Faculty Publications
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Item Enhancement in fluorescence quantum yield of MEH-PPV:BT blends for polymer light emitting diode applications(Elsevier B.V., 2018) K M, K.M.; Satyanarayan, M.N.; Umesh, G.We have investigated the effect of blending electron deficient heterocycle Benzothiadiazole (BT) on the photo-physical properties of conjugated polymer Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Quantum yield (QY) value has been found to increase from 37% for pure MEH-PPV to 45% for an optimum MEH-PPV:BT blend ratio of 1:3. This can be attributed to the efficient energy transfer from the wide bandgap BT (host) to the small bandgap MEH-PPV (guest). The FTIR spectrum of MEH-PPV:BT blended thin film indicates suppression of aromatic C-H out-of-plane and in-plane bending, suggesting planarization of the conjugated polymer chains and, hence, leading to increase in the conjugation length. The increase in conjugation length is also evident from the red-shifted PL spectra of MEH-PPV:BT blended films. Single layer MEH-PPV:BT device shows lower turn-on voltage than single layer MEH-PPV alone device. Further, the effect of electrical conductivity of PEDOT:PSS on the current-voltage characteristics is investigated in the PLED devices with MEH-PPV:BT blend as the active layer. PEDOT:PSS with higher conductivity as HIL reduces the turn on voltage from 4.5 V to 3.9 V and enhances the current density and optical output in the device. © 2018 Elsevier B.V.Item New cyanopyridine based conjugated polymers carrying auxiliary electron donors: From molecular design to blue emissive PLEDs(Elsevier Ltd, 2020) Pilicode, N.; Naik, P.; K M, K.M.; Acharya, M.; Satyanarayan, M.N.; Vasudeva Adhikari, A.V.Three new D-A (Donor-Acceptor) configured conjugated polymers, i.e. PPy1-3, centered on strong electron accepting cyanopyridine scaffold carrying varied auxiliary donors, viz. phenylene (PPy1), biphenyl (PPy2), and fluorene (PPy3) were designed and synthesized as blue emitters for PLEDs. The new polymers were subjected to spectral, thermal, photophysical and electrochemical characterization. Also, computational studies (DFT) were performed on the repeating units of polymer using Turbomole 7.2 V software package at the B3LYP/TZVP hybrid levels. Further, their weight average molecular masses were found to be 38.8 kDa, 38.9 kDa and 57.7 kDa, respectively as determined by GPC technique. Furthermore, the new polymers PPy1-3, were shown to be stable thermally up to 308–374 °C. Evidently, they exhibited good photophysical behavior with their optical energy band gaps of 2.53–2.64 eV. Finally, the polymers PPy1-3 were employed as an active emissive layer in standard ITO/PEDOT:PSS/Polymer/Al configured PLEDs. Interestingly, at 12 V all the newly fabricated devices exhibit a stable blue characteristic electroluminescence with low threshold voltages of 3.40–5.20 V, confirming an efficient injection of electrons in the diodes. From the results, it is clear that, the polymers PPy1-3, can be considered as prospective blue light emitters for PLED application. © 2019 Elsevier Ltd