Organic Semiconductors
What are semiconductors?
Semiconductors are partially conductive materials. There are two types of semiconductors, extrinsic and intrinsic, intrinsic semiconductors being those materials that need to be heated to allow electron mobility and extrinsic semiconductors being those that are doped with different elements to produce either an N - type or P-type semiconductor. Doping involves the introduction of impurities to a material. N-type semiconductors are those doped with pentavalent elements such as phosphorous and arsenic, n-type semiconductors are those with an extra electron in its’ conduction band. P-type semiconductors are those doped with trivalent elements such as gallium and aluminum, p-type semiconductors have one less electron in its conduction band, this lack of an electron is referred to an electron hole. (Britannica ,2022) The ease of conduction in a semiconductor is based on the distance between the valence band and the conduction band which is referred to as the band gap. Smaller band gaps use less energy in order for an electron to move from the valence band to the conduction band when a voltage is applied, the valence band being the highest occupied molecular orbital and the conduction band the lowest unoccupied molecular orbital .
What are organic Semiconductors?
Organic Semiconductors are semiconductors made of materials comprised of pi (π)conjugated bonds. Pi bonds are the lateral overlap of two pairs of atomic orbitals, each belonging to a different atom. Examples: Melanin, Chlorophyll, Polyvinyl Alcohol
How are organic Semiconductors made?
Organic semiconductors are efficiently made by solution processing techniques such as inkjet printing, doctor blading and slot-die coating. Each process involves the organic semiconductor in a precursor solution which is ejected onto a substrate except in the case of doctor blading, where the precursor solution is spread across the substrate using a blade to achieve uniformity. These solution processing techniques are scalable at a low cost in comparison to methods used for the inorganic semiconductors, these include physical vapor deposition, molecular beam epitaxy and pulsed vapor deposition.
Applications of Organic Semiconductors
Some applications of organic semiconductors include Organic Thin film Transistors (OTFT), Organic photovoltaics (OPV) and Organic Light Emitting Diodes. (OLED)
Challenges
Organic semiconductors (OSC) have yet to match the parameters of inorganic semiconductors. Parameters such as electron mobility (cm2 V-1 s-1), Power conversion efficiency and oxidative stability. However, with recent advances in organic semiconductor technology, a stretchable polymer transistor array achieved a charge carrier mobility similar to that of amorphous silicon. Therefore with further research, OSCs could achieve parameters similar to that of Inorganic semiconductors (Wang et al , 2018).
References: “Semiconductor.” Encyclopedia Britannica. Encyclopedia Britannica, Inc. Accessed January 17, 2023 . https://www.britannica.com/science/semiconductor.
Wang, Sihong, Jie Xu, Weichen Wang, Ging-Ji Nathan Wang, Reza Rastak, Francisco Molina-Lopez, Jong Won Chung, et al. “Skin Electronics from Scalable Fabrication of an Intrinsically Stretchable Transistor Array.” Nature News. Nature Publishing Group, February 19, 2018. https://www.nature.com/articles/nature25494
By Narayan Shiva Sankar
Bsc Physics