Ultrafast charge transfer in a PDY-132:F8T2 polymer blend for lowering turn on voltage in OLEDs: implications of low Urbach energy and faster photoluminescence dynamics

Abstract

PDY-132 and its blends with different concentrations of poly(9,9-dioctylfluorenyl-co-3 bithiophene) F8T2 were employed as an emissive matrix for organic light-emitting devices (OLEDs). The Urbach energy lies well below 50 meV, which reflects the reduced energetic disorder, signifying the efficient charge transfer in the polymer blends. The photoluminescence time constants vary proportionally from 0.89–0.35 ns as a function of the acceptor concentration in the FRET pairs, reflecting 2.5× faster charge transfer in the blends than in PDY-132. The Förster radius of 57 Å, decay time of 0.89 ns, quenching constant of 0.12 μM⁻¹, quenching rate constant of 1.4 × 10⁸ μM⁻¹ s⁻¹, charge transfer lifetime of 6.21 ns to 2.38 ns, and non-radiative transfer rate of 4.0 × 10⁸ s⁻¹ exhibit the excellent parameters for efficient charge transfer within the blend, resulting in lowering of the turn on voltage by 67% from 6.5 V to 2 V. The current density of 3 mA cm⁻² increases to 25 mA cm⁻², an increase of 8× with increasing concentration of F8T2.