Effects of Annealing Pressure on Microstructure and Conversion Efficiency for Electrodeposited CuInSe₂ Absorbers

As-deposited CuInSe₂ thin films by electrodeposition method are usually accompanied with amorphous structure which is regarded detrimental for solar cell conversion efficiency. In this work, we proposed an annealing method under high pressure for improving the conversion efficiency of electrodeposited CuInSe₂ thin film solar cells, and the microstructure of high-pressure annealed CuInSe₂ films were also investigated. The annealing pressure was set from 100 kPa to 250 kPa, and the annealed CuInSe₂ thin films were then fabricated into solar cell using standard process. Field-emission scanning electron microscopy (FESEM) images show that CuInSe₂ films with higher annealing pressure demonstrate denser and smoother surface morphology. Results from X-ray diffraction (XRD) and Raman spectra indicate that annealing under high pressure enhanced the (1 1 2) preferential orientation of CuInSe₂ films and also eliminated binary Cu–Se phases. Finally, through annealing CuInSe₂ absorber layer under 200 kPa, the fill factor of the CuInSe₂ solar cell was found to be improved from 28.4% to 55% and the efficiency from 2.77% to 6.91%.