Effect of different halide-based ligands on the passivation and charge carrier dynamics in AgBiS2 nanocrystal solar cells

Abstract

AgBiS₂ nanocrystals have been shown to be a promising material for solar cell applications due to their high absorption coefficient, solution-processability and stability. However, detailed and systematic insight into how different surface passivation agents affect the overall material properties and corresponding device performance is still limited. Herein, a study about AgBiS₂ nanocrystals treated with five different halide-based compounds – TBAI, TMAI, TBABr, TMABr and TMACl – is presented, with the nanocrystals themselves being synthesised via a newly adapted route under atmospheric conditions. For the differently passivated samples, variation in the ligand uptake, as well as shifts in the position of the valence and conduction bands could be observed. Incorporating these ligand-treated thin films into solar cell devices allowed for further investigation of their overall performance as well as into their respective charge carrier dynamics. Markedly longer charge carrier lifetimes were observed for the bromide- and chloride-passivated samples through transient photovoltage and photocurrent measurements as well as impedance spectroscopy. The effect of the surface modification on the charge carrier transport behaviour, on the other hand, was found to be less pronounced. Overall, this work demonstrates the importance of better understanding how different ligands affect nanocrystal properties, showcasing how it influences a wide variety of parameters controlling final device performance.