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A conjugated system is formed where carbon atoms covalently bond with alternating single and double bonds.These hydrocarbons' electrons pz orbitals delocalize and form a delocalized bonding π orbital with a π* antibonding orbital.It is argued instead that dispersive transport arises from the loss of carriers to trap states.
The energy separation between the HOMO and LUMO energy levels is considered the band gap of organic electronic materials and is typically in the range of 1–4 e V.
All light with energy greater than the band gap of the material can be absorbed, though there is a trade-off to reducing the band gap as photons absorbed with energies higher than the band gap will thermally give off its excess energy, resulting in lower voltages and power conversion efficiencies.
In organic photovoltaics, effective fields break up excitons by causing the electron to fall from the conduction band of the absorber to the conduction band of the acceptor molecule.
It is necessary that the acceptor material has a conduction band edge that is lower than that of the absorber material.
This work presents new insights into the measurement of charge transport, the underlying physics, as well as new approaches for modelling.
Numeric simulation software using a drift-diffusion-recombination model is developed and applied to organic photovoltaic devices.
The process of charge transport is fundamental to the operation of all electronic devices.
In organic photovoltaics, high efficiencies can only be achieved if charge transport is able to extract charge carriers from the active layer with minimal recombination losses.
Depending on the band gap of the light-absorbing material, photovoltaic cells can also convert low-energy, infrared (IR) or high-energy, ultraviolet (UV) photons into DC electricity.
A common characteristic of both the small molecules and polymers (Fig 1) used as the light-absorbing material in photovoltaics is that they all have large conjugated systems.