Features And Benefits
DSSC Explained
In silicon solar cells, the semiconductor (Si) is in charge of both the creation and the transport of the free electrons. This is not the case in DSSCs: a semi-conductor is still used, but only for the diffusion of electrons to the electrode. The electron itself comes from the photoexcitation of a dye.
The basic composition of a cell, as imagined by Professor Michael Grätzel is as follows:
A transparent conducting oxide (TCO) is deposited on a transparent substrate, glass or plastic, to make two electrodes.
On the working electrode, a thin layer (around 10 µm) of nanoparticles of a semiconductor, the titanium dioxide (TiO2), is deposited. Then, the TiO2 is sintered to create “necks” between the nanoparticles of TiO2, and allow the transport of the electrons from particle to particle to the TCO.
The electrode with the TiO2 is soaked in a dye, composed of either ruthenium or organic dyes. The molecules of dye will cover the surface of every nanoparticle. The dye is the photoactive material of the cell: it will catch the photons of the incoming light and convert them into electrons. The diffusion of those electrons through the TiO2 and the TCO creates a current. This electricity is then used to power external devices or to charge batteries.
At this stage, the dye has given an electron to the external circuit and therefore is missing it, it is “oxidised”. To be able to absorb another photon and created another free electron, it should first be “reduced”, which means that it should get a new electron. This electron is coming back from the external circuit through the counter electrode. The electrolyte, is used to transport the electrons from the counter electrode to the dye between the nanoparticles of TiO2. The cycle is now complete and will begin again with the next absorption of a photon by the dye.