Mapping of Charge Distribution in Organic Field-Effect Transistors by Confocal Photoluminescence Electromodulation Microscopy

Abstract

A novel method for mapping the charge density spatial distribution in organic field-effect transistors based on the electromodulation of the photoluminescence is demonstrated. In field-effect transistors exciton quenching is dominated by exciton-charge carrier interaction so that it can be used to map the charge distribution in different operating conditions. From a quantitative analysis of the photoluminescence quenching, the thickness of the charge carrier accumulation layer is derived. The injection of minority charge carriers in unipolar conditions is unexpectedly evidenced, which is not displayed by the electrical characteristics.

High-resolution photoluminescence electro-modulation microscopy by scanning lock-in

“…A plethora of techniques have been developed to obtain a direct microscopic spatial mapping of the electrostatics in OFETs [14][15][16][17][18] . The most advanced of these is scanning Kelvin-probe microscopy 19 , which senses the interaction of the local electrical potential with an AFM tip 15,[20][21][22][23][24] .…”

“…In particular, it cannot be used to study buried interfaces in multilayer devices or to access the area below metallic top contacts. Techniques based on optical probes 14,16,18,[25][26][27][28] present an alternative that can access different layers individually, by taking advantage of the distinct optical properties of each layer 29 . Moreover, if transparent substrates are used, they can also reach areas below metal contacts to probe the mechanisms of charge injection.…”

“…Recently, we introduced Photoluminescence Electro-Modulation Microscopy (PLEM) as a technique that allows the direct mapping of the charge density distribution in OFETs 18 . The presence of charges is detected by the charge-induced quenching of excitons 31 .…”

“…PLEM was successfully used to map the charge accumulation and depletion regions in active OFETs 18 . However, the technique would be even more valuable, if the morphology-dependent details of the local charge accumulation distribution could be resolved with maximized signalto-noise ratio (SNR), which was not possible with these already-reported measurements.…”

Direct visualization of polarization reversal of organic ferroelectric memory transistor by using charge modulated reflectance imaging

“…There are many ways to study the carrier behaviors in the OFET channel microscopically. Among them are microscopic scanning surface potential measurement [34][35][36], electric field induced optical second harmonic generation measurement [11,20], PL imaging [37] and others [38][39][40][41][42]. CMS imaging also provides a way to visualize carrier behavior in FET channel [43][44][45].…”