Wafer-based crystalline silicon

Wafer-based crystalline silicon has been the dominant technology since the birth of photovoltaics. It is abundant, reliable and scientifically well understood, as it has enjoyed the knowledge and technology originally developed for the microelectronics... 

Although ZnO has also been applied in so-called amorphous/crystalline heterojunction solar cells consisting of a (doped) silicon wafer and thin doped a-Si H layers to build the p-n junction, we will restrict ourselves here to solar cells and modules with amorphous and/or microcrystalline absorber layers, i.e., real thin film silicon solar cells. For detailed information on the use of ZnO in crystalline silicon wafer based devices, the reader is referred to the literature (see e.g. [23,24]). 

In addition to the cost effectiveness of silicon ribbons, energy payback time (i.e. the time needed to produce the amount of energy that was consumed during the manufacturing of a solar system) is drastically reduced. In a recent life-cycle analysis of crystalline silicon wafer based PV systems, it was demonstrated that the energy pay-back times can be reduced by half (based on cut multi-crystalline wafers), by the use of RGS ribbons for systems in central Europe [97]. 

Current tendencies for multi-crystalline wafer based solar cells are heading towards thinner and larger wafers. Ribbon silicon based wafer technologies have to deal with these developments in the future to maintain their cost effectiveness. As thin EFG and RGS wafers have already been produced on a laboratory scale with thicknesses of <200 fim, their industrial application remains a topic for ongoing research. 

In essence, a DSSC device is composed of a transparent photoactive anode and a photo-inert counter electrode (cathode) sandwiching an electrolyte-containing redox mediator (Figure 6.1(a)). Conceptually, the device is based on the superposition of active layers whose thicknesses are 10- to 20-fold less than that of crystalline silicon wafers. Moreover, the requested purity of materials is 10-100 times less than for a silicon device. 

Solar voltaic cells based on crystalline silicon have operated with a 30% efficiency for experimental cells and 15-20% for commercial units available in 2008, at a cost of around 15 cents/kWh, compared to 4-7 cents/kWh for fossil fuel-fired power plants and 6-9 cents for those fired by biomass. Costs of photovoltaic electricity have shown a continuous downward trend. Part of the high cost in the past has resulted from the fact that the silicon used in the cells must be cut as small wafers from silicon crystals for mounting on the cell surfaces. Significant advances in costs and technology are being made with thin-fllm photovoltaics, which use an amorphous silicon alloy. These cells are only about half as efficient as those made with crystalline silicon, but cost only about 25% as much. A newer approach to the design and construction of amorphous silicon film photovoltaic devices... 

The possibility of surface functionalization of the hydroxylated surface of silicon based materials with phosphazene substrates has been explored by a combination of experimental XPS analysis and theoretical ab initio calculations it has been shown that, in the interaction of [N3P3CI6] with the Si(100)-OFI surface, water plays a crucial role and a solvent such as THF is essential. " Also, the specific surface modifications of silicon-based materials such as silica gel beads and crystalline Si(lOO) wafers, have been achieved by reacting the residual with the pendant NHCFl2CH2CH2Si(OMe)3 groups of cyclotriphosphazenes carrying an equimole-cular proportion -OCeH4-/ -CN substituents used as markers through its IR band at 2230 cm. ... 

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