Singular Temperatures Connected to Charge Transport Mechanism Transitions in Perylene Bisimides from Steady-State Photocurrent Measurements

Abstract

Perylene bisimides (PBIs) are n-type semiconducting and photogenerating materials widely used in a variety of optoelectronic devices. Particularly interesting are PBIs that are simultaneously water-soluble and liquid-crystalline (PBI-W+LC), and thus attractive for the development of high-performing easy-processable applications in biology and "green" organic electronics. In this work, singular temperatures connected to charge transport mechanism transitions in a PBI-W+LC derivative are determined with high accuracy by means of temperature-dependent photocurrent studies. These singular temperatures include not only the ones observed at 60 ºC and 110 ºC, corresponding to phase transition temperatures from crystalline to liquid crystalline (LC) and from LC to the isotropic phase respectively, as confirmed by differential scanning calorimetry (DSC), but also a transition at 45 ºC, not observed by DSC. By analyzing the photocurrent dependence simultaneously on temperature and on light intensity, this transition is interpreted as a change from monomolecular to bimolecular recombination. These results might be useful for other semiconducting photogenerating materials, not necessarily PBIs or even organic semiconductors, which also show transport behavior changes at singular temperatures not connected with structural or phase transitions.

Organic Optoelectronic Materials: Mechanisms and Applications

“…These experiments are performed on “sandwich”-type or “surface”-type samples (depending on the placement of the electrodes), and they involve measurements of photocurrent as a function of applied electric field, light intensity, temperature, ,,, magnetic field, , etc. , The experiment involves measurement of the total current under cw excitation of a sample ( I tot ), and the photocurrent ( I ph ) is then calculated as the difference between the total and the “dark” current ( I d ), I ph = I tot – I d , from which the dark conductivity and photoconductivity (σ d and σ ph , respectively) can be calculated using, for example, σ d (ph) = I d (ph) /( FS ), where F is the applied electric field, and S (in the case of the sandwich sample geometry) is the electrode area. If the sample is highly absorbing, a more sophisticated scheme of extracting “intrinsic” photoconductivity values is necessary. , An excellent overview of the steady-state photocurrent behavior depending on the sample geometry, electrodes, and external parameters can be found in ref .…”

“…The steady-state photocurrent dependence on light intensity can provide information about charge trapping and recombination (Section ). The temperature dependence of the photocurrent has been used as a sensitive probe of glass transition temperature in PR polymers and of phase transitions in PBI derivatives . The magnetic field dependence of the photocurrent revealed the mechanisms of spin-mixing responsible for spin-dependent charge carrier recombination in polymer-based BHJs …”

Aggregation Behavior and Electron‐Transfer Reaction of Dendritic Perylene Bisimide, Accompanied by the Formation of Highly Stable Anionic Radical Species

“…Monomers and aggregates of PBIs have great influence on the photochemical and electrochemical properties. Not only PBI concentration, but also solvent polarity, temperature, and pH can change the state of PBIs in solution . Several solvents (methanol, ethanol, acetonitrile, DMSO, DMF, N , N ‐dimethylacetamide and acetone) were chosen to study the effect of solvent effect on the spectra.…”

Relationship between Side‐Chain Polarity and the Self‐Assembly Characteristics of Perylene Diimide Derivatives in Aqueous Solution

“…Research into PDIs has mainly focused on their use in bulk. For example, the liquid crystalline behavior of this dye resulted in semiconducting and temperature‐responsive materials . Moreover, solvent‐free techniques were exploited to shape these dyes into well‐defined fibers and to prepare oriented nanoporous silica films .…”

“…For example, the liquid crystalline behavior of this dye resulted in semiconducting [19][20][21] and temperature-responsive materials. [22,23] Moreover,s olventfree techniques were exploited to shape these dyes into welldefined fibers [24] and to prepareo riented nanoporous silica films. [25] In contrastt oa dvances in bulk processing, the number of studies on PDIs in aqueous solution has been limited by their poor solubility.R ecent efforts have been made to improvet he aqueous solubility of PDIsb yi ntroducingh ydrophilic substituents at different positions on the perylene core.…”