Nanoimprint Lithography for Crystalline Silicon Solar Cells

A.Mahaboobbatcha, O. K. Simya, M. Sureshmohan & K. Balachander

Nanoimprint Lithography (NIL) is a state-of-the-art imprinting technique for

patterning in nano-scale regime down to 10nm. This technique has proven track record

in semiconductor industries. Hence, it has been added to the International Technology

Roadmap for Semiconductor (ITRS) for 32 and 22 nm nodes. The screen printing is

available worldwide technology for front-side metallization of silicon solar cells;

however it has limitations related to the quality of printing below a certain limit. To

overcome this issue, the advanced metallization technique using Nanoimprint

lithography is being explored. In order to achieve the high efficiency and low cost

crystalline silicon solar cell, the integration of Nanoimprint lithography technique is most

beneficial to achieve high throughput and high quality imprinting. The Nanoimprint

lithography have superior qualities like less silver usage, leading to higher efficiencies,

high printing accuracies, low operation and installation cost and high throughput.

Proposed design for Nanoimprint lithography tool

THIN FILM SOLAR CELLS

O. K. Simya, Mahaboobbatcha, M. Sureshmohan & K. Balachander

Thin film solar cells are made by depositing one or more thin layer of PV material on a

substrate. It is developed as a response to high material usage and cost of crystalline silicon

solar cells. Our main focus is the fabrication and characterization of nano-structured CZTSSe

based thin film solar cells. For this to initiate, the primary aim is to fabricate a high quality

crystalline CZTS, CZTSe and CZTSSe absorber layer using a hybrid PVD tool. In order to get a

high quality layer, the deposition temperature, sputter targets, sputter power, working

pressure and the individual elemental fluxes are the most important parameters that would

be potentially explored during the deposition process.We are now in the pathway of

developing novel nanosturctured thin film solar cells using a nanoimprint lithography

technique. The formation of nanopillar array creates a periodic patterning of PN junction,

which facilitates increased power conversion efficiency, owing to increased junction area,

smaller distance between carrier generation and collection, extreme light trapping, reduced

reflection, improved bandgap tuning, increased defect tolerance and the resonance effect.

Simulation has become an essential tool for the detailed understanding, inputs to

experimental optimization and further evaluation to study optical and electrical behaviour

Novel Nanostructured

Thin film Solar Cells

Conventional Thin film

Solar Cells

of the materials involved. We are working with the SCAPS simulation program in order to

facilitate complete understanding about the performance of CZTS, CZTSe and CZTSSe based

thin film solar cell, and also to fabricate cells with champion efficiencies, a detailed analysis

of all the layers involved in solar cell have to be evaluated

Design of thin film in SCAPS environment

Organic Solar Cells

M. Sureshmohan, O. K. Simya, A. Mahaboobbatch & K. Balachander

The demand for energy is increasing day by day and a source to fill the demand has

initiated the research and optimization on organic solar cells for their low cost consideration

in contrast with silicon based solar cells. The organic materials used in organic photo-voltaic

cells are the conjugated polymers with semi-conducting property as they tend to stimulate

an elementary system of converting radiative light energy into a useful current. The concept

of bulk hetero-junction (BHJ) in polymer solar cells have improved (in magnitude) the

interfacial area by the formation of an inter-penetrating network between the donor and

acceptor where the excitons competently dissociate in generating free electrons and holes.

Fig. 1: Regular OPV Cell (Efficiency ɳ = 1.77%)

Fig. 2: Inverted OPV cell (Efficiency ɳ = 3.66%)

Fig. 2: Inverted OPV module (Efficiency ɳ = 0.40%)

Fig.4: Final images of the OPV cells and modules.

Dye-Sensitized Solar Cells

C. Satish, E. Priyatha, K. Balachander & R. Venkateswaran

The dye sensitized solar cells (DSC) are currently the most efficient third-

generation technology. DSC is a photo electrochemical cell, which in principle

functions completely different than conventional solar cells. In certain respects, these

systems are designed to mimic the chlorophyll chromophore which is involved in the

conversion and storage of solar energy during photosynthesis in plants. In DSC, the

photon absorbing materials are needlessly a semiconductor, but highly colored dyes

which is attached to the nano structured TiO2 photo anode. A wide range of dyes has

been used for DSSC applications. In particular, research on novel ruthenium(II)

polypyridine complexes based dyes was increased due to its rich photophysical

properties such as intense absorption, long-lived lifetimes. DSC made a major

breakthrough in solar cell technology and has attracted considerable interest

because they are made of low-cost materials and can deliver good energy

conversion efficiencies.

Schematic diagram of DSC basic components

Perovskite Solar Cells

E. Priyatha, C. Satish, K. Balachander & R. Venkateswaran

Solar energy is a clean, abundant, and renewable energy source, and is regarded as

one of the best ways to solve the energy crisis and environmental pollution problem.

Perovskites solar cells (PSCs) are one of the hottest topics in photovoltaic field, offering

good power outputs from low-cost materials that are relatively simple to process into

working devices. The term perovskite is given to all compounds which have the general

chemical formula ABX3, and the crystal structure of calcium titanate (CaTiO3). In a typical

PSCs incoming light is absorbed by organic-inorganic perovskite material CH3NH3PbI3 that is

chemically attached to an n-type nanocrystalline titania framework. Upon light absorption,

perovskite material injects electrons into the conduction band of titania network. This is

followed by regeneration and subsequent hole transport through the hole transport

materials (HTM) to the respective electrode. The performance of PSC are limited by the

lengthy synthetic route and low hole mobility and conductivity of commonly used HTM

spiro-OMeTAD. In an effort to solve the problems, many new HTMS have been proposed to

improve the hole mobility and optimize HOMO levels. Our research group mainly deals with

the synthesis of novel HTMS and new perovskite material and tuning the each layer for the

device.

Schematic representation of Perovskite Solar Cells

Organic photovoltaic – Thin film photovoltaics is one of the important research area in

current scientific world. Among several technologies of thin film photovoltaics, organic

photovoltaics consists a large part and considered as immensely promising. Organic

photovoltaics deals with small molecules and polymer chains, but inherently these materials

have low charge mobilities and limited range of absorptivity. Generally a bulk heterojuntion

structure of organic solar cell has two materials in its active layer, electron donor and

acceptor. We are here studying the effect of tertiary add up molecules in increasing the

absorption edge as well as making a balance in mobilities of both kind of charges. This

would, we believe, enhance the efficiency of existing bulk heterojunction structure kind

organic photovoltaics.

S. Prathipkumar, Kallol Mohanta

Conductive fabric – Smart textiles are defined as textiles which can sense and react with

environment and stimuli. For this type of activity different types of sensors and actuators

(electronic, mechanical or magnetic) are deployed. Most of these sensors and actuators uses

electrical signal to sense and/or to make conversation within each other. Thus conductive

fabrics are necessary for this type of smart applications. We follow a simple and yet cost

effective procedure to make fabrics conductive and to be used for various purposes of

electronic and smart textile applications. Unlike other coating methods e.g. metallic layer

deposition painting conductive ink, the process we assumed should leave the fabrics

comfortable as well as highly conductive.

K. N. Ambasankar, Kallol Mohanta

Molecular array – Patterning of molecules in array induces extraordinary properties to the

assembly. The features of an arrayed pattern differ from random aggregation much like

crystalline properties differ from amorphous materials. But fabrication of a pattern or arrange

molecules in an array is difficult. We aim to develop thin films of arrayed molecules. The

molecules are arranged with the help of external field.

Sathiya M., Ranjitha K., Kallol Mohanta

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