Still, the photovoltaic see more properties of the resulting nanostructured solar cells are fairly poor [22, 24, 25, 27, 29, 32]. One explanation may be correlated to the thermal activation of CdTe NGs and NPs. For instance, it is well-known for p-CdTe/n-CdS heterojunctions that the use of CdCl2 heat treatment can significantly enhance the photovoltaic properties of the resulting solar cells . The CdCl2 heat treatment is expected to favor recrystallization of grains [34–37] as well as passivation of grain
boundaries (GBs) ; these are beneficial for the transport properties of the resulting solar cells . Nevertheless, very little is known concerning the effects of the CdCl2 heat treatment on the physical properties of ZnO/CdTe core-shell NW arrays. It is the aim of this paper to reveal the chemical and physical mechanisms following the CdCl2 heat treatment in ZnO/CdTe core-shell NW arrays as well as their effects on the photovoltaic performances. Methods Synthesis of ZnO/CdTe core-shell NW arrays on FTO thin films The synthesis of ZnO/CdTe core-shell NW arrays was achieved on fluorine-doped tin oxide (FTO) thin films by using low-cost chemical and physical deposition techniques. Polycrystalline FTO thin films were initially deposited by ultrasonic spray pyrolysis on a Corning C1737 borosilicate
Belinostat datasheet glass substrate (Delta Technologies, Ltd., CO, USA) heated at a growth temperature of 420°C. The chemical precursor click here solution was composed of 0.16 M of SnCl4 · 5H2O and 0.04 M of NH4F in a methanolic solution and sprayed at a constant flow rate of 1.25 mL/min for a given volume of 20 mL. The thickness of the FTO thin films is about 300 nm. The growth texture of the FTO thin films was controlled along the <100 > orientation in order
to favor the structural ordering of the layers grown on MYO10 top of them [40, 41]. The optical transmittance and electrical resistivity of the FTO thin films are about 90% and a few 10-4 Ω · cm, respectively. A seed layer of ZnO NPs was then grown at room temperature by dip coating. The chemical precursor solution consisted of zinc acetate dihydrate (ZnAc2·2H2O) and monoethanolamine dissolved in absolute ethanol in an equimolar ratio of 0.375 M. The withdrawal speed of 3.3 mm/s was used. All of the samples were initially pre-heated on a hot plate kept at 300°C for 10 min and subsequently post-heated on another plate at 540°C for 1 h. The thickness of the seed layer is about 20 nm. The growth texture of the seed layer was induced along the c-axis in order to favor the vertical alignment of ZnO NWs grown on top of them [42, 43]. Subsequently, the ZnO NWs were grown by CBD for 3 h in a chemical precursor solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and hexamethylenetetramine (C6H12N4) mixed in an equimolar ratio of 0.025 M, dissolved in de-ionized water, and heated at 90°C.