Scholarly Publications - Chemistry

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Fermi level pinning ınduced by doping in air stable n type organic semiconductor
(American Chemical Society, 2020) Sharma, S.; Ghosh, S.; Ahmed, T.; Ray, S.; Islam, S.; Salzner, Ulrike; Ghosh, A.; Seki, S.; Patil, S.
Doping of organic semiconductors enhances the performance of optoelectronic devices. Although p-type doping is well studied and successfully deployed in optoelectronic devices, air stable ntype doping was still elusive. We succeeded with n-type doping of organic semiconductors using molecular dopant N-DMBI under ambient conditions. Strikingly, n-type doping accounts for a gigantic increase of the photoconductivity of doped thin films. Electrical and optical properties of the n-doped molecular semiconductor were investigated by temperature dependent conductivity, electron paramagnetic resonance (EPR), and flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements. A significant reduction and saturation in activation energy with increasing doping level clearly suggests the formation of an impurity band and enhancement in carrier density. Computational studies reveal the formation of a charge transfer complex mediated by hydrogen abstraction as the rate-determining step for the doping mechanism. The colossal enhancement of photoconductivity induced by n-doping is a significant step toward optoelectronic devices made of molecular semiconductors.