Microstructural changes in CdSe-coated ZnO nanowires evaluated by in situ annealing in transmission electron microscopy and x-ray diffraction

We report on the crystallite growth and phase change of electrodeposited CdSe coatings on ZnO nanowires during annealing. Both in situ transmission electron microscopy (TEM) and x-ray diffraction (XRD) reveal that the nanocrystal size increases from similar to 3 to similar to 10 nm upon annealing at 350 degrees C for 1 h and then to more than 30 nm during another 1 h at 400 degrees C, exhibiting two distinct growth regimes. Nanocrystal growth occurs together with a structural change from zinc blende to wurtzite. The structural transition begins at 350 degrees C, which results in the formation of stacking faults. Increased crystallite size, comparable to the coating thickness, can improve charge separation in extremely thin absorber solar cells. We demonstrate a nearly two-fold improvement in power conversion efficiency upon annealing.