The wide bandgap, one-dimensional zinc oxide (ZnO) nanowires (NWs) and their heterostructures with other materials provide excellent pathways for efficient photovoltaic (PV) and light-emitting devices. ZnO NWs sensitized with quantum dots (QDs) provide high-surface area and tunable bandgap absorbers with a directional path for carriers in advanced PV devices, while ZnO heterojunctions with other p-type wide bandgap materials lead to light-emitting diodes (LEDs) with better emission and waveguiding properties compared with the homojunction counterparts. Synthesis of the structures with the desired morphology is a key to device applications. In this work, ZnO NW arrays were synthesized using hydrothermal method on ZnO and GaN thin films. Highly crystalline, upright, and ordered arrays of ZnO NWs in the 50 to 250-nm diameter range and 1 μm in length were obtained. The morphology and optical properties of the NWs were studied. Energy dispersive x-ray spectroscopy (EDX) analysis revealed nonstoichiometric oxygen content in the grown ZnO NWs. Photoluminescence (PL) studies depicted the presence of oxygen vacancy and interstitial zinc defects in the grown ZnO NWs, underlining the potential for LEDs. Further, hydrophobically ligated CdSe/ZnS QDs were successfully incorporated to the NW arrays. PL analysis indicated the injection of electrons from photoexcited QDs to the NWs, showing the potential for quantum dot-sensitized solar cells.
Knowledge of carrier transfer, in quantum dot sensitized solar cells, is the key to engineering the device structure and architecture optimization. In this work, Zinc oxide (ZnO) nanowire (NW) arrays were synthesized on glass wafers and on GaN thin films for application in photovoltaic and light-emitting devices. The nanowires grown on glass wafers were incorporated with CdSe/ZnS quantum dots (QD) and their steady state and lifetime photoluminescence (PL) were studied to investigate the feasibility of electron transfer from excited QDs to ZnO NWs. The results provide an indication that the injected electrons, from excited high quantum efficiency QDs, live longer and hence facilitate electron transport without undergoing non-radiative recombination at surface trap states. Morphology and optical properties of the ZnO nanowires on GaN film were also studied for application in light-emitting devices.
In this work preparation methods for spin-cast uniform layers of cadmium selenide (CdSe) quantum dots (QDs) with
specific thickness and subsequent film treatment methodologies are presented. Dimensional and lattice structures as well
as the homogeneity of the nanocrystals distribution over the film thickness are studied through high resolution
transmission electron microscopy (HRTEM). Ultra violet (UV) spectrometric and spectrofluorometric measurements are
performed to obtain absorption-emission spectrum of the provided films. The results show that the absorption is sensitive
to size of the nanocrystals and the refractive index of the medium in which they are embedded. Refractive index of the
thin films is extracted using spectroscopic Ellipsometery. Results are presented on the incorporation of the CdSe in glass
matrices and a graded index structure is optimized for embedment of nanocrystals. The photon conversion ability of the
fabricated layer has been verified. Effect of size and glass matrix contraction on the Raman shifts of CdSe quantum dots
has been also investigated. The results from such characterization methods are vital in knowing the properties of the
nanocrystals, as well as in optimizing a converter layer for solar cell applications.