This document summarizes the three generations of solar cells and discusses cadmium telluride (CdTe) solar cells in more detail. The three generations include first generation wafer-based silicon cells, second generation thin-film technologies like CdTe and CIGS, and third generation low-cost high-efficiency cells. CdTe solar cells have advantages over silicon cells like a direct bandgap matching the ideal value for efficiency. Research is ongoing to boost CdTe cell efficiencies further and address challenges like tellurium supply and long-term degradation.

1. Advancement of Solar Cell
SUBHASIS SHIT
17PH62R17
Indian Institute of Technology, Kharagpur
M.Tech 1st Year

2. 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

3. 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%

4. 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).

5. 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).

6. Cell Configuration: Superstrate & Substrate
Efficiency: 11-
12%
Efficiency: <
2%

7. 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%.

8. 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

9. 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.

10. 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.

11. THANK YOU