Yatin J. Mange

NiO Nanofibers as a Candidate for a Nanophotocathode

p-type NiO nanofibers have been synthesized from a simple electrospinning and sintering procedure. For the first time, p-type nanofibers have been electrospun onto a conductive fluorine doped tin oxide (FTO) surface. The properties of the NiO nanofibers have been directly compared to that of bulk NiO nanopowder. We have observed a p-type photocurrent for a NiO photocathode fabricated on an FTO substrate.

In-situ local temperature measurement during three-dimensional direct laser writing

We present an approach to measure in situ the local temperature increase in the exposed volume during three-dimensional direct laser writing. The method is based on the detection of luminescence from NaYF4:Yb3+, Er3+ co-doped nanocrystals in a confocal scheme. We found the temperature increase to be below a few K within the normal writing regime. If the photoresist is overexposed, significant temperature changes of several hundred K can be observed.

CuInS2/ZnS nanocrystals as sensitisers for NiO photocathodes

Nickel oxide (NiO) is the most universally studied photocathode to date, however, its poor fill factor (FF) makes its efficiency much lower than its counterpart, n-type photoanodes. Its significance in photovoltaics is based on the potential to fabricate tandem photoelectrodes in order to enhance the overall efficiency of the existing devices. Furthermore, limited work on the sensitisation of NiO with semiconducting nanocrystals (NCs) exists. For the first time, we have fabricated NiO photocathodes sensitised with aqueous CuInS2/ZnS NCs. The NCs were chemically bound to the NiO films with the aid of carboxyl and thiol groups. This was achieved without modifying the bulk surface properties of NiO. Binding of the NCs was investigated using TEM, SEM, XPS, XANES, EXAFS modelling and ToF-SIMS. NiO films were assembled into CuInS2/ZnS NC sensitised photocathodes and their photovoltaic properties were compared to those of unsensitised and dye-sensitised NiO solar cells. We demonstrate that non-toxic NCs can be used to sensitise NiO photocathodes to achieve an (almost) all-inorganic system.

Three-dimensional micro-printing of temperature sensors based on up-conversion luminescence

The pronounced temperature dependence of up-conversion luminescence from nanoparticles doped with rare-earth elements enables local temperature measurements. By mixing these nanoparticles into a commercially available photoresist containing the low-fluorescence photo-initiator Irgacure 369, and by using three-dimensional direct laser writing, we show that micrometer sized local temperature sensors can be positioned lithographically as desired. Positioning is possible in pre-structured environments, e.g., within buried microfluidic channels or on optical or electronic chips. We use the latter as an example and demonstrate the measurement for both free space and waveguide-coupled excitation and detection. For the free space setting, we achieve a temperature standard deviation of 0.5 K at a time resolution of 1 s.

A quantum dot sensitized catalytic porous silicon photocathode

Solar fuels have attracted considerable attention as an alternative energy vector in the context of the dwindling supplies of the planets non-renewable resources. The first step in solar fuel generation is often a photo-catalytic water splitting. Although a very large amount of work has been dedicated to optimise the photo-oxidation process (mostly based on titania), the development of highly efficient photocathodes is limited. In this paper, we report the fabrication and characterisation of a nano-structured photocathode using indium phosphide QDs and a bio-inspired Fe2S2(CO)6 catalyst, p-type porous silicon photocathode. Our hybrid electrode system produced a photocurrent density of −1.2 mA cm−2 with hydrogen evolution at low bias potentials.

Cation exchange of aqueous CuInS2 quantum dots

Chalcopyrite copper indium disulfide (CIS) QDs have been of recent interest due to their non-toxicity. Although publications on CIS QDs are becoming more common, the majority of synthesis involves long chained insulating ligands, which are only soluble in non-polar solvents. Recent works have explored the tunable properties of CIS QDs by means of cation exchange with ZnS. Despite this, their tunable properties have been limited to use in organic solvents. This may be due to the cation exchange not being completely understood. For the first time, we present a controllable cation exchange for water soluble, tunable CIS QDs. We also show the partial exchange of indium for zinc, which is shown to provide these QDs with unique optical properties.

Rapid microwave assisted synthesis of nearly monodisperse aqueous CuInS2/ZnS nanocrystals

A rapid microwave-assisted synthesis for nearly monodisperse CuInS2/ZnS nanocrystals (NCs) has been developed. CuInS2/ZnS NCs have been prepared in water using thioglycolic acid as a stabilising ligand. The proposed synthesis results in stable and monodisperse NCs after only 5 minutes. In addition, the NCs were tested as potential sensitisers for photoanodes.

{Ni4O4} Cluster Complex to Enhance the Reductive Photocurrent Response on Silicon Nanowire Photocathodes

Metal organic {Ni4O4} clusters, known oxidation catalysts, have been shown to provide a valuable route in increasing the photocurrent response on silicon nanowire (SiNW) photocathodes. {Ni4O4} clusters have been paired with SiNWs to form a new photocathode composite for water splitting. Under AM1.5 conditions, the combination of {Ni4O4} clusters with SiNWs gave a current density of −16 mA/cm2, which corresponds to an increase in current density of 60% when compared to bare SiNWs. The composite electrode was fully characterised and shown to be an efficient and stable photocathode for water splitting.

3D Micro-printing of Optical Temperature Probes

We present printable optical temperature probes to monitor the temperature with a spatial precision on the micrometer scale. Our approach is based on the temperature-dependent upconversion fluorescence from NaYF4:Yb3+, Er3+ co-doped nanocrystals. These nanoparticles are dispersed in a standard photoresist for direct laser writing, allowing for spatially resolved micro-printing of single or multiple probe spots. For demonstration, we decapsulate a fully operational integrated circuit and print temperature probes directly on the semiconductor chip to monitor its local heating. The printability of the probes facilitates an easy integration into diverse systems, especially when aiming at integrated optics or lab-on-a-chip systems.