Solar Cell

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very useful prof deshmukh

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Slide 1: 

Dr A. Kathu MINT Dongguk University Dye Sensitized solar cell

For Information : 

For Information NAME-QUAM-Nanodesigning of atomic and molecular quantum matter, EU funded project for 'Information and communication technologies‘ Its aim is to identify new directions and alternative approaches towards scalable and miniaturisable quantum information processing using quantum-matter technology ( ultracold atom and molecules), it has developed an exotic mater wherein atoms are aligned in one dimensional structure "Quietest" building in the world opened on 7 Sep 2009, It is a research centre (NSQI-Nanoscience and Quantum Information-University of Bristol), state-of-the-art specialised laboratories where vibration and acoustic noise levels are among the lowest ever achieved.

Background : 

Background 3rd energy-crisis is coming Devastating fossil fuels Green-house effect is deteriorating Renewable, cheaper, environment friendly energy is in highly needed The sun provides a nearly unlimited energy resource, but existing solar energy harvesting technologies are prohibitively expensive and cannot compete with fossil fuels." Demanding !

Evolution of Solar Cell Devices : 

Evolution of Solar Cell Devices Combination of biological and inorganic (metal oxide) components to create solar cell

Efficiency of Different Cells : 

Efficiency of Different Cells

Overview of solar cells : 

Overview of solar cells First Generation Single crystal silicon wafers (c-Si) Second Generation Amorphous silicon (a-Si) Polycrystalline silicon (poly-Si) Cadmium telluride (CdTe) Copper indium gallium diselenide (CIGS) alloy Third Generation Nanocrystal solar cells Photoelectrochemical (PEC) cells • Gräetzel cells Polymer solar cells Dye sensitized solar cell (DSSC) Fourth Generation Hybrid - inorganic crystals within a polymer matrix

First Generation (Silicon) : 

First Generation (Silicon) First generation photovoltaic cells are the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market Cells are typically made using a crystalline silicon wafer Consists of a large-area, single layer p-n junction diode Band gap ~1.11 eV Disadvantages Requires expensive manufacturing technologies Much of the energy of higher energy photons, at the blue and violet end of the spectrum, is wasted as heat

Second Generation ( Thin-films) : 

Second Generation ( Thin-films) Based on the use of thin-film deposits of semiconductors Using of thin-films reduces mass of material required for cell design Contributes greatly to reduced costs for thin film solar cells Several technologies/semiconductor materials currently under investigation or in mass production Deposition of thin layers of non-crystalline-silicon materials on inexpensive substrates using PECVD Devices initially designed to be high-efficiency, multiple junction photovoltaic cells

Second Generation: Types : 

Second Generation: Types 1. Amorphous silicon cells deposited on stainless-steel ribbon, Can be deposited over large areas by plasma-enhanced chemical vapor deposition (Band gap ~ 1.7 eV) 2. Polycrystalline silicon, Consists solely of crystalline silicon grains (1mm), separated by grain boundaries ( Band gap ~1.1eV) 3. Cadmium telluride (CdTe) cells deposited on glass (Band gap ~ 1.58 eV) 4. Copper indium gallium diselenide (CIGS) alloy cells (Band gap ~ 1.38 eV)

Second Generation : 

Second Generation Advantages Lower manufacturing costs ,Lower cost per watt can be achieved Reduced mass, Less support is needed when placing panels on rooftops Allows fitting panels on light or flexible materials, even textiles Disadvantages Typically, the efficiencies of thin-film solar cells are lower compared with silicon (wafer-based) solar cells Amorphous silicon is not stable Increased toxicity

Third Generation : 

Third Generation Very different from the previous semiconductor devices Do not rely on a traditional p-n junction to separate photogenerated charge carriers Devices include: Nanocrystal solar cells Photoelectrochemical cells Gräetzel Cell Dye-sensitized hybrid solar cells Polymer solar cells

Third Generation: Types : 

