ASeminar

On“Carbon Nanotube Based Solar Cell”

Submitted to: Submitted By: Supervisor Mohammad Safil BegDeepak Bhatia 14E2CNNTX3XP704Assistant Professor

 Centre of NanotechnologyRajasthan Technical University, Kota

December -2015  

Carbon Nanotube Based Solar Cell

Outline• Introduction

• Carbon Nanotubes

• Properties for CNTs

• Efficiency Limiting Factors

• Nanotubes in Solar Cell

• Conclusion

Introduction• Carbon nanotubes (CNTs) are allotropes of carbon with a

cylindrical nanostructure.

• Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene.

• These sheets are rolled at specific and discrete angles.

Carbon Nanotubes• S. Iijima - MWNT (1990), SWNT (1993)

• Rolled graphene sheet with end caps

• Large aspect ratios

• Unique properties

How CNT are made.

Synthesis Methods1. Arc Discharge Method. 2. Laser Ablation Method. 3. Chemical Vapour Deposition

Method.

1.Arc Discharge Method • CNT can be found in the carbon soot of

graphite electrodes during an arc discharge

involving high current.

• SWNT Diameter=1.1 to 1.4 nm.

• Inner Diameter of the MWNTs

varies in the range 1 to 3 nm.

• Outer Diameter MWNT varies

in the range of 2 to 25 nm.

Properties for CNTs 1. Electrical Properties.

2. Transport Properties.

3. Mechanical Properties.

• If the nanotube structure is armchair then the electrical properties are metallic.

• If the nanotube structure is chiral then the electrical properties can be either semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor.

Electrical Properties

A CNT is characterized by its Chiral Vector: Ch = n â1 + m â2, Chiral Angle

a) Armchair (n=m) f.e. (5,5) = 30b) Zig Zag (n=0,m≠0) f.e (9,0) = 0c) Chiral (n≠0,m≠0) f.e (10,5)0 < < 30

(a)

(b) (c)

One-Dimensional Transport• Due to their nano scale in CNT will take place though quantum effects and will only propagate along the axis of the tube, because of this special transport property, CNT are frequently referred to as one dimensional.

Mechanical Properties• Very high strength,

• Modulus, and resiliency.

• Good properties on both compression and extension.

Three generations of solar cells

First Generation

• First generation cells consist of large-area, high quality and single junction devices.

• First Generation technologies involve high energy and labour inputs which prevent any significant progress in reducing production costs.

PROBLEMS :

• Single crystalline silicon efficiency of ~ 15-16%.• The module life is about 25 years.• Polycrystalline silicon solar cells efficiency ~12-14% .

Cont.

Second Generation

• Second generation materials have been developed to address energy requirements and production costs of solar cells.

• Alternative manufacturing techniques such as vapour deposition and electroplating are advantageous as they reduce high temperature processing significantly

• Thin film silicon (amorphous silicon)• CdTe (Cadmium Telluride)• CuInSe2 (Copper Indium Diselenide)

Cont.

PROBLEMS : • Thin Film deposition throughput limited to 2-3 microns / min which is not cost effective Higher throughput with good quality opto-electronic properties required Photon trapping structures , Passivation and Cheap Substrate required for lowering the cost . • Module Efficiency : ~ 10%

Third Generation

• Dye-sensitized solar cell• Metal based dye-sensitized solar cell• CNT based dye-sensitized solar cell

CNT based dye-sensitized solar cell• Dye sensitized solar cells (DSSCs) are a relatively

new class of thin film solar cells with promising high conversion efficiency at a low cost.• These solar cells utilize two main components a

photo anode consisting of light absorbing dye molecules adsorbed on a semiconductor material, and an electrically conductive counter electrode.• In a typical thin film solar cell, the electrodes are

made of conductive metals and Indium tin oxide. Materials like indium are scarce and becoming more expensive as the demand of solar cell increases.

• Carbon based transparent electrodes as the replacement of conventional FTO/ITO have been widely used in several solid-state opto- electronic devices such as organic thin film transistors, organic light emitting diodes.• Because of the low cost, high durability, excellent

catalytic activity, and electrical conductivity, carbon-based materials have been utilized as effective alternative counter electrode for many years.• It came to our attention that the dramatically reduced

cost and high stability of DSSCs could be achieved if FTO/ITO and Pt in DSSCs are replaced with carbon based materials at both working and counter electrode.

Working of CNT based DSSC• The transferred N-CNTs

and the DSSC unit cell with N-CNT counter electrodes are shown in Fig.

• The DSSC fabricated with an N-CNT counter electrode had a slightly higher fill factor of 0.67 and a Jsc of 14 mA cm-2 .

• A Voc of 0.767V, and a conversion efficiency of 7.04%.

Cyclic voltammograms of the N-CNTs on the ITO substrate and the Pt on the FTO substrate.

• N-CNT counter electrode exhibited nearly the same peak positions as the Pt counter electrode. The cathodic and anodic peak current densities of the N-CNT counter electrode were much higher than those of the Pt electrode.• The N-CNT counter electrode exhibits higher

electrochemical activity, which indicates that there is a much faster reaction rate on the N-CNTs and electron transfer rate from the substrate to the N-CNTs.

• The transferred N-CNT film was tested for use as a counter electrode for DSSCs, resulting in a power conversion efficiency of 7.04%, while that of a reference DSSC with a conventional Pt/TCO counter electrode was 7.34%.

• We also demonstrated that our method is useful for constructing flexible DSSCs. Overall, our approach involving N-CNTs offers a promising route to low-cost and substrate-independent Pt-free counter electrodes for DSSCs.

Conclusion

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Thank you