Solar Technology Today
Photovoltaic power can be produced in many ways, with widely varying efficiency and costs. They can be divided into two basic groupings: discrete cell technology and integrated thin film technology.
 

Discrete Cell Technology

Single-crystal silicon  
Sliced from single-crystal boules of grown silicon, these wafers/cells are now cut as thin as 200 microns. Research cells have reached nearly 24-percent efficiency, with commercial modules of single-crystal cells exceeding 15-percent.

Multicrystalline silicon
Sliced from blocks of cast silicon, these wafers/cells are both less expensive to manufacture and less efficient than single-crystal silicon cells. Research cells approach 18-percent efficiency, and commercial modules approach 14-percent efficiency.

Edge-defined film-fed growth ribbons
Nearly single-crystal silicon ribbons grown from a crucible of molten silicon, drawn by capillary action between the faces of a graphite die.

Dendritic web
A film of single-crystal silicon pulled from a crucible of molten silicon, like a soap bubble, between two crystal dendrites.

Gallium Arsenide (GaAs)
A III-V semiconductor material from which high-efficiency photovoltaic cells are made, often used in concentrator systems and space power systems. Research cell efficiencies greater than 25 percent under 1-sun conditions, and nearly 28 percent under concentrated sunlight. Multijunction cells based on GaAs and related III-V alloys have exceeded 30-percent efficiency.

Integrated Thin Film Technology

Copper Indium Diselenide (CuInSe₂, or CIS)
A thin-film polycrystalline material, which has reached a research efficiency of 17.7 percent, delivers the highest completed module efficiency for full sized power modules, reaching over 11 percent.

Amorphous Silicon (a-Si)
Used mostly in consumer products for solar watches and calculators, a-Si technology is also used in building-integrated systems, replacing tinted glass with semi-transparent modules. The primary issue with a-Si technology remains the low efficiency and associated greater requirement for space and higher array installed cost and weight

Cadmium Telluride (CdTe)
A thin-film polycrystalline material, deposited by electrodeposition, spraying, and high-rate evaporation.Small laboratory devices approach 16-percent efficiency, with commercial-sized modules (7200-cm²) measured at 8.34-percent (NREL-measured total-area) efficiency and production modules at approximately 7 percent.

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Advantages of Photovoltaic Power