ZnS quantum dots (QDs) have limited application potential in QD sensitized solar cells because of their wide band gap, which does not allow absorption of sunlight in the visible and infrared regions. Introducing intermediate energy levels in the QDs is one way to expand the absorption window into the visible region. We show that this effect is achieved in Mn doped ZnS QDs. Mn doped ZnS QDs were synthesized by laser ablation in water and solution-based method. The structural, optical, and magnetic properties of the ZnS:Mn QDs have been examined by x-ray diffraction (XRD), transmission electron microscope (TEM), photoluminescence emission (PL) and excitation (PLE), and magnetic susceptibility measurements. The average particle size of cubic phase ZnS:Mn estimated from the XRD and TEM is about 3 nm. The QDs show two PL peaks near 450 nm and 600 nm, which are attributed to the defect related emission of ZnS and emission of Mn 2+ in a ZnS host, respectively. The PLE spectra exhibit near band edge absorption of ZnS at 350 nm and the absorption of Mn 2+ internal energy levels around 468 nm. The latter is due to the transitions of the 3d 5 electronic states of Mn 2+ from the ground state 6 A 1 to excited states 4 A 1 and 4 E and plays an important role in improving the absorption of the material in the visible region. ZnS:Mn QDs coated on Zn 2 SnO 4 nanowires show greatly improved sensitization in the visible region as demonstrated by incident photon to electron conversion efficiency experiments. Our study also shows that the characteristics of the solar cells performance can be tuned with the Mn concentration.

We report magnetoresistance (MR) manipulation and sign reversal induced by carrier concentration modulation in Mn-doped ZnO nanowires. At low temperatures positive magnetoresistance was initially observed. When the carrier concentration was increased through the application of a gate voltage, the magnetoresistance also increased and reached a maximum value. However, further increasing the carrier concentration caused the MR to decrease, and eventually an MR sign reversal from positive to negative was observed. An MR change from a maximum positive value of 25% to a minimum negative value of 7% was observed at 5 K and 50 KOe. The observed MR behavior was modeled by considering combined effects of quantum correction to carrier conductivity and bound magnetic polarons. This work could provide important insights into the mechanisms that govern magnetotransport in dilute magnetic oxides, and it also demonstrated an effective approach to manipulating magnetoresistance in these materials that have important spintronic applications.

In this work quantum dot sensitized solar cells (QDSSCs) were fabricated with CdSe and Mn-doped CdSe quantum dots (QDs) using the SILAR method. QDSSCs based on Mn-doped CdSe QDs exhibited improved incident photon-to-electron conversion efficiency. Carrier transport dynamics in the QDSSCs were studied using the intensity modulated photocurrent/photovoltage spectroscopy technique, from which transport and recombination time constants could be derived. Compared to CdSe QDSSCs, Mn-CdSe QDSSCs exhibited shorter transport time constant, longer recombination time constant, longer diffusion length, and higher charge collection efficiency. These observations suggested that Mn doping in CdSe QDs could benefit the performance of solar cells based on such nanostructures.

In this work, we report unusual observations of Kondo effect and coexistence of Kondo effect and ferromagnetism in Indium Tin Oxide (ITO) nanowires that were synthesized without incorporating any magnetic impurities. The temperature-dependent resistivity (ρ-T) data exhibited an upturn below 80 K and then tended to saturate below 10 K. The ρ-T and magnetoresistance data were analyzed using the n-channel Kondo model, and from the obtained values of S = 1 and n ~ 1, the nanowires were expected to be an under-screened Kondo system. A model was also proposed to explain the formation of localized S = 1 spin centers in the ITO nanowires. This work could provide insights into the understanding of spin-related novel phenomena in metal oxide nanostructures.

Zinc oxide nanowire and titanium dioxide nanoparticle (ZnO:TiO2 NW/NP) hybrid films were utilized as the photoanode layer in quantum dot-sensitized solar cells (QDSSCs). CdSe quantum dots (QDs) with a ZnS passivation layer were deposited on the ZnO:TiO2 NW/NP layer as a photosensitizer by successive ion layer adsorption and reaction (SILAR). Cells were fabricated using a solid-state polymer electrolyte and intensity-modulated photovoltage and photocurrent spectroscopy (IMVS/PS) was carried out to study the electron transport properties of the cell. Increasing the SILAR coating number enhanced the total charge collection efficiency of the cell. The electron transport time constant and diffusion length were found to decrease as more QD layers were added.