Influence of copper concentration in solutions on the growth mechanism and performance of electrodeposited Cu(In,Al)Se2 solar cells

• A change from instantaneous nucleation to progressive nucleation was observed by increasing copper concentration.
• The surface morphology and composition of Cu(In,Al)Se2 absorber layer change from cauliflower-like structure with Cu-poor composition to smooth, round structure with Cu-rich composition were influenced by the initial nucleation mechanism.
• The rough microstructure and undesired second phases cause recombination centers and induce leakage current, leading to diminish performances of solar cells.
• The highest conversion efficiency of our Cu(In,Al)Se2 solar cell fabricated at 2-mM copper concentration was 1.96%.

We conducted a chronoamperometric study to observe the electrochemical behaviors of the nucleation mechanism of electrodeposited Cu(In,Al)Se2 films. A change from instantaneous nucleation to progressive nucleation was observed by increasing the copper concentration. SEM and EDS analyses demonstrated that the surface morphologies and chemical compositions of precursor and post-annealed Cu(In,Al)Se2 films were influenced by the nucleation mechanism. They exhibited that Cu(In,Al)Se2 films had roughly cauliflower-like and triangular structures with Cu-poor composition at the instantaneous nucleation mechanism, whereas smooth and round structures with Cu-rich composition at the progressive nucleation mechanism. Additionally, the quality, growth orientation, composition phase, and optical energy band gap of Cu(In,Al)Se2 films were examined using X-ray diffraction (XRD) patterns, Raman spectra, and (αhν)2 vs. hν plots (UV–vis). Thereafter, the performances of rudimentary Cu(In,Al)Se2 solar cells fabricated at various copper concentrations were discussed, the conversion efficiency of electrodeposited Cu(In,Al)Se2 solar cells were unpublished in previous literatures. Our studies demonstrated that the performances of Cu(In,Al)Se2 solar cells were significantly related to the surface morphology and composition of Cu(In,Al)Se2 absorber layer. The highest conversion efficiency of Cu(In,Al)Se2 solar cells fabricated at a 2-mM copper concentration was 1.96% with open-circuit voltage, short-circuit current, fill factor, Rsh and Rs values of 0.189 V, 29.21 mA/cm2, 35.4%, 125 Ω and 2.82 Ω, respectively.