H-aggregate analysis of P3HT thin films-Capability and limitation of photoluminescence and UV/Vis spectroscopy

Abstract

Polymer morphology and aggregation play an essential role for efficient charge carrier transport and charge separation in polymer-based electronic devices. It is a common method to apply the H-aggregate model to UV/Vis or photoluminescence spectra in order to analyze polymer aggregation. In this work we present strategies to obtain reliable and conclusive information on polymer aggregation and morphology based on the application of an H-aggregate analysis on UV/Vis and photoluminescence spectra. We demonstrate, with P3HT as model system, that thickness dependent reflection behavior can lead to misinterpretation of UV/Vis spectra within the H-aggregate model. Values for the exciton bandwidth can deviate by a factor of two for polymer thicknesses below 150 nm. In contrast, photoluminescence spectra are found to be a reliable basis for characterization of polymer aggregation due to their weaker dependence on the wavelength dependent refractive index of the polymer. We demonstrate this by studying the influence of surface characteristics on polymer aggregation for spin-coated thin-films that are commonly used in organic and hybrid solar cells.

Printed, cost-effective and stable poly(3-hexylthiophene) electrolyte-gated field-effect transistors

“…Indeed, the optical properties of P3HT in the solid state are wellcharacterized so they can be used to assess the supramolecular structure of the film. [11][12][13][14] To this end UV-Vis but also Raman characterization of P3HT can be used to establish correlations between the optical and electronic performance level of the film and its structure. These pieces of information can be eventually used to optimize the film processing conditions.…”

Efficient energy transfer mitigates parasitic light absorption in molecular charge-extraction layers for perovskite solar cells

“…For example, weaker interchain (through-space) interactions and stronger intrachain (through-bond) interactions have been observed when P3HT forms a two-phase morphology of interconnected crystalline and amorphous phases, compared with films comprising a chain-extended morphology of layered stacks exhibiting high torsional disorder 66 , 67 . The evolution of the PL lineshape we observe for P3HT films on MAPbI 3 :quartz thus most likely derives from the presence of an amorphous phase formed under some conditions near the interface to MAPbI 3 , which causes a decrease in interchain interaction compared to the films deposited on a smoother quartz substrate 42 , 68 . As Ehrenreich et al 42 pointed out, such amorphous polymer structure may energetically enhance the HOMO (highest-occupied molecular orbital) level near the interface 69 , which can affect charge transport and injection 70 .…”

“…The evolution of the PL lineshape we observe for P3HT films on MAPbI 3 :quartz thus most likely derives from the presence of an amorphous phase formed under some conditions near the interface to MAPbI 3 , which causes a decrease in interchain interaction compared to the films deposited on a smoother quartz substrate 42 , 68 . As Ehrenreich et al 42 pointed out, such amorphous polymer structure may energetically enhance the HOMO (highest-occupied molecular orbital) level near the interface 69 , which can affect charge transport and injection 70 . We observe here that such an amorphous phase seems less prominent for the thinnest polymer films (~40 nm) on MAPbI 3 , which are produced at higher spin speeds.…”

“…Both transport pathways are sensitive to the arrangement of the polymer chains, which differs between polymers in solution and in thin films 36 , and is strongly influenced by film morphology 37 – 41 . In addition, chain morphology affects electronic energy levels, which may complicate their alignment with other conducting layers in the device 42 . Proper understanding of polymer structures within the transport layer, and in particular, at interfaces to other layers such as MHP films, is therefore critical for the development of efficiently working devices.…”

Effect of Different Ionic Surfactants on the Structural, Photophysical, and Morphological Properties of Water‐Based P3HT:PCBM Nanoparticle Dispersions and Films

“…This deviation might be ascribed to undesired effects/phenomena such as light scattering, that strongly influence absorption spectra and thus the resulting parameters, as demonstrated by Ehrenreich. [ 63 ]…”