, we countered the former problem by co-electrodepositing In and Ga from a Deep Eutectic Solvent, accurately controlling the Ga/(Ga + In) (referred to as Ga/III) ratio of the precursor. In order to avoid segregation we employed a three-step annealing procedure, introducing a limited quantity of sulphur on the surface of the absorber. In this work, absorbers and solar cells originating from electrodeposited precursors with 0.10 ≤ Ga/III ≤ 0.72 are characterised. X-ray diffraction results show that the Cu(In,Ga)Se₂ 112 peak shifts to higher angles with increasing Ga content, in agreement with the expected composition values. Additionally, these results show identical incorporation of sulphur in all samples. Photoluminescence, external quantum efficiency, and current-voltage measurements corroborate the X-ray diffraction results. Controlled incorporation of Ga, over a large Ga/III range, is achieved for electrodeposited and post-annealed Cu(In,Ga)(S,Se)₂ absorbers. A maximum solar cell efficiency of 9.8% was obtained. - Highlights: • Electrodeposited Cu-In-Ga metal precursors with 0.10 ≤ Ga/(Ga + In) ≤ 0.72 were used. • The growth of Ga segregation free CuIn_1−xGa_x(S_0.1Se_0.9)₂ absorbers is reported. • A maximum solar cell efficiency of 9.8% was obtained