In addition to functioning as a solar cell for directly utilized and generated electrical energy, DSSC can also be used as a breaker of water in the process of hydrogen production. Electrical energy produced by solar cells can not be stored directly in the form of electricity, but it can be stored in another form, one of them in the form of chemical energy such as hydrogen. Hydrogen is one element used as fuel, because it has highest energy content per unit the among the various types of fuel (Bard et al, 1995). The use of hydrogen is quite rapid development of vehicles, portable electronic equipment, to household tools.
In a simple solar cell consists of the junction of semiconductor material of p- and n-type (p-n junction semiconductor). if the sunlight expose it, there will be a flow of electrons and consequently electron flow is called electricity. The main part of the energy changes of sunlight into electricity is the absorber. Sunlight is composed of various types of electromagnetic waves, the absorber is expected to absorb as much possible radiation coming from the sun. To obtain high efficiency solar cell, the photons from sunlight must be absorbed as much as possible, reducing light reflection and recombination and increasing the conductivity of materials.
Hydrogen Production from Water Splitting
Hydrogen can be produced by using a simple combination of two different systems namely photovoltaic system which it generates electricity and water electrolysis system. Each solar cell can generate higher voltages from 1.5 V elektorlisis water used to directly produce hydrogen and oxygen (Dimroth et al, 2006).
Figure 3. Single system of photovoltaic and electrolysis of water
Figure 4. Conceptual design of hydrogen-producing reactor
the DSSC as power plants
Figure 5. A simple schematic of a tandem solar cell systems and fuel cells
Electrolysis of water in the electrolyte can theoretically take place on the voltage 1.23 V, but in practice the new reactions can take place at voltages above 1.48 V. This is because many external factors affecting the system must be passed as more and potential obstacles. The thermodynamic enthalpy of water electrolysis reaction of 285.83 kJ / mol (25 º C, 1 atm). That amount includes Gibbs' free energy of ΔG = 237.1 kJ / mol and the heat energy TΔS = 48.7 kJ / mol, which it contributed an increase of entropy in the process of dissociation energy not used for work (workless energy). If it is assumed that all the energy needed for electrolysis of water comes from electricity, the termoneutral potential at 1.48 V (39kWh/kg) must be supplied for each atom H. When used current is very small, then there must energy supply TΔS heat from the environment (Dimroth et al, 2006).
Combined DSSC System, Air-breaking system and fuel cell
The hydrogen produced can be used as fuel for vehicles and portable devices using fuel cell systems. During this process of hydrogen production requires substantial energy and also produce waste which it can pollute the environment. The use of tandem devices (devices combined) ie solar photovoltaic systems and water electrolysis system to produce hydrogen offers many advantages such as environmentally friendly energy and it does not require a large fee for its production (Dimroth et al, 2006). In simple tandem devices can be illustrated in Figure 4.
Use of DSSC as sunlight harvesters have given a conversion efficiency of more than 10%. The system combined by device can be an alternative production of hydrogen as an environmentally friendly fuel, by utilizing the DSSC as a power plant used for electrolysis of water, to be the solution to overcome the problem of energy scarcity while maintaining the quality of the environment, so that life is on better and safe earth.
Hydrogen generated from this system can be directly applied to the fuel cell as a tandem system. Vehicles using a tandem solar cell systems and fuel cells provide the possibility for more comfortable and secure in use, in other words vehicle tandem system of fuel cell and solar cell open up opportunities to use water as fuel. This can exactly reduce the cost of hydrogen fuel production at refineries, because hydrogen will be produced directly on the vehicle and it is immediately directly used as an energy source, so that accidents can be avoided due to hydrogen burning. Figure 5 presents a simple scheme of a tandem system of fuel cell and solar cell.