Organic Photovoltaic Cells

Nowadays, uncertainty about the energy future is growing more and more. The energy sources that contribute most today are limited in nature and it is vital to find renewable resources. Renewable energies are those that are produced continuously and are inexhaustible on a human scale. One of the best known renewable energies is solar energy.

Types of Organic Photovoltaic Cells

Organic photovoltaic cells appeared in 1990 with the intention of reducing the cost of photovoltaic electricity. The low cost of organic semiconductors, among them polymers, small molecules of materials deposited by thermal evaporation, make them a much more accessible, cheap and environmentally friendly alternative. There are four main types of organic photovoltaic cells:

  • Grätzel Cells: These cells use an adducts or pigments that absorb much light and quickly transfer the electron to a nanostructured oxide such as TiO2. To make this process reversible and continue to absorb light, the gap remaining in the pigment must be extracted. This task is performed by a redox agent or liquid electrolyte.
  • Multilayer Cells. Successive layers of different semiconductor materials are sequentially deposited with the purpose of maximizing the intensity of the optical field in the areas where the loads are photographed; Thus optimizing both the absorption and the dissociation of the excitons.
  • Cells with multiple internal organic heterounions: Two polymer immiscible materials with different electron affinities and ionization potentials are mixed in the same solution. From this, by evaporation of the solvent, a thin film is formed with domains of both materials at nanoscale to optimize both the exciton dissociation process and the charge transport to the electrodes.
  • Organo-inorganic Hybrid Cells: These cells function in a manner very similar to those described in the previous section. The role of accepting electrons and transporting them to their respective electrodes corresponds, in this case, to inorganic materials with a large band gap such as TiO2 or ZnO. Nanostructured these materials in the form of nanopores or nanowires on the substrate is crucial to ensure effective transport of cargo. Subsequently the polymer is deposited from the dissolution on this nanostructure.

As with traditional photovoltaic cells, all organic photovoltaic processes are designed with the use of dopants that increase the standard performance of the original process. On the one hand, certain polymers improve their reactive properties by working in the presence of a redox solution. Others, however, need a ‘work’ electrode, which facilitates the movement of electrons from the electrochemical solution forming the cell.

Traditional Photovoltaic Cell and Organic Photovoltaic Cell

Organic photovoltaic cells have the same conductive properties as silicon but can be printed or adhered on almost any type of material.
The main difference between conventional semiconductors and conjugated polymers is that in the former the excited electron and the resulting gap migrate freely towards opposite electrodes while in the seconds the electron and the gap that are generated after a photon is structurally bound Of excitation.

By creating interfaces between conducting polymers with different electron affinity, it is possible to transfer electrons between polymers. This process, known as photoinduced electron transfer, is able to separate the charges, and the bond created at the donor-acceptor interface is analogous to conventional semiconductor heterounions.

The useful life is measured in cycles, which are defined as the number of times the charge and discharge occurs. With each cycle, the battery is losing properties, and aging decreasing the maximum capacity it can reach. The higher the discharge (decrease in capacity) the lower the number of cycles and, consequently, the shorter the useful life. The service life of the panels, as well as their efficiency, depends mainly on the process and the quality and the interaction in the multilayer device of the system components.

Yet there is some optimism in solving these problems of organic cells. The biggest challenge in developing such high performance is to optimize the absorption of electrically conductive materials.

Advantages of Organic Photovoltaic Cells

Organic photovoltaic cells have in their favor that they can be adhered as an ultra thin layer of two semiconductor polymers on any plastic surface. In addition solar panels composed of organic cells are cheaper, less heavy and easier to install.

Organic solar cells have had to meet a number of requirements in terms of stability, efficiency and cost in order to be able to compete with existing silicon technology and to find new applications. Organic materials have advantages from the point of view of manufacturing costs, the possible impact on environmental safety and fundamentally the possibility of producing flexible devices; Which absorb radiation at different wavelengths and in which it is possible to modulate the electronic properties making use of the resources provided by organic synthesis.

These properties represent a significant advance in the design of electronic devices. And it is in this sense where we direct our research in relation to the Organic Photovoltaic Cells. Our efforts are focused on creating devices that use as a basis their structure Organic Photovoltaic Cells. To do this, we investigate which are the molecular structures most suitable to achieve the best results.

Photovoltaic devices based solely on organic materials have in recent years attracted great interest as a result of their lightness, low cost of manufacture and the possibility of making thin films of these materials on relatively large surfaces.

Although, on the other hand, the low values ​​found for the conversion efficiency in these photovoltaic devices are due to the low photogeneration efficiency of charge carriers, as well as the high electrical resistivity of the organic materials derived from low mobility and low density of cargo carriers. It is for this reason that we continue to investigate the most appropriate way of solving these problems.

Prof. Andrew Watt