Modulating Charge Carrier Dynamics through Selective Surface Deposition of a CdS Layer to Boost the Performance of AgBiS₂ Q-Dot-Sensitized Solar Cells

Despite having strong photoconductivity and a high absorption coefficient in Q-dot AgBiS 2, the efficiency of environmentally friendly light-harvesting AgBiS 2 -based solar cells remains low at 10.0%, far below the theoretically estimated 20% efficiency with a current density of 22 mA/cm 2 and V oc of 980 mV. The inherent short-carrier diffusion lengths and trap-assisted recombination properties of AgBiS 2 nanoparticles limit its thickness to ∼60 nm, beyond which a light parasite effect decreases performance. In this study, the charge carrier dynamics of the AgBiS 2 nanocrystalline film were modulated to minimize trap-assisted surface recombination and improve light harvesting by selective CdS layer coating in AgBiS 2 nanocrystals that resulted in an increase in J sc, V oc, and fill factor to 15.0 mA/cm 2, 0.352 V, and 47.0%, respectively, in contrast to AgBiS 2 without a CdS layer, which was 6.0 mA/cm 2, 0.248 V, and 37.0%. The electrochemical impedance data, IPCE measurements, and analysis of open-circuit voltage decay and intensity-dependent current/voltage parameters confirmed that the enhanced device performance was mostly due to a decrease in intrinsic trap-assisted recombination and the optical spacer effect. This study uniquely demonstrates the dual role of a selectively deposited CdS layer in AgBiS 2 nanocrystals, which inhibits trap-assisted recombination while also acting as a scattering layer.