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Title: Understanding defect distributions in polythiophenes via comparison of regioregular and regiorandom species

Organic photovoltaics (OPVs) are regarded as promising for solar-electric conversion with steadily improving power conversion efficiencies. For further progress, it is crucial to understand and mitigate defect states (traps) residing in the band-gap of OPV materials. In this work, using capacitance measurements, we analyzed two major bands in the density of states (DOS) energy spectra of defects in poly(3-hexylthiophene) (P3HT); regio-regular and regio-random species of P3HT were compared to elucidate the role of morphological disorder. To accurately interpret the obtained DOS profile, trap emission prefactors and activation energy were extracted from temperature dependent capacitance-frequency measurements, while doping, Fermi energy, built-in voltage, and energy levels of the defects were extracted from capacitance-voltage measurements. We identified that the lower energy band—misinterpreted in literature as a defect distribution—stems from free carrier response. The higher energy defect distribution band for regio-random P3HT was an order of magnitude higher than region-regular P3HT, thus stemming from morphological disorder. Impedance spectroscopy was also employed for further comparison of the two P3HT species.
Authors:
 [1] ;  [1] ;  [2]
  1. Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa 50011 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
22492984
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 20; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 14 SOLAR ENERGY; ACTIVATION ENERGY; CAPACITANCE; CARRIERS; COMPARATIVE EVALUATIONS; DEFECTS; DENSITY OF STATES; ELECTRIC POTENTIAL; ENERGY CONVERSION; ENERGY EFFICIENCY; ENERGY SPECTRA; FERMI LEVEL; FREQUENCY MEASUREMENT; ORGANIC MATTER; PHOTOVOLTAIC EFFECT; SPECTROSCOPY; TEMPERATURE DEPENDENCE