CdS QUANTUM DOTS SENSITIZED SINGLE-CRYSTALLINE TiO2 NANOWIRE ARRAY FILMS: PHOTOVOLTAIC PERFORMANCE AND PHOTOELECTRON TRANSPORT PROPERTIES

Single-crystalline rutile TiO2 nanowires were synthesized in situ on transparent conductive oxide (TCO) glass substrate and CdS quantum dots (QDs) were deposited on nanowires to form a TiO2/CdS heterojunction structure. The orientation growth, single-crystalline structure of TiO2 nanowire and the core-shell structure of TiO2/CdS were confirmed by XRD, SAED and HR-TEM measurements. The QD sensitized solar cells (QD-SSCs) were assembled and the optical, photoelectrical properties of QD-SSCs were investigated. The results showed that CdS QDs enhanced the optical absorbance of TiO2 in the visible region, therefore greatly improved the photovoltaic performance of solar cells. Under optimum parameters, a power conversion efficiency of 1.72% was achieved. Electron impedance spectroscopy measurement was also carried out to investigate the kinetics of charge transfer and recombination in QD-SSCs. The effects of amount of QDs and photoelectron transport properties of QD-SSCs on the cell efficiency were analyzed. It was proved that the amount of QDs was more important factor than electron lifetime and transfer rate for cell efficiency when the coverage of QDs on TiO2 was not high enough.