Substitution effect on carbazole-centered donors for tuning exciplex systems as cohost for highly efficient yellow and red OLEDs
Journal
Materials Chemistry Frontiers
Journal Volume
5
Journal Issue
13
Pages
5044-5054
Date Issued
2021
Author(s)
Abstract
Three new carbazole-based hole-transporting materials PTCz-9′Cz, PTCz-3′TCz, and PTCz-NTol2 were synthesized, characterized, and examined for the propensity of exciplex formation with the electron-transporting material PO-T2T. Through enhancing the electron-donating ability of the substituents, the HOMO energy of the donors, PTCz-9′Cz, PTCz-3′TCz, and PTCz-NTol2, increased from -5.59 eV, -5.40 eV to -5.02 eV, respectively. Consequently, the photoluminescence of the corresponding exciplex is red-shifted, giving blue, green and orange emissions. Among these three donor?:?acceptor blends, the device utilizing PTCz-9′Cz?:?PO-T2T (2?:?1) as the emitting layer rendered the best device efficiency with a maximum external quantum efficiency (EQEmax) of 10.9%. Then, the two D-A-D-configurated fluorescent emitters, iCzPNT and iCzBTh2CN, with different electron-accepting cores were introduced as the emitting guests of this exciplex-forming cohost system to explore the possibility of high efficiency OLEDs with all organic materials. The device with 10 wt% iCzPNT as the dopant was found to give yellow electroluminescence (EL) (λEL= 578 nm and CIE (0.53, 0.46)) with an EQEmax of 7.8%, whereas the device with 10 wt% iCzBTh2CN as the dopant gave red EL (λEL = 618 nm and CIE (0.63, 0.37)) with an EQEmax of 8.0%. Thanks to the TADF feature of the exciplex-forming system, the energy transfer between the exciplex host and fluorescent guest proved to be a promising strategy to efficiently harvest the electro-generated singlet and triplet excitons for giving high efficiency OLED devices. This work highlights the versatility of introducing a substitution effect onto the electron donor to manipulate the emission wavelength of the exciplex and facilitate the identification of a good exciplex-forming system for serving as the cohost of tailor-made fluorescent emitters. This journal is ? the Partner Organisations.
Subjects
Electroluminescence
Electrons
Energy transfer
Fluorescence
Organic light emitting diodes (OLED)
Polycyclic aromatic hydrocarbons
Red Shift
Electron transporting materials
Electron-donating ability
Emission wavelength
External quantum efficiency
Fluorescent emitters
Hole-transporting materials
Singlet and triplet excitons
Substitution effect
High energy forming
SDGs
Type
journal article