The Photoelectrochemical Properties Of Solar Cells Based On Carbon Layer Modified TiO₂Thin Films

Dye-sensitized solar cells (DSSC) and quantum-dot sensitized solar cells (QDSSC) arephotoelectrochemial solar cells with similar configuration and photovoltaic mechanism. Theyhave attracted much attention due to their low cost, higher power conversion efficiency and easeof preparation. The photoanode based on semiconductor of wider band gap is the key componentof these solar cells. It is not only a substrate for sensitizer absorption but also a conductor ofphoto-generated electrons from the sensitizers to the anode. This project focuses on themodification of photoanode by introducing ultra-thin carbon layer as an interface between TiO2and sensitizer as well as an interface between sensitizer and electrolyte. The influence of carbonlayer on the light harvesting and electron transport in the TiO2photoanodes has been studied.Some interesting experimental results are summarized as below:1. Carbon-coated TiO2nanorod arrays (NRs) have been synthesized and used asphotoanodes in DSSC. The synthesis of carbon-coated TiO2NRs involves hydrothermal growthof oriented rutile TiO2NRs on transparent conductive glass and then coating a thin carbon layeron the surface of TiO2NRs in a subsequent hydrothermal process with glucose as carbon source.The DSSC based on carbon-coated TiO2NRs exhibited superior photovoltaic performancecompared to that based on normal TiO2NRs. It is suggested that the superior photovoltaicperformance was mainly ascribed to several advantages of carbon layer, which (1) suppressedthe recombination of photo-generated electron-hole pairs at the surface of TiO2NRs,(2)enhanced the electron collection in photoanodes, and (3) improved the harvest of light byenhancing the absorption of dyes on TiO2NRs. The optimal thickness of the carbon layer isabout6nm and the corresponding electrode photoelectric conversion efficiency is5.14%whichis higher than the efficiency1.03%of TiO2NRs. Excessive thickness of carbon layer hinders thelight absorption of dye and results in a negative effect on the power conversion efficiency ofDSSC.2. Carbon-coated TiO2NRs were used as photoanodes in QDSSC. The CdS quantum dotswere deposited on carbon-coated TiO2NRs by the successive ionic layer adsorption and reaction(SILAR) method. The results show that the power conversion efficiency of the QDSSC has beengreatly enhanced by carbon interfacial layer and the optimal thickness of carbon layer is6nm.The improved photovoltaic performance is ascribed to the reduced interfacial electronrecombination and enhanced electron collection in photoanodes.3. TiO2@C@CdS@C photoanode with double carbon layers, one layer on the surface of TiO2and the other layer on the surface of CdS, were fabricated based on TiO2nanoparticle film.The results showed that TiO2@C@CdS@C photoanode exhibits superior photoelectrochemicalperformance over TiO2@CdS, TiO2@CdS@C and TiO2@C@CdS photoanode. On one hand, thecarbon film can effectively suppress the photocorrosion of CdS quantum dots under lightirradiation. On the other hand, carbon layer can simultaneously reduce interfacial electronrecombination and enhanced electron collection in photoanodes.Therefore, thin carbon layer is proved to be a new interface modification material for thedevelopment of high efficient DSSC and QDSSC.