From single-layer optimization to tandem architectures: SILAR-grown PbS quantum dot thin films with enhanced conductivity

Abstract

Lead sulfide (PbS) quantum dot thin films with an average crystallite size of 1.2 nm were synthesized and systematically optimized for use as sensitizers in quantum dot-sensitized solar cells (QDSSCs), with an objective of achieving high film conductivity. The number of SILAR (Successive Ionic Layer Adsorption and Reaction) cycles was optimized at 10, while the complexing agent concentration in the cationic precursor was fixed at 2 drops per 60 ml, as higher concentrations were found to degrade conductivity. Incorporation of polyethylene glycol (PEG) as a conductive surfactant in this optimized single-layer film yielded a resistance of the order of 10⁻² Ω. To further enhance conductivity, tandem bilayer and trilayer PbS QD architectures were designed by combining layers of varying molar concentrations and SILAR cycles. The bilayer structure (centimolar bottom layer, millimolar upper layer) achieved a lower resistance of 10⁻³ Ω, a value that remained stable upon varying bottom-layer thickness. The trilayer structure (decimolar, centimolar, and millimolar layers) exhibited a resistance of 10⁻² Ω, irrespective of PEG incorporation. Overall, the optimized single-layer film requires 10 SILAR cycles, 2 drops of triethanolamine, and PEG surfactant, whereas optimized tandem structures (bilayer or trilayer) achieve superior conductivity without PEG, establishing viable, high-conductivity PbS QD architectures for QDSSC sensitizer applications. Further, the PbS quantum dot-sensitized solar cell device was optimized using SCAPS-1D simulation software, achieving a power conversion efficiency of 8.17%, which is in good agreement with reported literature values, thereby validating the experimentally optimized architectures for practical QDSSC applications.