Third Generation: Types 1. Nanocrystal solar cells Solar cells based on a silicon substrate with a coating of nanocrystals Silicon substrate has small grains of nanocrystals, or quantum dots • Lead selenide (PbSe) semiconductor • Cadmium telluride (CdTe) semiconductor Quantum dot is a semiconductor nanostructure Confines the motion of conduction band electrons, valence band holes, or excitons in all three spatial directions Thin film of nanocrystals is obtained by a process known as “spincoating”

Third Generation: Types : 

Third Generation: Types 2. Photoelectrochemical (PEC) cells Separates the two functions provided by silicon in a traditional cell design Consists of a semiconducting photoanode and a metal cathode immersed in an electrolyte In the interface of electrolyte and semiconductor is used for charge seperation by the associated activity of semiconductor and electrolyte Charge conduction takes place by semiconductor and electroly

Third Generation: Types : 

Third Generation: Types 3. Dye-sensitized PEC cells ( Gräetzel cells) Semiconductor solely used for charge separation Photoelectrons provided from separate photosensitive dye Overall peak power production represents a conversion efficiency of about 11% Cell Design: Dye-sensitized titanium dioxide Coated and sintered on a transparent semi-conducting oxide (ITO) For hole conduction and regeneration of dye, electrolytes or polymeric conductors are used Different designs are available based on the type of electrolyte and organic ionic conductors (conductive polymer) used

Third Generation: Types : 

4. Polymer solar cells Bulk heterojunctions between an organic polymer and organic molecule as electron acceptor. Fullerene embedded into conjugated polymer conductor Lightweight, disposable, inexpensive to fabricate, flexible, designable on he molecular level, and have little potential for negative environmental impact. Present best efficiency of polymer solar cells lies near 5 percent Cost is roughly one-third of that of traditional silicon solar cell technology ( Band gaps ≥ 2eV) Third Generation: Types

Slide 17: 

The scheme of plastic solar cells. PET - Polyethylene, ITO - Indium tin Oxide, PEDOT:PSS - [[Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), Active Layer (usually a polymer:fullerene blend), Al -Aluminium

Third Generation : 

Third Generation Advantages Low-energy, high-throughput processing technologies Polymer cells - solution processable, chemically synthesized Polymer cells - low materials cost Gräetzel cells - attractive replacement for existing technologies in “low density” applications like rooftop solar collectors Gräetzel cells - Work even in low-light conditions DSSC - potentially rechargeable => upgradeable? Disadvantages Efficiencies are lower compared with silicon (wafer-based) solar cells Degradation effects: efficiency is decreased over time due to environmental effects PEC cells suffer from degradation of the electrodes from the electrolyte

Fourth Generation : 

Fourth Generation Hybrid - nanocrystal/polymer cell Composite photovoltaic technology combining elements of the solid state and organic PV cells Use of polymers with nanoparticles mixed together to make a single multispectrum layer Significant advances in hybrid solar cells is the elongated nanocrystal rods and branched nanocrystals gives more effective charge transport

Fourth Generation : 

Fourth Generation Cell Design: Solid state nanocrystals (Si, In, CuInS2, CdSe) Imbedded in light absorbing polymer (P3HT) p-type, polymeric conductor, such as PEDOT:PS, carries ‘holes’ to the counter electrode Coated on a transparent semi-conducting oxide (ITO)

Fourth Generation: Future : 

Fourth Generation: Future Thin multi layers can be stacked to make multispectrum solar cells Different layers convert different parts of the light is first It take advantages of converting full spectrum from UV to IR It could convert some of the heat radiation also More efficient and cheaper Based on polymer solar cell and multi junction technology Future advances will rely on new nanocrystals, such as cadmium telluride tetrapods and PdS etc. Potential to enhance light absorption and further improvement of charge transport. Gains can be made by incorporating application-specific organic components, including electroactive surfactants which control the physical and electronic interactions between nanocrystals and polymer

Fourth Generation: Evaluation : 

Fourth Generation: Evaluation Advantages Solution processable Lower materials cost (polymer) Self-assembly Printable nanocrystals on a polymer film Improved conversion efficiency (potentially) Disadvantages Efficiencies are lower compared to silicon (wafer-based) solar cells Potential degradation problems similar to polymer cells Optimize matching conductive polymers and nanocrystal

