The optical spectrum dynamic variable, dI/dλ positive value (from UV to green) and negative value of dI/dλ (from green to red ) are actually defined what in terms of energy transfer and its interaction?
Dear Bablu,
welcome,
The interaction of a semiconductor with optical radiation of different wave length depends on the energy band structure of this semiconductor material. The energy band structure gives the electron energy as a function of its momentum in the conduction band and valence band.
So any material with a limited thickness behaves as a band stop filter, where it absorbs the incident radiation in a certain wavelength range.
The highest cut off wavelength is determined by energy gap of the material and its thickness. While the cut off at the shortest wavelength is because of surface effect where the absorbed energetic photons will reside in a dead region where the recombination of the photogenerated electron hole pairs will instantly recombine and therefore can not be detected.
The presence of the grains affect appreciably the energy band structure and therefore can vary the filter characteristics of material.
This is a conceptual answer on you question.
Best wishes
@ Prof. Abdelhalim Zekry The coulomb capture radius, rc is related to electrical permittivity. The molecular kinetic energy is associated to the thermal diffusion energy, KβT [Quantum-mech]. In the absence of optical excitation, thermal and kinetic energy are the same. Under irradiance, the kinetic energy is prominent. At certain settings, the thermal energy is equal to the coulomb’s potential energy, the coulomb capture radius, rc is defined as the Onsager radius, Ro [therml diffu leng relt].
The variation of rc with Ro is a factor of DP and the change of thermalization effect. The DP is a factor of exciton binding energy, Eb and thermalization changes thermal diffusion energy, KβT. The variation of kinetic energy for photo excitation may influence on charge delocalization. Currently it is revealed that the thermal effect on carrier delocalization or transport properties is some extend relevant to the materials quality or architecture. The thermalization related thermal diffusion length has the key influence on charge dissociation or dislocation. The diffusion constant in any materials is linked to the mobility.
Carrier mobility, μ and thermal diffusion energy, KᵦT could vary the thermalization length, l at variable temperature with thermal relaxation constant, τ.
In this approach, the molecule volume related rc counter balance with thermalization energy linked, l is the thermodynamic tricky that may usually occur in OPV.
So, the carrier generation, separation and its effective radiative recombination for photocurrent generation process whether are linked to l, rc and KβT or Eb inter-relationship or not?
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