ProjectProject Title : Improving the energy conversion efficiency of solar cell by spin caloritronics
Funding Agency : Department of Science and Technology (under SERC fast track Scheme)
Sanctioned Amount : Rs. 22.5 Lakhs
Duration of the Project : 3 Years [Completed Period Nov. 2013 to May 2017]
One of the main challenges of these coming years is to quickly find a means to drastically increase energy production to meet the growing energy demands of ever increasing global population. Major developed countries are investing heavily in developing new generation fuel cells, super capacitors, highly efficient inorganic and organic solar cells and fuel efficient vehicles. Fossil fuels which currently contribute to 63% of our energy production will run out eventually and in-foreseeable future the non-renewable energy is going to cost more and more as world crude oil resources and stocks in coal mines dwindles. The need for alternative energy sources in particular solar energy had been a focal point of major scientific research not only in India but around the globe.
The 26th Europeon Union Photovoltaic Solar Energy Conference held in Hamburg highlighted the importance of improving the performance of Solar cells for meeting the future energy demands. Even though there had been several new techniques proposed to overcome limting factors such as reflectance efficiency, quantum efficiency, charge carrier separation efficiency, and conductive efficiency, very little focus was given to thermodynamic efficiency which has a significant impact on energy conversion. For instance overheating caused by exposure to too much sunlight reduces power output of the solar panel and the problem is currently addressed by using water coolants. In addition to this, during the normal operation of a solar cell, any energy that is lost in a cell is converted into heat which again affects the power output. The thermodynamic aspect increases the cost of energy production in a conventional solar panel making it unviable for commercial applications.
In this research proposal a novel technique is proposed to improve the performance of solar cells by simultaneously cooling and scavenging the heat generated in the solar array. This is achieved by integrating the solar cell array with ferromagnetic nano-rods sandwiched between two non-magnetic materials and this nanorod assembly not only acts as heat sink but also generate useful energy from the dissipated heat by creating spin currents. The concept of generating spin current using temperature gradient across a ferromagnetic/non ferromagnetic junction is called “Spin Caloritronics” or “Spin seeback effect.
In a conventional non-ferromagnetic materials both spin up and spin down electrons carry the same amount of heat whereas in a ferromagnetic materials spin up and spin down electron carry different amount of heat as their chemical potentials are different. Therefore when ferromagnetic nanostructures are exposed to thermal gradients generates a spin polarized charge current – that is a current with more spin up electrons than spin down or vice versa will be induced.
The major advantages of the thermoelectric nano structures are the easy control of magnetic texture, highly localized power generation and refrigeration. It is also much simpler to integrate it with any micro and nanoscale electronic devices to function as heat sink and thermo power generators. If this spin seeback effect could be implemented as a heat sink for the solar cells, it will drastically improve the efficiency and additional power could be generated from the dissipated. The cooling efficiency of spin based materials will be far superior when compared to the conventional coolants currently employed in solar cells owing to the highly localized nature of the refrigeration. In this proposed project highly, localized thermopower generation and refrigeration will be created by using Au/Ni/Au nano-rod array which will be grown using electrochemical deposition with a porous anodized aluminum oxide membrane. This structure when fitted into the base of solar cell arrays will act as heat sink by drawing thermal energy from the circuits and converting them into spin voltage across the Au/Ni/Au nano-rod array. Temperature gradient across the Ni nano-rod array is created by the Au layers which will be in contact with the solar cell array by drawing thermal energy from the overlying solar panel.
SERB Project -2
Room temperature Hydrogen Storage and Sensing using graphene-MoS2 Nanocomposites
Funding Agency: Science and Engineering Research Project
Sanctioned Amount : 30 Lakhs
Duration of the Project : Completed (April 2017 -April 2020 )
Project Summary:
In this project, we propose to employ a composite of reduced graphene oxide (RGO) and Molybdenum di-sulphide (MoS2) for developing highly sensitive hydrogen detector and simultaneously utilize the highly porous structure of RGO for storing Hydrogen (H2). The structural integration of MoS2 Nanoparticle (NPs) in RGO matrix is expected to enhance the storage capacity and sensitivity to H2 by increasing the interlayer spacing and active sites in RGO. The addition of MoS2 NPs create more open ends resulting in more active sites, such as vacancies, defects and unsaturated bonds which greatly facilitate the adsorption and diffusion of H2. Also MoS2 NPs increases the H2 storage capacity by increasing the interlayer spacing by encasing between the rGO sheets. The successful implementation of the project will be a great step forward in making Hydrogen as an affordable fuel of choice.
