Na effect on flexible Cu(In,Ga)Se2 photovoltaic cell depending on diffusion barriers (SiOx, i-ZnO) on stainless steel

• We fabricated CIGS-PV cells with diffusion barriers of SiOx and i-ZnO on STS.
• The efficiency of CIGS-PV cell with i-ZnO was ∼2% higher than that with SiOx.
• Distinctive defects were formed into CIGS absorber depending on diffusion barrier.

Cu(In,Ga)Se2 (CIGS) based-photovoltaic (PV) cells with different diffusion barriers of SiOx and i-ZnO were fabricated on stainless steel (STS) substrate and their electrical characteristics were investigated by measuring J–V curves under illuminated and dark conditions. The physical properties of the CIGS film depending on type of diffusion barrier were also analyzed using X-ray diffraction and secondary ion mass spectroscopy. The efficiency of the CIGS-PV cell with i-ZnO barrier was approximately 2% higher than that with the SiOx barrier. Through the analysis of dark J–V curves, we discovered that distinctive defects were formed in the band gap of CIGS based on which diffusion barrier contacted the STS. The diffraction pattern showed a slightly different tendency of the peak intensity ratio of (220/204)/(112) in the PV cell with the i-ZnO barrier, which was slightly higher than that in the PV cell with SiOx barrier. In elemental depth profile, a deficient Ga profile was observed near the surface of the CIGS film with the SiOx barrier, and an abundant Na profile within the CIGS film with the i-ZnO barrier was detected. This is attributed to a difference in thermal conduction through the diffusion barriers during CIGS film growth, originating from the larger thermal conductivity of ZnO compared with SiOx.

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