Chemical tailoring of sodium content for optimization of interfacial band bending and alignment in flexible kesterite solar cells

In this study, highly efficient and flexible Na-doped kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells with an efficiency of over 8% were developed. A CZTSSe thin film was deposited on a Mo foil using metal precursors varying thickness the NaF layers film. The sample maintained 92.2% its performance after 1000 bending cycles radius 12 mm. To investigate defect passivation effect Na doping through electrical properties Na-passivated grain boundaries (GBs), examined by scanning probe microscopy. Downward band observed at GBs in Na-sufficient absorber layers; that is, enhanced potential barrier separation carriers. carrier increased under illuminated condition. Moreover, surface photovoltage (SPV) measured laser wavelengths 405, 532, 640 nm photo-assisted Kelvin force microscopy to photogenerated transport cells. content strongly affected photo-induced changes behavior. cell sufficiently layer exhibited large SPV maximum value 46 meV illumination, whereas Na-deficient samples showed lower SPV, indicating passivates defects act as recombination sites. optimal 405 wavelength condition, which resulted charge accumulation surface.