Curcumin-Assisted Synthesis of MoS₂ Nanoparticles as an Electron Transport Material in Perovskite Solar Cells

Recently, two-dimensional (2D) transition metal dichalcogenides (2D TMDs), such as molybdenum sulfide (MoS₂) and molybdenum selenide (MoSe₂), have been presented as effective materials for extracting the generated holes from perovskite layers. Thus, the work function of MoS₂ can be tuned in a wide range from 3.5 to 4.8 eV by adjusting the number of layers, chemical composition, elemental doping, surface functionalization, and surface states, depending on the synthetic approach. In this proposed work, we attempt to synthesize MoS₂ nanoparticles (NPs) from bulk MoS₂ using two steps: (1) initial exfoliation of bulk MoS₂ into few-layer MoS₂ by using curcumin-cholesteryl-derived organogels (BCC-ED) and curcumin solution in ethylene diamine (C-ED) under sonication; (2) ultrasonication of the subsequently obtained few-layer MoS₂ at 60-80 °C, followed by washing of the above chemicals. The initial treatment with the BCC-ED/C-ED undergoes exfoliation of bulk MoS₂ resulted in few-layer MoS₂, as evidenced by the morphological analysis using SEM. Further thinning or reduction of the size of the few-layer MoS₂ by prolonged ultrasonication at 60-80 °C, followed by repeated washing with DMF, resulted in uniform nanoparticles (MoS₂ NPs) with a size of ~10 nm, as evidenced by morphological analysis. Since BCC-ED and C-ED produced similar results, C-ED was utilized for further production of NPs over BCC-ED owing to the ease of removal of curcumin from the MoS₂ NPs. Utilization of the above synthesized MoS₂ NPs as an ETL layer in the cell structure FTO/ETL/perovskite absorber/spiro-OMeTAD/Ag enhanced the efficiency significantly. The results showed that MoS₂ NPs as an ETL exhibited a power conversion efficiency (PEC) of 11.46%, a short-circuit current density of 18.65 mA/cm², an open-circuit voltage of 1.05 V, and a fill factor of 58.66%, at the relative humidity of 70 ± 10% (open-air conditions) than that of the ED-treated MoS₂ devices without curcumin. These results suggest that the synergistic effect of both curcumin and ED plays a critical role in obtaining high-quality MoS₂ NPs, beneficial for efficient charge transport, lowering the crystal defect density/trap sites and reducing the charge recombination rate, thus, significantly enhancing the efficiency.