Grätzel Photoelectrochemical Solar Cells From Sunlight to Electricity

Overview

i. Introduction to Grätzel Photoelectrochemical Solar Cells ii. How to make Grätzel solar cells iii. GCSE & AS/A-Level National Curriculum iv. GCSE & AS/A-Level

Investigations/Coursework

i. Introduction to Grätzel Photoelectrochemical Solar

Cells

Why Grätzel Photoelectrochemical Solar Cells?

Grätzel – Inventor Michael Grätzel and his researchers at Swiss Federal Institute of Technology in Switzerland

Photoelectrochemical – Electrochemical reactions involved (iodide electrolyte )

Solar – Absorption of sunlight energy in the visible region of the spectrum

First Published Paper

Brian O’ Regan & Michael Grätzel., Nature, A low cost, high efficiency solar cell based on dye sensitised colloidal TiO2 films, 353, 1991

What are Grätzel solar cell?

They are dye-sensitised titanium dioxide (TiO2) photo-

electrochemical cells that directly convert solar energy to electrical

energy

What do they look like?

1) Top Plate (-ve), Organic dye adsorbed onto a coated layer of TiO2 2) Bottom Plate (+ve), Coated with graphite

1 2

1 2

Grätzel Cell

Two conducting glass plates sandwiched together between iodide electrolyte

Schematic of Grätzel Solar Cell

TiO2 Layer

Dye adsorbed onto TiO2 particles

Iodide Electrolyte

Graphite layer

ITO conducting glass plate

ITO conducting glass plate

How do they work?....

e-

dye e-

e-

e-

I- I3-

e-

Solar Energy

(1)

(2) (3)

(4)

TiO2

Contd….. How do they work? 1) Sunlight energy (photoelectric effect) strike dye

molecules, exciting electrons 2) The excited electrons move through the conduction

band of TiO2 up to the conducting plate. Flow of electricity is initiated.

3) The dye is regenerated by the Iodide molecule giving up one of its electrons to form triiodide (oxidation occurs).

4) The triiodide molecule is reduced back to iodide by an electron at graphite conducting plate.

ii. How to make Grätzel solar cells

Steps to Making Grätzel Solar Cells

Step 1 & 2 - Preparation of plates Step 1 - + ve plate, coating with Graphite Step 2 - - ve plate, coating with TiO2 Step 3 - Adsorption of Dye onto TiO2 layer Step 4 - Assembly of Grätzel Solar Cell

Step 1 - Preparation of graphite plate (+ve)

Coated with Graphite

Using a Pencil

Uncoated Conductive Glass plate

Step 2 - Preparation of TiO2 plate (-ve)

1) Titanium dioxide powder and paste mix

2) Sintered @ 450 C for 30 minutes

(Pre-made TiO2 plates are also available)

Coated with TiO2

Uncoated Conductive Glass plate

Titanium Dioxide

Support material (10um thick) Large Surface Area (Nanoparticles ~30nm) High Porosity Electron acceptor Electron conductor Numerous Advantages (i.e. cheap, abundant, non -toxic)

Step 3 - Adsorption of Dye onto TiO2 coated plates

TiO TiO 2 2 coated plates adsorbing the dye

TiO TiO 2 2 coated plates Hybiscus tea leaves

boiled in water

Rinsed & Dried Rinsed & Dried

10mins 10mins

Organic dyes

Various organic dyes can be used…………….

Hybiscus Tea (supplied in kits) Ribena Turmeric Powder Tea Cranberries Onion Skin Raspberries

Step 4 - Assembly of Grätzel Solar Cell

Solar cell is made !!!!

Paperclip Clamp

(1)

(2)

Iodide Electrolyte

+ +

_

Electrolyte

Potassium Iodide Regenerates the Dye

D + (adsorbed on TiO2) + 3/2 I- D (adsorbed on TiO2) + 1/2 I3

-

I3- + 2e- 3I- At Cathode

Grätzel Cell Demonstration Kits

Each kit allows the students to prepare six solar cells to power a small electronic calculator

Website: www.mansolar.com

Power a Calculator

iii. GCSE & A-Level National Curriculum

GCSE - National Curriculum

Photosynthesis – How Grätzel solar cells use an analogous mechanism to photosynthesis for energy conversion

Energy - Renewable and Non Renewable Sources

Electricity – Ohms Law, Power, Electrical Circuits

i.e Photosynthesis & Solar Cells

SUN Chlorophyll

Hybiscus Tea

e- e-

e- e-

Electrical Energy

Chemical Energy

A-Level - National Curriculum

Biology: Photosynthesis – Use of an analogous mechanism to dye sensitised solar cells Physics: Electricity, Energy & Power

Chemistry: Redox Chemistry - The mechanism of energy conversion in solar cells Materials Chemistry - Substrates utilised for making solar cells Alternative Energy - Combustion and/or environmental chemistry UV- Vis Spectroscopy - Light Absorption Transition metal complexes - Dye molecules utilised

iv. GCSE & A-Level

Investigations/Coursework

GCSE – Lower Tier Investigations / Coursework

1. To investigate the effect of voltage on increasing the number of solar cells in a series/parallel circuit

2. To investigate the effect of voltage/current on using different organic dyes

GCSE- Higher Tier Investigations / Coursework

1. To investigate the power output (P=IV) of Grätzel

Solar cells on

i. varying the number of solar cells in a series/parallel circuit

ii. using different types of light bulbs for illuminating the solar cells (halogen, incandescent and fluorescent)

iii. using various soaking times for adsorbing the dye onto the TiO2

iv. varying the intensity of light

Biology - A-level Investigations / Coursework

To compare the mechanisms of energy conversion in photosynthesis and Grätzel solar cells and investigate the effects of power efficiencies using chlorophyll and other related organic/inorganic dyes in Grätzel solar cells

Physics & Chemistry - A-level Investigations / Coursework

1. To investigate the power efficiency of Grätzel solar cells using

a. Various soaking times for adsorbing the dye onto TiO2

b. Various light intensities c. Various organic/inorganic dyes d. Various types of TiO2 based materials (i.e. toothpaste, paint) e. Various coloured lights