Chen L.-MLin I.-HYou Y.-CWei W.-CTsai M.-JHung W.-YKEN-TSUNG WONG2022-04-252022-04-25202120521537https://www.scopus.com/inward/record.uri?eid=2-s2.0-85108969104&doi=10.1039%2fd1qm00425e&partnerID=40&md5=c8da7e4183449fde6c6fdbe6e4470addhttps://scholars.lib.ntu.edu.tw/handle/123456789/606894Three 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.ElectroluminescenceElectronsEnergy transferFluorescenceOrganic light emitting diodes (OLED)Polycyclic aromatic hydrocarbonsRed ShiftElectron transporting materialsElectron-donating abilityEmission wavelengthExternal quantum efficiencyFluorescent emittersHole-transporting materialsSinglet and triplet excitonsSubstitution effectHigh energy forming[SDGs]SDG7journal article10.1039/d1qm00425e2-s2.0-85108969104