Controlled growth of catalyst assisted and catalyst free CdSe micro cactuses with sharply pointed nanorods, their Photoluminescence (PL) and Photo electrochemical (PEC) properties

We report here a thermochemical approach for controlling the catalyst assisted and catalyst free growth of CdSe cactus like structures with sharply pointed nanorods (SPNR). The cactuses were simultaneously obtained on the silicon substrate and in semicircular alumina boat using cadmium and selenium powders as precursors under ammonia gas flow. The aqueous ammonia helps to control the growth of 1D structure and the formation of CdSe. Vapor-liquid-solid (VLS) growth mechanism is proposed for the catalyst assisted while solid state chemical reaction is suggested for the catalyst free growth of microcactuses. The microcactuses obtained in the boat as powder form are hollow whereas solid on the silicon substrate. Room temperature photoluminescence (PL) studies exhibit sharp peak at 672 nm for catalyst assisted CdSe microcactuses. A broad peak at 596 nm was observed for catalyst free growth of CdSe SPNR. In this work we have demonstrated that PL emission from the catalyst free growth of nanostructured CdSe is broad and intense. These two peaks are blue shifted from the bulk. Nanorods emerging from exterior surface of cactus like structures are observed to have decreasing diameter along vertical-axis and end up in SPNR. Average diameter in the middle of nanorods is estimated in the range of 250-450 nm. Photo electrochemical (PEC) solar cell is fabricated on ITO coated glass substrate with the help of PVDF in NMP solution. The efficiency and fill factor for as synthesized solar cell are 0.47% and 0.35 respectively. The as-prepared products were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM).