Excited state dynamics and exciton diffusion in triphenylamine/dicyanovinyl push\u2013pull small molecule for organic optoelectronics

Benedito A L Raul,Thomas L C Jansen,Yuriy N Luponosov,Nikolay M Surin,Wenyan Yang,Olivier Douhéret,Sergei A Ponomarenko,Maxim S Pshenichnikov,Jie Min

doi:10.1038/s41598-020-78197-2

Abstract

Triphenylamine-based small push–pull molecules have recently attracted substantial research attention due to their unique optoelectronic properties. Here, we investigate the excited state de-excitation dynamics and exciton diffusion in TPA-T-DCV-Ph-F small molecule, having simple chemical structure with asymmetrical architecture and end-capped with electron-withdrawing p-fluorodicyanovinyl group. The excited state lifetime in diluted solutions (0.04 ns in toluene and 0.4 ns in chloroform) are found to be surprisingly shorter compared to the solid state (3 ns in PMMA matrix). Time-dependent density functional theory indicates that this behavior originates from non-radiative relaxation of the excited state through a conical intersection between the ground and singlet excited state potential energy surfaces. Exciton diffusion length of ~ 16 nm in solution processed films was retrieved by employing time-resolved photoluminescence volume quenching measurements with Monte Carlo simulations. As means of investigating the device performance of TPA-T-DCV-Ph-F, we manufactured solution and vacuum processed bulk heterojunction solar cells that yielded efficiencies of ~ 1.5% and ~ 3.7%, respectively. Our findings demonstrate that the short lifetime in solutions does not hinder per se long exciton diffusion length in films thereby granting applications of TPA-T-DCV-Ph-F and similar push–pull molecules in vacuum and solution processable devices.

Highlights

Triphenylamine-based small push–pull molecules have recently attracted substantial research attention due to their unique optoelectronic properties
We report on the excited state relaxation pathways and exciton diffusion dynamics in a TPA/ DCV based small molecule (TPA-T-DCV-Ph-F)
We show that the excited state lifetime in solutions amounts to ~ 0.04 ns in toluene and ~ 0.4 ns in chloroform, which is substantially shorter than ~ 3 ns in the poly(methyl methacrylate) (PMMA) matrix

Summary

Introduction

Triphenylamine-based small push–pull molecules have recently attracted substantial research attention due to their unique optoelectronic properties. Triphenylamine (TPA) based small molecules with the push–pull character have attracted a lot of attention for showing great potential as donor materials in organic solar cells (OSCs)[1,2] and hole transporting layers in perovskite solar c ells[3]. We show that the excited state lifetime in solutions amounts to ~ 0.04 ns in toluene and ~ 0.4 ns in chloroform, which is substantially shorter than ~ 3 ns in the PMMA matrix This unusual behavior is assigned to excited state non-radiative depopulation via conical intersection between the ground and excited state potential energy surfaces. By combining time-resolved photoluminescence (PL) volume quenching experiments with Monte-Carlo simulations, the exciton diffusion length in solution processed films of TPA-T-DCV-Ph-F is obtained as ~ 16 nm and found to be limited by the energetic disorder. The obtained results suggest that the TPA-T-DCV-Ph-F molecule offers promising properties for organic optoelectronics provided that the energetic disorder is reduced

Methods

Results

Conclusion