Photovoltaic Cells Vs Photosynthesis Process

Do they have anything in common? Cross the road and ask the first person you meet the following question: "according to your knowledge is there any correlation between a photovoltaic cell and the photosynthesis process?" At 99,9 % the answer is no, there is not any correlation (better not to say at 100%, you never know).
Probably the answer is negative because the person does not remember or does not know what a photovoltaic cell is and what the photosynthesis process is. Let's remember together, briefly, what they are.
The photovoltaic cell is the base element constituting a photovoltaic module, which is able to convert straightly the solar energy in electric energy through the photovoltaic effect. The photosynthesis is an endothermic process that happens in the plants and in some unicellular organism and thanks to it the solar energy is transformed in chemical energy, included in glucose molecules and in the link of other organic substances.
Now we have found the connection between the photovoltaic cell and the photosynthesis process: both convert the solar energy, the first one in electric energy the second one in chemical energy. Due to the above mentioned connection Michael Gratzel, professor of chemistry physics at Losanna university, in 1991 showed the photovoltaic cell based on the process inspired to the plants photosynthesis. The cell Gratzel, in its functioning, refers to the plants photosynthesis:

• It uses an organic colorant equivalent to the chlorophyll to absorb the light and to produce an electron flow;
• It uses multiple layers to improve the efficiency both the light absorbing and the electrons collecting.

The base element of these cells is the Titanium dioxide (TiO2), a material that is largely used (for ex. in the paints production or of ceramic materials) and has a low cost. It is generally produced in the shape of nanoparticles that are particles with dimensions of about one millionth of millimetre. This material is able to absorb only ultraviolet radiations, but linking them to the nanoparticles surface through suitable molecules of colorants, named activators or sensitizers, it is possible to absorb the visible radiation too. Therefore the layer presence of TiO2 is necessary to increase, hugely, the efficiency of the light collecting, spreading the colorant over a large area in equivalent manner as it happens for the chlorophyll in the chloroplasts. Since the colorant layer is very thin, almost all the electrons, produced from the light absorbing, are collected from TiO2. Initially, molecules of colorant belonging to the same family of the bilberry pigments were used , now other compounds that allow to absorb even more the visible components of the solar radiation are used. By these activated nanoparticles, porous layers are realized, with thickness lower than a thousandth of millimetre, and these layers are impregnated with electrolytes. Once this layer has been placed between two suitable supports, in advance a thin metallic deposition on them has been done, the device is ready. The process of light absorbing produces a cumulation of charges on the electrodes and, in this way, it creates a voltage between the two metallic layers, as between the two accumulator poles. The current efficiency of this cell is of 10 % approximately, so it is at the same level of the silicon amorphous cells, but the production costs are significantly lower. Moreover, compared to the silicon amorphous cell, it has the advantage that it can be produced on large dimension surfaces and on flexible supports that can be integrated in the buildings structure easily.
Below we can see the Gratzel cell:

• A - up there is the counter electrode (conductor glass), down the TiO2 glass plate with colour stain;
• B - the assembled cell;
• C - the final assembling: cell with clips.