Advancement of Solar Cell

SUBHASIS SHIT

17PH62R17

Indian Institute of Technology, Kharagpur

M.Tech 1st Year

Solar Cells- Three Generations

1st Generation: ‘Wafer’ based

Monocrystalline silicon

Polycrystalline silicon

Multi-junction cell (different band-gap material)

2nd Generation: ‘Thin film’ based

Amorphous thin film silicon

CdTe (Cadmium Telluride)

CIGS (Copper Indium Gallium Selenium)

3rd Generation: Low cost and high efficient

DSSC (Dye-sensitized solar cells)

QDSSC (Quantum Dot-sensitized solar cells)

OPV (Organic photovoltaic)

Perovskite Solar Cells

Conventional Si Solar Cells: Productions & Limitations

Indirect bandgap with less bandgap energy 1.12ev.

Thickness of the wafers is more, about 160 – 240 mm.

Total process time of manufacture is near about 30

hours.

Production cost is high.

Efficiency :

25%

Advantages of CdTe Solar Cell over C-Si Solar Cell

CdTe has direct bandgap with bandgap energy 1.46 ev which is very much close

to the ideal value for photovoltaic conversion efficiency

Optical absorption coefficient (104 cm-1) and chemical stability is high.

The cell thickness is very less nearly 2-3 microns.

The manufacturing time is also very less nearly about 20 mins.

Easy of manufacturing.

Lower capital cost and labour cost ($0.85/Wp).

CdTe Solar Cell: Schematic Diagram

A simple p-n heterojunction structure containing p-doped CdTe layer

matched with n-doped CdS layer.

It has high quality transparent conductive oxide (TCO) – usually fluorine

doped tin oxide (SnO2:F).

Back electrical contact typically a metal or carbon paste with copper (Cu).

Cell Configuration: Superstrate & Substrate

Efficiency: 11-

12%

Efficiency: <

2%

Efficiency of CdTe Solar Cell

In 2013 the conversion efficiency of labscale solar cell as obtained

by ‘First Solar’ was 18.7% . The Voc was 852 mv and Jsc was

nearly 28.6 mAcm-2 with FF 76.76%.

At that year NREL confirmed the efficiency nearly about 16.1%.

Cell efficiency achieved by ‘First Solar’ in 2016 February was

22.1%.

Concerns: Toxicity

CdTe solar cells contain Cd, one of the six deadliest toxic materials, but

insoluble Cd compounds like CdTe, CdS are much less toxic.

CdTe solar cell is more environmental friendly than all other uses of Cd.

Recycling schemes have been installed for CdTe solar modules

Challenges of CdTe Solar Cells

Tellurium supply: While Cadmium is relatively abundant, Tellurium is not.

Tellurium (Te) is an extremely rare element (1-5 parts per billion in the Earth's

crust). Most of it comes as a by-product of copper, with smaller byproduct

amounts from lead and gold.

Recently, researchers have added an unusual twist – astrophysicists identify

tellurium as the most abundant element in the universe with an atomic number

over 40. Researchers have shown that well-known undersea ridges (which are

now being evaluated for their economic recoverability) are rich in tellurium and

by themselves could supply more tellurium than we could ever use for all of our

global energy. It is not yet known whether this undersea tellurium is

recoverable, nor whether there is much more tellurium elsewhere that can be

recovered.

Ongoing Research

Research on CdTe research focuses on several of today's challenges:

1. Boosting efficiencies by, among other things, exploring innovative

transparent conducting oxides that allow more light into the cell to be

absorbed and that collect more efficiently the electrical current generated

by the cell.

2. Studying mechanisms such as grain boundaries that can limit the

voltage of the cell.

3. Understanding the degradation that some CdTe devices exhibit at

contacts and then redesigning devices to minimize this phenomenon.

4. Designing module packages that minimize any outdoor exposure to

moisture.

5. Engaging aggressively in both indoor and outdoor cell and module

stress testing. For example, we propose to test thin-film modules in hot

and humid climates.

THANK YOU