Harald Hoppea and Niyazi Serdar Sariciftci, J. Mater. Res., Vol. 19, No. 7, Jul 2004
(Excellent Review with an extensive reference list)
- Organic polymers are currently made by wet solution processing or dry thermal evaporation of the organic constituents.
- The potential of semiconducting organic materials to transport electric current and to absorb light in the ultraviolet (UV)-visible part of the solar spectrum is due to the sp2-hybridization of carbon atoms.
- Most of the organic semiconductors are hole conductors and have an optical band gap around 2 eV.
- 2 main challanges for organic solar cell technology: conversion efficiency and lifetime & stability
- Conversion of light into electric current in 4 Steps: (i) Absorption of a photon leading to the formation of an excited state, the electron-hole pair (exciton). (ii) Exciton diffusion to a region, where (iii) the charge separation occurs. (iv) Finally the charge transport to the anode (holes) and cathode (electrons), to supply a direct current for the consumer load.
- Mechanism of charge transport: To reach the electrodes, the charge carriers need a net driving force, which generally results from a gradient in the electrochemical potentials of electrons and holes. Two “forces” contribute to this: internal electric fields and concentration gradients of the respective charge carrier species. The first leads to a field induced drift and the other to a diffusion current. Thin film devices (<100>
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