3 Alternative photovoltaic concepts and photovoltaic systems

• 1st: Solar cells (today 95% of the world market)

  made of polycrystalline or monocrystalline

  silicon (indirect semiconductor), cells are

  connected to form modules.

• 2nd: Thin film solar cells (e.g. amorphous silicon,

  CdTe, CIS, ...), direct semiconductors,

  production by evaporation and direct structuring

  to modules.

• 3rd: Solar cells with "photon management",

  either multiple cells mechanically or

  monolithically stacked on top of each other

  with different band gaps or "photon

  recycling" by up- or down conversion.

thin film 10 GWP

Multi-Si 20

Mono-Si 160

von thin: CdTe>CIGS>a-Si

• In contrast to crystalline silicon, a-si is a direct semiconductor.

• Efficiency stabilizes itself during operation

■ Copper Indium Gallium Diselenide

■ Laboratory cell efficiency: 22.9%

■ Module efficiency: 14.5%

■ Advantages:

□ Environmentally friendly

□ Greater heat resistance

□ Long lifecycle

■ Disadvantage:

□ High manufacturing costs

■ Cadmium-Telluride

■ 43% Market share of thin-film PV

■ Laboratory cell efficiency: 22.1%

■ Module efficiency: 16.1%

■ Advantages:

□ Simple and cost-effective

manufacturing process

□ Cadmium ist abundant

□ Good low-light performance

□ Good temperature behaviour

■ Disadvantages:

□ Cadmium is toxic

□ Telluride is a rare material

■ Copper-Zinc-Tin sulphide

■ Laboratory cell efficiency: 12.6%

■ Advantages:

□ All materials used are non-toxic and

abundant

□ Low manufacturing costs

■ Disadvantages:

□ Low efficiency

□ Lack of knowledge of electrical and

chemical properties of the material

Photoactive material of organic molecules or conductive

polymers based on C-H

■ Donor acceptor system comprising a transparent

electrode (ITO) and a metallic counter electrode

Donator: CN-PPV, P3HT, MEH-PPV

■ Functions: light absorption, emission of an electron,

transport of the hole to the cathode

Acceptor: Fullerene C60, C70

■ Function: electron uptake and transport to the anode

■ Very thin cells (approx. 0.1μm)

■ Photo-electrochemical system, also called Grätzel cell

(name of the inventor)

■ Light absorption takes place in organic dyes

(e.g. ruthenium-based or chlorophyll)

■ Dyestuffs deposited on highly porous carrier material

(TiO2, ZnO, SnO2), resulting in increased effective

surface area

■ Good low-light performance

■ Efficiencies at 12% (cell) and 8% (module)

Stacking two solar cells: Tandem cells

• → Efficiency is significantly increased

  • Light is absorbed at different depths

  depending on wavelength

  • Cells connected in series: weaker cell

  determines total current

Triple cells

• Stabilized efficiencies of 38 % were achieved

  Staebler-Wronski effect very low

Micromorph = microcrystalline + amorphous

• Stable efficiencies Laboratory cells: 12%, modules: max. 10%

• requires the least amount of energy for

  production

• semiconductor materials

  • Amorphous Silicon (a-Si)

  • Gallium Arsenide (GaAs)

  • Copper Indium Gallium Selenide (CIGS)

  • Cadmium Telluride (CdTe)