Thin film - Amorphous (a-Si)

"Thin-film technology is simultaneously one of the oldest arts and one of the newest sciences"

Solar photovoltaic technology is a promising alternative energy source to meet the world energy demand because it harvests energy from the sun. 174 petawatts of incoming solar radiation reaches to the earth at the upper atmosphere at any given time.

Solar energy is used synonymously with solar power and sometimes more specifically to refer to the transformation of sunlight into electricity. This can be done via photovoltaic effect or by heating a transmission of fluid to produce vapor to run a generator. Solar cell device is used to convert sunlight into electricity. Basically, solar cell depends on photon absorbtion and the following generation of electron-hole pairs in the semiconductor material. A solar cell is fundamentally a p-n junction diode. When semiconductors absorb light that has energy greater than bandgap energy, electron-hole pairs are created, the created carriers are separated by the internal electric field at the p-n junction and are collected by the contacts.

The first generation of solar cells are silicon wafer-based solar cells. Finally it would be replaced by a second generation of lower cost thin-film based solar cell technology involving a different semiconductor. CdS, a:Si (amorphous silicon), CdTe, CuIn1-xGexSe2 and thin-film poly:Si (polycrystalline silicon) have been regarded as thin-film solar cell candidates.

Thin film cells are deposited directly onto glass, stainless steel or plastic substrates. Conversion efficiencies for commercial photovoltaic modules range from 8% to 15 % depending on type of material and fabrication method.

Photovoltaics may be regarded as space-age technology, but it is a technology that in fact has been around for quite some time. The photovoltaic effect was first reported by French physicist Edmond Bacquerel in 1839[4]. In one of electrical workout, he placed two plates in a conductive fluid, and when he exposed the setup to the sunlight incidentally he observed a small voltage. Nearly 40 years later, in 1873 English physicist Willoughby Smith discovered that selenium was sensitive to light[5]. Light struck selenium and electrical current is generated. The first working solar cell was constructed by Charles Fritts in 1886. These prototype cells were made of selenium and achieved efficiencies around 1 %. In an early publication Fritts expressed that one of the great advantage of solar cell is that "the supply of solar energy is both without limit and without cost, and will continue to stream down on earth after we exhaust our supplies of fossil fuels"