SOLAR CELL FABRICATION

IC TechAssignment

Group :-• Saikat Saha• Shomik Biswas• Tirthankar Mittra

Solar Cell

Fabrication

INTRODUCTION AND BRIEF

HISTORY

What is a Solar Cell ?

A Structure that converts solar energy directly to DC Electric energy

Acts like a battery because it supplies DC Power

It is different from the battery in the sense that the voltage supplied by the cell changes with the changes in the resistance of the load.

Basic Physics of Solar Cells

Silicon (Si) is from group 4 of the periodic table. When many Si atoms are in close proximity, the energy states form bands of forbidden energy states.

One of these bands is called the Band Gap (Eg) and the absorption of light in Si is a strong function of Eg.

Si is covalently bonded. It shares electrons. When a Si atom is replaced with a group 3(Al, B) it forms a positive particle called hole that can move around the crystal through diffusion or drift (electric field).

When a Si atom is replaced with a group 5 (As, P) it forms an electron that can move around the crystal.

Because we can selectively dope a Si crystal it is called a semiconductor.

By selectively doping the Si Crystal we can change the resistivity and which type of carrier transfers charge (carries current).

Basics of Solar Cells

If two differently contaminated semiconductor layers are combined, then a so-called p-n-junction results on the boundary of the layers.

By doping trivalent element, we get p-type semiconductor. (with excess amount of hole).

By doping pentavalent element, we get n-type semiconductor ( with excess amount of electron).

Definition :-

The generation of voltage across the

PN junction in a semiconductor due to the absorption of

light radiation is called photovoltaic effect. The Devices based on this effect

are called photovoltaic

devices.

PHOTO- VOLTAIC EFFECT

Photovoltaic effect is the basis of photo voltaic power generation.

History of Solar

Cell

History of Solar

Cell

In 1883, first photo voltaic cell was made by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions.

It was only 1% efficient.

A solar cell is a junction (usually a PN junction) with sunlight shining on it.

The first practical photovoltaic cell was developed in 1954 at Bell Laboratories .They used a diffused silicon p–n junction that reached 6% efficiency, compared to the selenium cells.

Most practical solar cells are silicon based , because it is cheap and abundant material.

The Solar Dudes

April, 1954; Bell Labs, Murray Hill (NJ).

(R to L) Gerald Pearson, Daryl Chapin, Calvin Fuller

Types of

Solar cell

Based on the types of crystal used, solar cells can be classified as --

• Monocrystalline silicon cells

• Polycrystalline silicon cells

• Amorphous silicon cells

Based on the types of crystal used, solar cells can be classified as --

Based on the types of crystal used, solar cells can be classified as :-

Monocrystalline solar cells are made from a very pure type of silicon. More the purity, more efficient the material is. They are also the most space-efficient. They also last the longest of all types. This superiority comes with a price tag.

The efficiency of amorphous cells is much lower than that of the other two cell types. As a result, they are used mainly in low power equipment, such as watches and pocket calculators, or as facade elements.

Amorphous silicon is obtained by depositing silicon film on the substrate like glass plate. The layer thickness amounts to less than 1µm – the thickness of a human hair for comparison is 50-100 µm.

It is less efficient than its monocrystalline cousin because of less purity of the material. It is less space-efficient. It also has a lower heat tolerance than monocrystalline.

Polycrystalline solar cells, were the first solar cells ever introduced to the industry, in 1981. They're much more affordable since hardly any silicon is wasted during the manufacturing process.

Comparison of Types of solar cell

Material Efficiency (%)

Monocrystalline silicon 14-17

Polycrystalline silicon 13-15

Amorphous silicon 5-7

SOLAR CELL FABRICATION PROCEDURE

Part I: Wafer Cleaning

Procedure

Wafer Before Cleaning

Wafer After Cleaning

Part II: First Oxide

Deposition

Wafer with 100nm oxide growth.

Part III: Thin Photoresist

Application and First Mask

Pattern Transfer

Wafer after application of 1808 photoresist.

Development of the 1st Mask Patterned Wafer

Wafer after development of First Mask

Removal of SiO2 using buffered HF etching

Wafer with Patterned Oxide Layer

Part IV: Photoresist

Removal and KOH etching

Wafer after photoresist removal.

Oxide Removal with Buffered HF

Silicon Wafer with KOH etching and Oxide Layer Removed

Part V:Ion Implantation of n-dopant

(phosphorus)

Wafer after phosphorus and boron ion implantation.

Part VI: Growth of

Anti-Reflective

Oxide Layer

Wafer after second oxide growth.

Part VII: Photoresist Application

for Rear Contact

Removal of SiO2 using buffered HF etching from the rear side.

Part VIII: Aluminum deposition onto the back side

of the wafer

Removal of native oxide using buffered HF etching

Removal of 2 inch wafer from 4 inch wafer

Part IX: Thick Photoresist

Application and Third Mask

Pattern Transfer

Wafer After Third Photoresist Application.

Part X: Aluminum Deposition and Lift-off

Wafer after Aluminum Deposition

Part XI: Final

Annealing Step

Final Solar Cell

What Now ?

The Current Scenario

Production of fossil fuels is expected to rise.

As world population continues to grow and the limited amount of fossil fuels begins to diminish, it may not be possible to provide the amount of energy demanded by the world by only using fossil fuels.

The fairly low cost of converting natural resources to energy causes most countries to use fossil fuels as their main source of energy

As natural resources are limited and non-renewable so it gives rise to a major problem.

There is only so much oil, coal, and natural gas that the earth can hold, and we cannot use these resources as if there is an unlimited amount for much longer.

The increasing trend in world energy use can be attributed to two main reasons: a growing world population and developing countries.

More people means more energy consumption, and if we stick to fossil fuels as the major resource, means less time until we run out of fossil fuels.

A major reason for countries not adopting the technologies of these renewable resources is the cost.

While it is almost sad to think that we are too worried about short-term monetary costs to invest in these technologies

Rather than avoiding the even larger costs that a dramatic climate change or international economic crisis would bring.

Uses And Applications

Solar Powered Farms

Off Grid Power

Rooftop Solar Panels

Space Equipment

Renewable Energy

What Next ?

The world needs to accept the reality and start acting accordingly. There are ongoing largescale efforts in making solar energy viable to the masses.

Elon Musk through his company SolarCity is spreading awareness about the long term advantages of solar energy and distributing solar panels to households on a lease based system.

Power Wall 2

Solar Roof Tiles

Tommy Hilfiger have launched a clothing range which has flexible solar panels incorporated with the fabric.

The solar energy available in space is

literally billions of times greater than we use today. Americans

and Japanese are working on this project to gather energy from sunlight in space and transmit it wirelessly

to Earth.

These were some of the progressions made using the technology, but there needs to be a paradigm shift in the way this issue is being handled to make it work.

This Presentation was created by :- Saikat Saha, Shomik Biswas and Tirthankar MittraFor an assignment on the topic :- Solar Cell Fabrication

Done under Prof. Nirmoy Modak, JU

Thank You