Research Activities
The TPG focuses on the basic understanding of thin-film growth and techniques by which their electro-optical properties can be tailored according to the target application. The acquired knowledge is then applied in energy-efficient devices such as organic light emitting diodes (OLEDs), transistors and photovoltaic cells to make them inexpensive, more stable and efficient.
The different research areas of interest are:
Development of Hybrid Transparent Electrodes
Solar cells, organic light emitting diodes (OLEDs), smartphone touch screens, liquid-crystal display (LCD), photo-detectors and many more optoelectronic devices have one thing in common, they all use a material which is transparent to visible light but at the same time can conduct electricity. Such components are commonly known as transparent electrodes (TEs) i.e., films that permit one to bring electrical currents or potentials in the proximity of optically active regions without significant loss of optical energy.
The current state-of-the-art optoelectronic devices are typically fabricated on substrates coated with ITO- indium tin oxide TE. ITO has been the subject of research and is refined for over 60 years and as a result, the material offers many beneficial properties that have made it the material of choice. However, it is widely believed that a shortage of indium (In) may occur in the near future because of the limited nature of world indium reserves. In addition, the next generation of optoelectronic devices requires TEs to be mechanically flexible. ITO being an oxide and thick (~150nm), is brittle and therefore cracks when bended. As such, the high-cost and scarcity of indium supply, together with its mechanical constraints has imposed an obstacle for the successful commercialization of the current optoelectronic technologies.
The group aims to develop indium-free TEs based on oxide-metal-oxide (OMD) architecture. Apart from that, TPG will also explore the possibility of using nanomaterials and their hybrid combinations for TE applications.
Optical modelling of Photovoltaic Devices
All optoelectronic devices can be seen as a stack of layers having different thicknesses with different optical constants i.e. refractive index and extinction coefficient. Transfer matrix method (TMM) which is basically solving the Fresnel's equations can be utilized to design any device stack to obtain optimal optical performance. The method allows not only to optimize the thicknesses of the different layers but also to introduce new layers which can boost the performance of the device.
Fundamental Growth Studies of Ultrathin Films
Ever since thin-film deposition techniques with sub-micrometer thickness control were developed, researchers have explored the question of how and when material properties (electrical, thermal, optical, magnetic, mechanical, chemical) of thin solid films deviate from the bulk properties of the deposited material. Such differences in observed parameters may arise, e.g., due to different size, shape and orientation of crystal grains, presence of interfaces, built-in stress, and/or due to morphological effects related to the particular mode of film growth. It is of great importance for numerous practical applications to fabricate ultrathin metal films (UTMFs) with a sub-nanometer scale roughness, low resistivity, and a high degree of thickness uniformity with properties similar to that of bulk metal. We are particularly interested in the growth mechanism of thin metal films and studying factors affecting their growth properties including use of nucleation/seed layers and self-assembled monolayers (SAMs)
Large Area Graphene Transfer
Graphene is a 2-D allotrope of carbon and is a material of interest, both for its fundamental understanding and applications. It is a single sheet of sp2 bonded carbon atoms having zero bandgap and thickness 3.4 Ă…. Ever since single-layer graphene burst onto the science scene, many studies were devoted to the production of isolated samples using the mechanical exfoliation of graphite. However, mechanical exfoliation can only yield relatively small samples with non-controllable sizes, therefore it cannot address the need for mass production of large-area and uniform monolayer graphene sheets. Recently, chemical vapor deposition (CVD) grown graphene on Cu has drawn considerable interest due to its potential for producing high-quality large-area graphene films. However, the difficulty in transferring CVD grown graphene films from Cu foil of large area to desired substrates without critical defects limits the physical performance of graphene and subsequently inhibits its commercialization.
We target to study and develop novel ways of transferring large area graphene sheet (at least 1cm x 1cm) onto desired substrates (e.g. glass, plastic and Si) with better coverage and quality for large area optoelectronic devices, including for transparent electrode applications. Use of sacrificial layers, transparent epoxy, polyimide and hydrophilic SAMs are some of the methods which would be explored and exploited to make large area transfer.
