The formation of polymer-dopant aggregates as a possible origin of limited doping efficiency at high dopant concentration

TL;DR

This paper investigates how the formation of polymer-dopant aggregates at high dopant concentrations hampers doping efficiency in organic semiconductors, combining microscopy and spectroscopic analyses to understand the underlying mechanisms.

Contribution

It provides a detailed analysis of aggregate formation and its impact on doping efficiency, highlighting the need for improved doping strategies in organic semiconductors.

Findings

Aggregate formation correlates with reduced conductivity at high dopant levels

Microscopy reveals morphological changes associated with doping limits

Spectroscopy confirms composition of dopant-polymer aggregates

Abstract

The polymer (PBDTTT-c) p-doped with the molecular dopant (Mo(tfd-COCF3)3) exhibits a decline in transport properties at high doping concentrations, which limits the performance attainable through organic semiconductor doping. Scanning Electron Microscopy is used to correlate the evolution of hole conductivity and hopping transport activation energy with the formation of aggregates in the layer. Transmission Electron Microscopy with energy-dispersive X-ray analysis along with liquid-state Nuclear Magnetic Resonance experiments are carried out to determine the composition of the aggregates. This study offers an explanation to the limited efficiency of doping at high dopant concentrations and reinforces the need to increase doping efficiency in order to be able to reduce the dopant concentration and not negatively affect conductivity.