Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Electrical and optical properties of poly͑3-hexylthiophene-2.5diyl͒ ͑P3HT͒ used as the main component in a polymer/fullerene solar cell were studied. From the study of space-charge limited current behavior of indium-tin-oxide ͑ITO͒/P3HT/Au hole-only devices, the hole mobility and density were estimated to range from 1.4ϫ10 Ϫ6 cm 2 /V s and 5.3ϫ10 14 cm Ϫ3 at 150 K to 8.5 ϫ10 Ϫ5 cm 2 /V s and 1.1ϫ10 15 cm Ϫ3 at 250 K, respectively. The highest occupied to lowest occupied molecular orbital energetic difference was estimated from absorption spectrometry to be about 2.14 eV. Strong quenching of photoluminescence when the polymer was mixed with ͓6,6͔-phenyl-C 61 butyric acid methyl ester ͑PCBM͒, provided evidence of photoinduced charge transfer from P3HT to PCBM. Characterization of ITO/PEDOT:PSS/P3HT:PCBM/Al solar cells was done by analyzing the dependence of current density-voltage characteristics on temperature and illumination intensity. The main solar cell characteristics recorded at 300 K under 100 mW/cm 2 white-light intensity were: Open-circuit voltage 0.48 V, current density 1.28 mA/cm 2 , with an efficiency of 0.2%, and fill factor of 30.6%. Open-circuit voltage decreased almost linearly with increasing temperature, while short circuit current density increased with temperature, saturating at around 320 K, and decreased thereafter. Power conversion efficiency and fill factor were maximum around 3 mW/cm 2 due to the poor bulk transport properties of the active layer.
We studied the temperature dependent current-voltage characteristics of regioregular poly (3-hexylthiophene 2.5-diyl) (P3HT) thin films sandwiched between indium tin oxide (ITO) and aluminum (Al) electrodes (ITO/P3HT/Al devices), with the aim of determining the current limiting mechanism(s) in these devices, and the temperature and/or applied electric field range(s) in which these mechanisms are valid. The current-voltage characteristics of the ITO/P3HT/Al devices showed that current flow across the device is limited by hole injection at the Al/P3HT interfaces at temperatures below 240 K, when the device is biased with high potential on Al. Above this temperature, the bulk transport properties control the characteristics. For the reverse bias, the ITO/P3HT contact does not limit the current; instead it is controlled by a space charge that accumulates due to the low charge carrier mobility in the polymer. An expression that provides a criterion to determine the validity of applying either the Richardson–Schottky thermionic emission model or the Fowler–Nordheim field emission model was deduced. It can be employed to determine the electrical field at which the transition from charge injection by thermionic emission to that by field emission for a given temperature and interface potential barrier height takes place. Our experimental data fit to the deduced expression. Theoretical limits of the model are also discussed. By considering the regions of the current-voltage curves where field emission or thermionic emission was applicable, the interface potential barriers were estimated, respectively. Hence, conclusions on whether the current-voltage behavior of the devices was contact limited or bulk limited could be drawn.
Chemical doping of graphene with small boron nitride (BN) domains has been shown to be an effective way of permanently modulating the electronic properties in graphene. Herein we show a facile method of growing large area graphene doped with small BN domains on copper foils using a single step CVD route with methane, boric acid powder and nitrogen gas as the carbon, boron and nitrogen sources respectively. This facile and safe process avoids the use of boranes and ammonia. Optical microscopy confirmed that continuous films were grown and Raman spectroscopy confirmed changes in the electronic structure of the grown BN doped graphene. Using XPS studies we find that both B and N can be substituted into the graphene structure in the form of small BN domains to give a B-N-C system. A novel structure for the BN doped graphene is proposed.
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