Organic Solar Cell (OPV) Materials For Solar Energy

Organic solar cell (OPV) is a solar cell whose absorber layer is an organic semiconductor (polymer or small molecule). The preparation of organic semiconductor materials requires the use of highly conjugated organic materials. The conjugation of organic molecules results in the delocalization of the electrons associated with the double bond over the entire conjugation length. These electrons have higher energy than other electrons in the molecule, and can impart conductive or semi-conductive properties to organic materials. The working process of OPV includes four aspects: light absorption, exciton diffusion, exciton dissociation, and charge transport and collection. When the energy of the incident light is greater than the energy gap, the donor molecules are excited and the electrons transition from the HOMO orbital to the LUMO orbital, thereby forming a hole in the HOMO orbital. When holes and electrons bind to each other to form electron-hole pairs, excitons are formed. The excitons are diffused and dissociated to obtain free electric charges, and the photocurrent is collected in the active layer to complete the photoelectric conversion. The specific advantages of OPV are as follows: (1) Great chemical variability and a wide range of sources of raw materials; (2) It can change and improve the material's spectral absorption capacity, expand the spectral absorption range, and improve the carrier's transport capacity through a variety of ways; ( 3) It is easy to process and can be processed in a large area; (4) It is easy to carry out physical modification; (5) The battery production can be diversified; (6) The cost is low. OPV has the advantages of low manufacturing cost, wide material sources, simple preparation process, light weight, flexibility, ultra-thin, transparent and other advantages. It is convenient for transportation and flexible deployment, and is of great significance for large-scale use of solar energy to provide cheap electricity. The flexibility and light weight of organic solar cells have greatly broadened the application range and environmental compatibility of solar cells, and the installation and use of solar cells can be gradually expanded from fixed plane installation to more flexible curved installation mode, which is conducive to the realization of portable applications and is widely used in building integration and other fields.

OPV working mechanismFigure 1. OPV working mechanism

Applications:

  • Electrode materials: In the organic redox flow battery, the electrode itself is inert and does not participate in the redox process, and the energy storage only depends on the redox reaction of the active substance itself on the electrode surface. Electrode is the site of redox reaction of active substances in the battery. The characteristics of electrode material have a direct impact on electrochemical reaction. Therefore, the electrode of organic redox flow battery should have high conductivity, which can effectively reduce the influence of ohmic polarization. Furthermore, the electrode material should have high activity in response to specific active substances, and the active substances in the flow state can react on the electrode. Electrode materials should be chemically stable in common highly corrosive environments. In addition, given the cost of batteries and the feasibility of applications, the materials used to make electrodes should be cheap, readily available and have a long life.
  • Electrolyte active material: Electrolyte solution with active material is the storage medium of organic redox flow battery, which has significant influence on the performance of the battery. The redox reversibility of the electrolyte active material determines the charge and discharge efficiency of the battery. The solubility of electrolyte active materials in the supporting electrolyte determines whether the battery can have large capacity and high energy density. The redox potential of positive and negative active materials determines the voltage window range of the battery.
  • Diaphragm material: Diaphragm plays an important role in the whole battery operation process, and the performance data of the organic redox flow battery are closely related to diaphragm. The diaphragm material completely separates the redox active electrical pair to prevent short circuits. The selectivity of the diaphragm is critical because cross-contamination of the positive and negative electrodes leads to a loss of efficiency. Furthermore, organic redox flow battery need to be assembled and sealed either by a single cell or a stack. Stress is generated during this process, so the diaphragm material is required to have good mechanical properties.

Reference

  1. Christie L. Cutting,Monojit Bag,D. Venkataraman. Indoor light recycling: a new home for organic photovoltaics [J]. J. Mater. Chem. C, 2016, 4, 10367-10370.
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