Electric-field quenching of optically detected magnetic resonance in a $\pi$-conjugated polymer

TL;DR

This study investigates how electric fields influence optically detected magnetic resonance in a conjugated polymer, revealing that strong fields quench the ODMR signal and suggesting exciton-charge interactions as key dissociation mechanisms.

Contribution

It demonstrates electric-field-induced quenching of ODMR in conjugated polymers and identifies a saturation effect at high fields, highlighting a new understanding of charge carrier dynamics.

Findings

ODMR signal is quenched by electric fields in polymer films.

Quenching saturates at electric fields above 1 MV/cm.

Exciton-charge interactions may dominate carrier dissociation in organic electronics.

Abstract

Electric fields are central to the operation of optoelectronic devices based on conjugated polymers since they drive the recombination of electrons and holes to excitons in organic light-emitting diodes but are also responsible for the dissociation of excitons in solar cells. One way to track the microscopic effect of electric fields on charge carriers formed under illumination of a polymer film is to exploit the fluorescence arising from delayed recombination of carrier pairs, a process which is fundamentally spin dependent. Such spin-dependent recombination can be probed directly in fluorescence, by optically detected magnetic resonance (ODMR). Depending on the relative orientation, an electric field may either dissociate or stabilize an electron-hole carrier pair. We find that the ODMR signal in a polymer film is quenched in an electric field, but that, at fields exceeding 1 MV/cm, this quenching saturates. This finding contrasts the complete ODMR suppression that was previously observed in polymeric photodiodes, indicating that exciton-charge interactions---analogous to Auger recombination in crystalline semiconductors---may constitute the dominant carrier-pair dissociation process in organic electronics.