Dipole-induced conductivity enhancement by n-type inclusion in a p-type system: α-Fe₂O₃–PEDOT:PSS nanocomposites

Abstract

Hematite (α-Fe2O3) nanoparticles of two different shapes but of same size (ca. 40 nm) were dispersed in PEDOT:PSS matrices in various concentration ranges (0-7 wt%) to study the consequent changes in conductivity in the dark and under solar illumination conditions. Within a distinct range of concentration, a distinct increase in the conductivity was observed for both spherical and cubical particle population. We ascribed this effect to the generalized Poole-Frenkel theory of conduction in conjunction with the basic depletion width properties of heterojunctions and electrostatic dipole moments, and verified our assumptions through data fitting. A difference in conductivity between sphere- and cube-based α-Fe2O3-PEDOT:PSS nanocomposites was also observed and ascribed to the electrostatic edge effect on the nanoparticles. The dispersion of α-Fe2O3 nanocrystals was confirmed by high-resolution electron microscopy, whereas the electrical properties and modulations thereof were followed by recording current-voltage characteristics.

Enhanced Dispersion of TiO2 Nanoparticles in a TiO2/PEDOT:PSS Hybrid Nanocomposite via Plasma-Liquid Interactions

“…After plasma treatment the pH of the solution increased slightly to 4.7. Depending on IS, this is within the pH range where electrostatic stabilisation is less effective, and in other reports, pH values around 2 were typically required for NP stabilisation in PEDOT:PSS 31 32 33 34 . The plasma treatment has clearly shown the ability to improve the dispersion of the NPs.…”

“…which was attributed to the insulating nature of the particles. However Raccis et al 32 observed that, within a very narrow range of concentrations (~1.2%), the conductivity of PEDOT-PSS could be increased up to eight-fold after NP inclusion. Understanding PEDOT:PSS conduction mechanisms is a significant challenge in the search for enhanced or selectable conductivity and resistance to degradation.…”

“…The use of TiO 2 31 and other n-type NPs (e.g. α-Fe 2 O 3 32 ) for conductivity modulation of PEDOT:PSS has been reported along with the tailoring of TiO 2 electronic properties (reduced bandgap, fermi-level shifting) through surface modification with polymer/dye interfaces 33 48 and doping 16 . It is unlikely that significant electronic structure modification has occurred in our case due to plasma treatment as very minor change (except intensity) was observed in UV-vis absorption spectra.…”

“…As an n-type conductor in a p-type material, the TiO 2 NPs would be isolated from the conductive networks and not be expected to automatically enhance the polymer conductivity. Charge confinement on the NP surface 56 57 and the resultant surface electric field extending into the polymer between NPs, would impact on polymer mobility through a complex exponential dependence on field strength 32 . Where the fields are moderate or low, the mobility would be enhanced and the degree of enhancement would be dependent on NP-NP spacing, i.e.…”

Optimization of SiO 2 –TiO 2 nanocomposite in hole‐transporting layer (PEDOT:PSS) for enhanced performance of planar Si‐based hybrid solar cells

“…However, it is evident from the literature that the embedment of particles of size between 20 and 50 nm is optimum for better effect on the properties of the organic layer. Since the thickness of the organic layer is limited, larger particle sizes deteriorate the layer, while smaller particle sizes are more difficult to synthesize 35,36,39,40 …”