Electrically Driven MOF-Based Blue to Yellow-White Tunable Light Emitting Diodes

In this study, the Gadolinium metal based organic framework (Gd-MOF) is synthesized using the hydrothermal route. The as-synthesized material is dissolved in solvent and used to fabricate organic light emitting diodes (OLEDs) in the device structure ITO/PEDOT:PSS/poly-TPD/Gd-MOF/TPBi/LiF/Al. The luminance of Gd-MOF based OLED is found to be of 35.9 cd/m2 at 8 V. In the emission spectra, three peaks viz. blue, green and red are obtained at 425 nm, 480 nm and 600 nm respectively with excitation at 325 nm. By tuning the operating voltage, we have been able to achieve a white emission from our device in which the peak at 425 nm arises due to poly-TPD however the other two peaks at 480 nm and 600 nm come from Gd-MOF respectively. The voltage dependent study of the electroluminescence spectra of our device indicates that poly-TPD peak intensity increases significantly with the increase in voltage and exceeds the intensity of Gd-MOF peak (488 nm) after 7.5 V. It is also observed that the luminance intensities of Gd-MOF peaks tend to be saturated after 7 V. This is due to the fact that the electron-hole recombination region of our device expands with increasing operating voltage. At lower voltage, the radiative recombination zone is mainly confined within the Gd-MOF region however with increasing voltage the exciton accumulation gradually expands to the Poly-TPD region resulting in a gradual increase in the poly-TPD emission keeping the Gd-MOF emission as to be saturated.