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
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.
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.
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.