Molecular doping of organic semiconductors for high efficiency optoelectronic devices

Molecular doping of organic semiconductors for high efficiency optoelectronic devices

Internship Description

Doping of organic semiconductors plays a fundamental role to overcome typical limitations observed in organic electronic devices. Organic light-emitting diodes (OLEDs) and organic solar cells (OSC) benefits for instance of the introduction of highly conducting injection layers, while high conductivity is one of the basic requirements for organic thermoelectric materials. Organic field-effect transistors (OFETs), on the other hand, are almost entirely based on intrinsic materials and doping has been mainly employed to pattern areas close to the contacts in order to improve charge injection.1

Beside the investigation of high degree of doping, ultralow doping has been recently attracting great interest, with the aim of directly dope the devices active layer that were usually based on intrinsic organic semiconductors. OSC containing small weight percentage of molecular dopants in the bulk heterojunction were found to display an increased short-circuit current (Jsc) and hence higher power conversion efficiency (PCE), when compared to their intrinsic counterpart.2 OLEDs have been reported with improved performance and device color modulation with dopant concentration was reported.3 A similar approach has been employed for OFETs, where extremely high mobilities, beyond the highest reported in literature, have been reported for organic semiconductors blended with low concentrations of dopants.4–6

These latter approaches are based on the addition of low fractions of dopants (
£ 1-2 mol%), hence providing a different scenario from that of highly doped conducting layers. Strong efforts have been spent in the understanding of doping in organic semiconductors, both from a chemical and physical point of view, providing hence guidelines for the synthesis and application of more effective dopants. Recently, Lewis acid have been reported to show promising features as dopants for solution-processed polymers and small molecules.4 Here we propose a systematic study of different types of Lewis acids to investigate the potentiality of this doping strategy for organic field-effect transistors. Different processing routes and compositions will be studied in order to establish relevant structure/processing/property interrelationships.

Deliverables/Expectations

1. Prepare solutions and learn coating methods for the formation of solution
processable thin films. [Month 1-6]

2. Learn how to prepare and measure organic electronic devices, such as
high emitting diodes, organic solar cells and field-effect transistor. [Month 3]

3. Study the influence of dopants in structural and optical properties of organic
semiconductors and devices. [Month 4]

4. Prepare project updates reports and presentation. [Month 6]​ 

Faculty Name

Thomas Anthopoulos

Field of Study

​​Materials science