Photoinduced Charge Transfer across the Interface between Organic Molecular Crystals and Polymers

Abstract

Photo-induced charge transfer of positive and negative charges across the interface between an ordered organic semiconductor and a polymeric insulator is observed in the field-effect experiments. Immobilization of the transferred charge in the polymer results in a shift of the field-effect threshold of polaronic conduction along the interface in the semiconductor, which allows for direct measurements of the charge transfer rate. The transfer occurs when the photon energy exceeds the absorption edge of the semiconductor. The direction of the transverse electric field at the interface determines the sign of the transferred charge; the transfer rate is controlled by the field magnitude and light intensity.

Pursuing Polymer Dielectric Interfacial Effect in Organic Transistors for Photosensing Performance Optimization

“…It also should be noted that for our p‐type OFETs, V th positive shifted along with light intensity, which means that the hole density increased under illumination. This finding suggests that the lowest unoccupied molecular orbital energy levels of the OSCs march with these of the polymer dielectrics, while the highest occupied molecular orbital energy levels of the OSCs are far higher than those of the dielectrics 21, 25, 28. Electrons in photoexcitons are thus allowed to transfer from the OSCs to the polymer dielectrics, leaving holes conducting in the OSCs, which make the OFETs exhibit a photoinduced V th positive shift.…”

“…When the illumination wavelength is below the peak, the energy of the incident photons into the DNTT exceeds the band gap energy of the semiconductor, leading to the generation of photoexcitons. These results indicate that the stimulation of illumination to the interfacial effect is achieved through the photogenerated hole–electron pairs in the OSCs 21. In the following research, white light with broad wavelengths, which covers the UV–Vis absorbance peaks of all used OSCs, is employed.…”

“…The Λ‐shaped variation can be explained as follows: for the OFETs with PLA or PVA dielectric, appropriate interfacial traps are formed due to their decent dipole moments, and distributions of charge carriers in the devices achieve dynamic equilibriums between transporting in the conducting channels and being trapped near the interfaces 13, 22. Photogenerated charge carriers then fill the traps and supplement the conducting channels, leading to significant enhancement of OFET performance under illumination compared to performance in the dark; for χPVA‐DNTT‐OFET with a low dipole moment, the interfacial trapping is rather weak and the conducting channel is fully filled with charge carriers 11, 12, 21. The I DS of the device is high even in dark, so the effect of photoexcitons on the device performance is rather limited; while for PAN‐DNTT‐OFET which possesses a large dipole moment, photogenerated charge carriers would be continuingly confined by the strong interfacial traps, leading to remaining low I DS under illumination.…”

“…For example, Scanning Kelvin probe microscopy was employed to directly observe the charge protein on the interfaces in lateral organic transistors 17, 18, 19. OFETs with OSC single crystals and a parylene dielectric were also used to study photoinduced charge transfer across the interface 20, 21. Several profiles of the interfacial effect were revealed based on these investigations, primarily including: (a) shallow trap of charge carriers in OSC by the weak intermolecular interaction from the dielectric, leading to a mobility (μ) decrease for the OFET,22 and (b) transfer of charge carriers across the interface from OSC to the dielectric and a deep trap by functional groups in the polymer, leading to a threshold voltage ( V th ) change and bias stress effect for the device 17, 23.…”

Photosensitive and Flexible Organic Field‐Effect Transistors Based on Interface Trapping Effect and Their Application in 2D Imaging Array

“…It has been approved by the United States Food and Drug Administration (FDA) for human use 33, 34, 35, 36. We propose that an OPT device constructed using a PLA‐based gate dielectric would allow the polar groups of the PLA to interact with the organic semiconductor and induce interface charge trapping effect 37, 38, 39. The charge trapping effect has been generally considered a pitfall for organic electronics since it reduces charge mobilities and deteriorates device performances, but used here to enhance the photosensitivity of the fabricated OPT devices.…”