Slide 23: 


Dye-Sensitized Solar Cell (DSSC) : 

Dye-Sensitized Solar Cell (DSSC) Semiconductor Sensitizer Electrolyte

Three important components in solar cells : 

Three important components in solar cells Cost Size Efficiency Electrolyte Photoelectrode

Schematic of DSSC : 

Schematic of DSSC Graetzel

DSSC Principle : 

DSSC Principle Dye-sensitized solar cells operate differently from other types It is similar to the natural process of photosynthesis ( artificial photosynthesis) Like the chlorophyll in plants, a monolayer of dye molecules (sensitizers) absorbs the incident light, generates positive and negative charge carriers The charge carriers are efficiently transported to the electrodes

Slide 28: 


Photoconversion process : 

Photoconversion process Upon light absorption, the dye (S) is promoted into an electronically excited state (S∗) It injects an electron into the conduction band of a large band gap semiconductor film (TiO2) within femto seconds These electrons are transported through the TiO2 film by diffusion and reaches the SnO2:F coated anode and to the external circuit The positive charges(S+) resulted are transferred into a liquid electrolyte and it is reduced by a redox couple in the electrolyte solution This leads to the regeneration of the charge neutral state of the sensitizer After ionic diffusion, the carrier of the positive charge reaches the cathode, where it releases its charge , reduced to neutral This process typically requires a catalytic material on the cathode surface , so Pt is used in the cathode

Photoconversion process : 

Photoconversion process The overall photoconversion process is regenerative; there is no net change in the chemical composition of the cell The key to efficient light harvesting is the high surface area of the porous TiO2 film The single monolayer of dye molecules on a flat TiO2 film can typically absorb all the fraction of the incoming light Nanostructured TiO2 films provide enough surface area for more dye monolayers adsorption Open porosity of these films allows the liquid electrolyte to fill all pores of the film The nanocomposite geometry ascertains contact of every dye molecule to both the TiO2 and electrolyte

Photoconversion process : 

Photoconversion process Unlike any other type of solar cells, charge generation takes place at the interface, the TiO2/dye/electrolyte interface Also, the processes of light absorption and charge transport are separated The dye molecules only absorb the light and generate the charge carriers, while charge transport occurs in the TiO2 and the electrolyte This implies the absence of minority carrier recombination, and hence a relatively high tolerance for impurities

Requirement of Photosensitiser : 

Requirement of Photosensitiser An efficient photosensitizer should fulfill some requirements such as An intense absorption in the visible region Strong adsorption onto the semiconductor surface Efficient electron injector into the conduction band of the semiconductor Moreover, it must be rapidly regenerated by the mediator layer in order to avoid electron recombination processes Must be fairly stable, both in the ground and excited states Charge must be rapidly separated to prevent back reaction

DSSC based Tandem Solar Cell for High Efficiency : 

DSSC based Tandem Solar Cell for High Efficiency Efficiency of present DSSC is about 11.3% Liska et all (App Phys Lett) has produced efficiency of 15% for a cell comprising of DSSC as top cell for high energy photons and CIGS thin film bottom cell capturing red and near IR If optimized for electron transport, current matching and optical losses it could produce more than 15 % also

Lower-cost solar cells to be printed like newspaper, painted on rooftops : 

Lower-cost solar cells to be printed like newspaper, painted on rooftops Solar cells could soon be produced more cheaply using nanoparticle "inks" (Korgel's research ) It can be printed like newspaper or painted onto the sides of buildings or rooftops to absorb electricity-producing sunlight Nanopillars could spell cheaper, more efficient solar cells Arrays of CdS nanoscale pillars could produce cheaper and more efficient solar cells [Z. Fan et al., Nature Materials (2009)] Unlike conventional two-dimensional solar cells, the nanopillar array offers a much larger surface area for collecting light. These structures improve the collection and separation of photocarriers, boosting the overall energy conversion efficiency of devices.

To Improve Efficiency : 

To Improve Efficiency

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