Flexible Cu(In,Ga)Se2 solar cell on stainless steel substrate deposited by multi-layer precursor method: its photovoltaic performance and deep-level defects

Cu(In,Ga)Se-2 (CIGS) films on soda-lime glass and stainless steel (SUS) substrates with several [Ga]/([Ga]+[In]), GGI, and Fe concentrations are fabricated by so-called multi-layer precursor method. From optical deep-level transient spectroscopy, deep-level defect located at 0.8eV from valence band maximum (E-V) is observed. This defect becomes recombination center when GGI is over 0.4, thereby decreasing cell performances. Fe-related deep-level defect is moreover detected in CIGS film on SUS substrate situated at 0.45eV from E-V. Its density is consistent with Fe concentration in CIGS films. According to SCAPS simulation and experimental results, Fe concentration of above threshold (1.0x10(16)atom/cm(3)) decreases carrier lifetime and carrier density and has more harmful influence on cell performances with GGI of above 0.4. On the other hand, Fe concentration of below threshold (1.0x10(16)atom/cm(3)) has no detrimental impact on cell performances. Namely, conversion efficiency () is slightly changed by below 2%. CIGS solar cell on SUS substrate with of 17.5% is fabricated by decreasing Fe concentration to approximately 5.2x10(16)atom/cm(3) although higher than the threshold value. Copyright (c) 2016 John Wiley & Sons, Ltd.