Core-shell ZnO-CdX Nanocables Array Electrodes:Preparation And Photovoltaic Properties

Recently, semiconductor quantum dots (QDs) have been intensively utilized as sensitizers of wide-gap photoanodes including ZnO and TiO2in QDs sensitized solar cells (QDSSC). In these QDSSCs, the band alignment between the QDs and photoanodes always follow a type-Ⅱ mode, where both the valence and conduction bands of the QDs are higher in energy than those of the photoanodes. Specifically, sensitization with two kinds of narrow-gap semiconductors or one kind of narrow-gap alloy is an efficient way to increase the power efficiency of QDSSCs.Much effort has been paid on CdS/CdSe co-sensitized TiO2films solar cells because of the wide absorption range of CdSe and the suitable energy level of CdS in comparison with TiO2. Especially, energy level alignment at CdS/CdSe interface differs greatly from that at CdSe/CdS, which makes the TiO2/CdS/CdSe structure solar cell have better performance than the reversed structure of TiO2/CdSe/CdS. The co-sensitization of CdSe/CdTe on ID ZnO or TiO2photoanodes is less studied. Compared with CdS, CdSe and CdTe have wider absorption range due to the narrower band gap. Moreover, the conduction band edge of both CdSe and CdTe lies above that of ZnO, which makes it favorable in energy for the carrier injection from CdSe or CdTe to ZnO. Taking both the advantages of the co-sensitization method and nanocable arrays photoanode, double-sheath nanocable arrays based on CdSe and CdTe nanoshells and ZnO nanowire cores are expected as promising photoanodes of QDSSC.In this work, using ZnO nanowires cores as electrodes and CdSe and CdTe and CdSeTe alloy nanoshells as sensitizers, nanocable arrays are synthesized on ITO substrates by electrochemical deposition method. A contact interface is formed between the zinc-blende CdSe and CdTe of ZnO/CdTe/CdSe and ZnO/CdSe/CdTe nanocable arrays. In comparison with the poor photoelectrochemical property of the reversed structure, ZnO/CdSe/CdTe nanocables photoanode shows a saturated photocurrent as high as～14.3mA/cm2under the irradiation of AM1.5G simulated sunlight at45mW/cm2. As revealed by the detailed analysis on the interfacial energy alignment of CdSe/CdTe and CdTe/CdSe, a stepwise band alignment has been achieved among ZnO, CdSe and CdTe, which can greatly speed up the injection of the photoexcited electrons from CdTe and CdSe to ZnO.