Holes are injected into the HOMO from an anode, and electrons are injected into the LUMO from a cathode. The carriers hop through the organic layers under an applied electric field, meet, form excitons, and radiatively decay to emit light.
Organic semiconductors have revolutionized the field of electronics by bridging the gap between plastic materials and traditional solid-state physics. Unlike silicon or gallium arsenide, which rely on rigid covalent crystal lattices, organic semiconductors are carbon-based molecules or polymers bound by weak intermolecular forces. This structural difference introduces unique physical phenomena, such as localized electronic states, strong electron-phonon coupling, and excitonic solar conversions.
When an OSC absorbs a photon, it creates an exciton—a bound electron-hole pair. In inorganic semiconductors, the high dielectric constant ($\varepsilon_r$) screens the Coulomb attraction, resulting in Wannier-Mott excitons with large radii and low binding energy ($\sim$ meV), which dissociate easily at room temperature. physics of organic semiconductors pdf
OFETs act as the fundamental switches for flexible circuitry. An external voltage applied to a modulates the charge density at the interface of an organic semiconductor and an insulator (dielectric). This accumulation layer permits a controlled current to flow between the Source and Drain electrodes. Organic Photovoltaics (OPVs)
Analogous to the top of the valence band in inorganic crystals. It represents the highest energy level occupied by electrons in the ground state. Holes are injected into the HOMO from an
Because electrons and holes are localized on individual molecules or polymer segments, transport occurs through —a phonon-assisted, quantum-mechanical tunneling process between adjacent sites. The hopping rate ( νijnu sub i j end-sub ) between site is commonly modeled using the Miller-Abrahams formalism :
: Solar cells made from organic polymers that can be printed or coated onto large, flexible surfaces. 4. Comparison to Inorganic Semiconductors Inorganic (e.g., Silicon) Organic (e.g., Pentacene) Material Base Crystalline lattice Carbon-based molecules Flexibility Brittle/Rigid Flexible/Stretchable Processing High-temp vacuum Low-temp solution processing Transport Hopping/Polaronic 5. Recommended Resources for PDF Guides Unlike silicon or gallium arsenide, which rely on
Unlike highly crystalline silicon, most organic semiconductor films are amorphous or polycrystalline. This structural disorder creates variations in molecular orientation and packing, leading to a Gaussian or exponential distribution of localized electronic states. Charge transport does not occur through continuous energy bands but rather via movement through this disordered energy landscape. Hopping Transport Mechanism
The energy difference between the HOMO and LUMO defines the fundamental electronic bandgap ( Egcap E sub g