The

portmanteau In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together.

micromorph is a combination of the words microcrystalline and amorphous. It is used for a type of silicon based

multijunction Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p–n junction will produce electric current in response to different wavelengths of light. The use of mult ...

thin-film solar cell Thin-film solar cells are a type of solar cell made by depositing one or more thin layers (thin films or TFs) of photovoltaic material onto a substrate, such as glass, plastic or metal. Thin-film solar cells are typically a few nanometers (nan ...

The micromorph cell

Micromorph cells are

thin film solar cell Thin-film solar cells are a type of solar cell made by depositing one or more thin layers (thin films or TFs) of photovoltaic material onto a substrate, such as glass, plastic or metal. Thin-film solar cells are typically a few nanometers ( nm ...

s based on a

–architecture consisting of two

solar cell A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect.

s that are stacked on top of each other. While the thin

amorphous silicon Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs. Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films onto ...

top cell absorbs the blue light, the thicker microcrystalline silicon bottom cell absorbs the red and near-infrared light, allowing this so-called tandem cell to cover a wider range of the

solar spectrum Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible light perceptible to the human eye as well as invisible infrared (typically perc ...

. Since the bandgaps of amorphous silicon (1.7eV) and microcrystalline Silicon (1.1eV) are well suited for tandem solar cells, the Shockley-Queisser limit of this cell allows conversion efficiencies of over 30%. In reality this limit can not be reached and typical stable efficiencies are about 9% (world record 11.7%). That is well over the stable efficiencies of single junction thin film silicon solar cells which are around 6%. One reason of the low costs of silicon thin film solar cells is its very low thickness (2 μm) compared to

silicon wafer In electronics, a wafer (also called a slice or substrate) is a thin slice of semiconductor, such as a crystalline silicon (c-Si, silicium), used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The ...

(200 μm). In the red and infrared wavelength range 2 μm of silicon are not enough to absorb all light and therefore 'light trapping' is needed. The advantage of the micromorph approach is that it keeps the thickness of the amorphous top cell low. This reduces the effect of degradation induced by light ( Staebler-Wronski effect). In multijunction cells top and bottom cell have to produce the same current. But the top cell is limited by the Staebler-Wronski effect and therefore light trapping and an intermediate reflector are needed to keep the thickness of the top cell low while increasing its current.

The intermediate reflector

The intermediate reflector is a layer (IRL) of

zinc oxide Zinc oxide is an inorganic compound with the Chemical formula, formula . It is a white powder which is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, Zinc metabolism, food supplements, rubbe ...

(ZnO intermediate reflector: ZIR) or

silicon oxide Silicon oxide may refer to either of the following: *Silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the maj ...

(SiOx intermediate reflector: SOIR) between the top and the bottom cell. Due to its lower refractive index of around 2 comparing to the surrounding silicon (4) light is reflected back into the top cell. This increases the top cell current from around 10mA/cm to 12mA/cm, but reduces the bottom cell current by an equal amount.

The word micromorph

This artificial word was first mentioned in a scientific publication of the

University of Neuchâtel The University of Neuchâtel (UniNE) is a French-speaking public research university in Neuchâtel, Switzerland. The university has four faculties (schools) and more than a dozen institutes, including arts and human sciences, natural sciences, ...

research group of Prof.

Arvind Shah Professor Arvind M. Shah (1939-2020) retired from his professorship in the Department of Sociology at the University of Delhi in 1996. He had been a student of M. N. Srinivas in 1952 and became a teacher in sociology at Maharaja Sayajirao Univer ...

by the author J. Meier in the year 1995, but is based on long pioneering research of several authors and of several years. For a detailed list of publications, see the two main research group's publications website under http://pvlab.epfl.ch and under https://web.archive.org/web/20110222142422/http://www.fz-juelich.de/ief/ief-5/publicger/ Years later, other European, Japanese and American research groups started research activities in the field of improving the conversion efficiency of thin-film silicon solar cells by utilizing the

stacked solar cell ''Stacked'' is an American television sitcom that aired on Fox from April 13, 2005, to January 11, 2006. Premise ''Stacked'' was described as the opposite of ''Cheers'', instead of a smart person in a "dumb" place, it is based on the concept of ...

concept, naming the micromorph device 'hybrid' solar cell or naming the

microcrystalline A microcrystalline material is a crystallized substance or rock that contains small crystals visible only through microscopic examination. There is little agreement on the range of crystal sizes that should be regarded as microcrystalline, but ...

silicon absorber 'nanocrystalline' or even 'policrystalline' silicon. The word 'micromorph' has been lately claimed to belong to an equipment manufacturer of silicon coating tools, but in a patent judgement, this claim has not been accepted by European

patent office A patent office is a governmental or intergovernmental organization which controls the issue of patents. In other words, "patent offices are government bodies that may grant a patent or reject the patent application based on whether the applicati ...

s.O. Papathanasiou, "A good day for Ms. Schönefeld-Schnuck PI 5/2009 page 44", http://www.op-solar.de/pdfs/A%20good%20day%20for%20Schoenefeld-Schnuck.pdf

External links

* Presentation with informative pictures and current state of industrial production: http://www.swisslaser.net/libraries.files/UlrichKrollOerlikon.pdf

References

{{reflist Solar cells

The micromorph cell

The intermediate reflector

The word micromorph

See also

External links

References