Electrophoretic Cu₂ZnSnS₄Thin Film For Counter Electrodes In Quantum Dot Solar Cell

Semiconductor quantum dot nanocrystals have unique optical and electrical properties due to the low dimensional effects such as quantum size effect, quantum confinement effect, impact ionization effect and miniband effect. So quantum dot solar cell is the great potential third generation solar cell. Counter electrodes in quantum dot sensitized solar cell play an important role in catalyzing reduction of the redox electrolyte by transferring electrons from the external circuit to the electrolyte. Platinum (Pt) is now regarded as a standard CE material in DSC system however, it is not efficient for application in QDSC based on polysulfide electrolyte. For the polysulfide electrolyte, however, strong interaction between Pt and sulfide ions is supposed to influence the conductivity and catalytic activity of Pt electrodes remarkably. However, cost and stability considerations necessitate developing compatible counter electrodes.Cu2ZnSnS4as a p-type semiconductor owing to its direct band gap of1.5eV, match the range of solar irradiation Cu2ZnSnS4is composed of naturally abundant elements in the Earth’s crust and has very low toxicity, it is environmentally friendly. So it is most widely known as one of the most promising photovoltaic.In this dissertation, Cu2ZnSnS4(CZTS) nanocrystal (NC) layers were deposited successfully by electrophoretic deposition (EPD) on fluorine doped tin oxide coated glass substrates. The summary are as follows:1. Work electrode:Cu2ZnSnS4nanocrystal layers were deposited successfully by electrophoretic deposition (EPD) on fluorine doped tin oxide coated glass substrates. And the layer thickness can be controlled by varying the concentration of NCs in dispersion, deposition time, and deposition voltage.2. Countereletrode:CdS were deposited by successive ionic layer adsorption and reaction (SILAR) on TiO2substrate.3. Assemble and test of the cells:Assembly of the cells and test and investigation of the phto-electric conversion properties of different types of working electrode Structures. The CdS QDSSCs with Cu2ZnSnS4electrode can present0.257of FF and0.683%of η, while the device with Pt electrode only presents0.140of FF and0.294%of η. Electrochemical impedance spectroscopy (EIS) has been applied to characterize the charge transfer resistance at electrolyte electrolyte/counter electrode interface. It is found that Rct of Cu2ZnSnS4-based CdS QDSSCs is much lower than that with Pt electrode, leading to higher FF, Jsc and remarkable improvement of the photovoltaic performance.