A new strategy of defect passivation in kesterite absorber layer to engineer the band tailing for efficient carrier transport

Abstract

Cu2ZnSnS4 (CZTS) absorber materials are often associated with high non-radiative recombination and band tailing which results in poor material properties. Herein, we successfully employ a small molecule, triethanolamine, to passivate the charged point defects and dangling bonds not only on the CZTS surface but also within the CZTS absorber. The Urbach energy of treated CZTS absorber reduced by 0.29 eV besides increased bandgap value unraveled the passivation of band-edge tail states. The band-to-band transitions (~ 6 times) enhanced over band-to-tail transitions in PL spectra after the treatment representing the significant suppression of non-radiative recombination. Our studies reveal that due to passivation of CZTS surface, the interface trap density was substantially reduced, influencing charge carrier dynamics of CZTS/TiO2 heterojunction-based devices. This work provides an insight toward the unexplored direction of chemical treatment of CZTS absorber to modulate its optical and electrical properties.