Revealing the Impact of Heat Generation Using Nanographene-Based Light-Emitting Electrochemical Cells.

Elisa Fresta,Juan Cabanillas-Gonzalez,Jacopo Dosso,Davide Bonifazi,Rubén D. Costa

doi:10.1021/acsami.0c06783

Abstract

Self-heating in light-emitting electrochemical cells (LECs) has been long overlooked, while it has a significant impact on (i) device chromaticity by changing the electroluminescent band shape, (ii) device efficiency because of thermal quenching and exciton dissociation reducing the external quantum efficiency (EQE), and (iii) device stability because of thermal degradation of excitons and eliminate doped species, phase separation, and collapse of the intrinsic emitting zone. Herein, we reveal, for the first time, a direct relationship between self-heating and the early changes in the device chromaticity as well as the magnitude of the error comparing theoretical/experimental EQEs-that is, an overestimation error of ca. 35% at usual pixel working temperatures of around 50 °C. This has been realized in LECs using a benchmark nanographene-that is, a substituted hexa-peri-hexabenzocoronene-as an emerging class of emitters with outstanding device performance compared to the prior art of small-molecule LECs-for example, luminances of 345 cd/m2 and EQEs of 0.35%. As such, this work is a fundamental contribution highlighting how self-heating is a critical limitation toward the optimization and wide use of LECs.

Highlights

Light-emitting electrochemical cells (LECs) are simple and low-cost solid-state emissive devices that consist of a thin film active layer sandwiched between two air-stable electrodes.[1,2] The active layer comprises a blend of mobile ions and an electroactive emitter
We reveal, for the first time, a direct relationship between self-heating and the early changes of the device chromaticity as well as the magnitude of the error comparing theoretical/experimental EQEs – i.e., overestimation error of ca. 35 % at usual pixel working temperatures of around 50 °C. This has been realized in LECs using a benchmark nanographene – i.e., a substituted hexa-peri-hexabenzocoronene – as an emerging class of emitters with outstanding device performance compared to the prior-art of small molecule LECs – e.g., luminances of 345 cd/m2 and EQEs of 0.35%
We have further prepared thin-films with only 1 and with blends of 1 with the polymer electrolyte mixture used in devices – i.e., 1:PS:PEO:LiOTf in a mass ratio 10:0.9:2.6:0.78, being PS, PEO, and LiOTf (Lithium Triflate); see Supporting Information (SI) for more details

Summary

Introduction

Light-emitting electrochemical cells (LECs) are simple and low-cost solid-state emissive devices that consist of a thin film active layer sandwiched between two air-stable electrodes.[1,2] The active layer comprises a blend of mobile ions and an electroactive emitter. This work states the relevance of self-heating as a critical limitation in the optimization of both, device performance (color and efficiency) and device application (medicine, labelling, etc.), regardless of the type of emitter

Results and Discussion

Conclusions

Experimental Section

Device fabrication and characterization