Improving the efficiency of quantum dot-sensitized solar cells by increasing the QD loading amount

In quantum dot-sensitized solar cells (QDSCs), optimized quantum dot (QD) loading mode and high QD loading amount are prerequisites for great device performance. Capping ligand-induced self-assembly (CLIS) mode represents the mainstream QD loading strategy in the fabrication of high-efficiency QDSCs. However, there remain limitations in CLIS that constrain further enhancement of QD loading levels. This review illustrates the development of various QD loading methods in QDSCs, with an emphasis on the outstanding merits and bottlenecks of CLIS. Subsequently, thermodynamic and kinetic factors dominating QD loading behaviors in CLIS are analyzed theoretically. Upon understanding driving forces, resistances, and energy effects in a QD assembly process, various novel strategies for improving the QD loading amount in CLIS are summarized, and the related functional mechanism is established. Finally, the article concludes and outlooks some remaining academic issues to be solved, so that higher QD loading amount and efficiencies of QDSCs can be anticipated in the future.

Near-infrared photoactive Ag-Zn-Ga-S-Se quantum dots for high-performance quantum dot-sensitized solar cells

The high light-harvesting ability of quantum dots (QDs) plays an eminent role in the performance of solar cells. In this study, we synthesized Ag-Zn-Ga-S-Se-based alloyed QDs by colloidal hot injection and characterized them. The X-ray photoelectron spectrum analysis confirms the +1, +2, +3, -2, and -2 oxidation states of, respectively, Ag, Zn, Ga, S, and Se in the QDs, and the energy-dispersive X-ray spectrum analysis confirms the 1:1:1:1.5:1.5 stoichiometric ratio of, respectively, Ag, Zn, Ga, S, and Se. These two results indicate the formation of I-II-III-VI₃-type alloyed crystals (AgZnGaS_1.5Se_1.5 nanocrystals). TEM image analysis reveals the QD nature of the synthesized Ag-Zn-Ga-S-Se nanocrystals. The X-ray diffraction pattern confirms the hexagonal structure. Due to the near-infrared light absorption capability, the synthesized QDs were used as the sensitizer to fabricate QDSCs. The fabricated QDSCs were characterized by using electrochemical impedance spectroscopy and photovoltaic performance studies. The fabricated QDSC have superior electrochemical activity with a photoconversion efficiency of 4.91%.

Preparation of SnIn4S8/TiO2 Nanotube Photoanode and Its Photocathodic Protection for Q235 Carbon Steel Under Visible Light

TiO₂ is an attractive semiconductor suitable for photocathodic protection, but its weak absorption of visible light and low quantum yield limit its usage. Here, a new heterostructured SnIn₄S₈ nanosheet/TiO₂ nanotube photoanode was prepared and its photocathodic protection performance was analyzed. SnIn₄S₈ nanosheets were uniformly deposited on the surface of the TiO₂ nanotube via a solvothermal treatment. The SnIn₄S₈/TiO₂ composite exhibited better photocathodic protection performance compared with pure TiO₂ nanotubes, owing to its good visible-light response and photogenerated carrier separation efficiency. Moreover, the composite exhibited a maximum photocurrent density of 100 μA cm^-2 for a 6 h solvothermal reaction under visible light irradiation. The negative shift of the photoinduced potential of Q235 carbon steel connected to the composite could reach 0.45 V versus SCE. Therefore, the SnIn₄S₈/TiO₂ composite can offer efficient photocathodic protection for Q235 carbon steel against corrosion in 3.5 wt% NaCl solution. This work provides a new approach for the development of high-efficient photoanode materials for the photocathodic protection of metals.

The hole transporting behaviour of Cu2AgInS4 and Cu2AgInSe4 for a carbon electrode-based perovskite solar cell

In this work, quaternary Cu₂AgInS₄ (CAIS) and Cu₂AgInSe₄ (CAISe) nanoparticles (NPs) were synthesised by a simple hot injection method and their photovoltaic behaviour were studied in detail for PSC.