RESEARCH GRANT 3: SERB: CORE RESEARCH GRANT
Experimental and theoretical investigations of ultra-thin two-dimensional semiconductor heterostructures and their application to make Nano-scale Devices
Funding Agency: Science and Engineering Research Board
Sanctioned Amount : 46 Lakhs
Duration of the Project : In progress (December 2020 - December 2023 )
Co-Principal Investigator : Dr. Swastibrata Bhattacharyya.
Project Objective (in brief):
All modern semiconductors based gadgets are moving fast from classical regime to quantum regime. The need for faster chips has logarithmically increased the transistor density and decreased the size of the devices over the past two decades. These changes bring have brought new challenges in developing technology to gain control over electron transport and reducing energy consumption. The problem associated with power consumption is now tackled by using power gating architecture which cuts the supply voltage to idle circuit domains. However quantum mechanics will take control over electron transport as the size of the devices continuously decreases. To develop this quantum based device technology, identifying new material systems and studying their intrinsic physical properties is a must. In parallel, systematic investigation needs to be carried out to develop CMOS like circuits with these new material systems which will deliver superior performance in terms of energy management and provide flexibility in transistor scaling.
In this research proposal we intend to study and develop electronic devices based on the heterojunction of Transition Metal Dichalcogenides (TMDCs) and graphene. Both graphene and 2D TMDC are the widely investigated layered material systems that have been isolated in monolayer form. Graphene was identified as one of the potential candidate for fabricating future transistor simply because of its ability to transport electron ballistically even at room temperature. However the absence of band gap has limited their application. Several attempts to engineer band gap in graphene have resulted in degrading the electron mobility of graphene. In contrast, compounds in the TMDC family have wide range of band gaps and they come in different forms such as metallic, half-metallic, and semiconducting. In particular, molybdenum and tungsten based TMDCs have band gaps ranging from the visible to the near-infrared spectral region. So for developing futuristic electronic devices, fabricating heterostructure which combines the complementary properties of TMDC and graphene would be the way forward.
The material systems we will be working on this project is the ultra-thin(< 50 nm) Graphene/MoS2 (WSe2) heterojunction, and MoS2/WSe2 heterojunction. Graphene, MoS2 and WSe2 as individual entities have different strength and weakness. Graphene, for instance, has higher mobility and low on-off ratio, whereas MoS2 and WSe2 have lower mobilities and higher on-off ratio. Hence we are focusing on making devices that work by manipulating the quasi-particle nature of electron in graphene and simultaneously exploiting the higher on-off ratio of TMDCs .
PROJECT SANCTIONED AS CO-PRINCIPAL INVESTIGATOR
Experimental and theoretical investigations of ultra-thin two-dimensional semiconductor heterostructures and their application to make Nano-scale Devices
Funding Agency: Nanomission
Sanctioned Amount : 2.14 Crores
Duration of the Project : In progress (December 2020 - December 2025 )
Principal Investigator : Prof. Santosh IIT Goa
Project Objective (in brief):
This proposed work will bring an understanding of quantum sciences in 2D materials from a quantum-technology perspective and will fabricate four nanophotonic devices to hosts single-photons, entangled-photon pairs emitters and to host single-spins. Two devices will have knobs to control the functionality of the devices. One will be able to control the tunneling of electron/hole and other will have an extra tuning knob of strain-tuning to control the optical properties of the emitters. For example, tuning of the emission color of the emitter is highly demanded so that emission from one emitter could be brought in resonance with other emitter to establish quantum gate, a similar counterpart of logic gates of conventional computer. Conventional hosts of quantum light emitters and host of single-spins are fabricated/grown either in diamond or in GaAs based materials and production cost of both materials are comparatively very high. For example, self-assembled GaAs or InAs based QDs are grown using a multi-million USD expensive machine, called Molecular-Beam-Epitaxy system, with a significantly high maintenance cost (approx. 100 lakh/year). As substrate-level atomically-thin sheet of 2D materials can be grown using an inexpensive CVD technique, and if similar qualities nanophotonic devices could be produced/fabricated using these 2D materials, and then it would be significant breakthrough for the future quantum technologies.