Efficient Blue Polymer Light‐Emitting Diodes with Electron‐Dominated Transport Due to Trap Dilution

Abstract

As is common for many conjugated polymers used in light‐emitting diodes (PLEDs), the charge transport in blue‐emitting polyspirobifluorene (PSF) copolymerized with the hole transport unit – N,N,N′N′‐tetraaryldiamino (TAD) biphenyl – is dominated by holes. Although the free electron mobility is an order of magnitude higher than the hole mobility, the electron transport is strongly hindered by traps. By diluting PSF‐TAD with the wide band gap polymer poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (PFO), the effect of electron trapping can be nearly eliminated. As a result, the transport in the PSF‐TAD:PFO blend becomes electron dominated. Due to the higher electron mobility, PLEDs made from these blends exhibit higher current and light‐output as compared to hole‐dominated PLEDs made from pristine PSF‐TAD. The reduced amount of electron traps enhances their efficiency from 2 cd A−1 for the hole‐dominated PLED to 5.3 cd A−1 for the electron‐dominated blend PLED.

Ferroelectric Diode Effect with Temperature Stability of Double Perovskite Bi2NiMnO6 Thin Films

“…The cubic phase of LNO acted as an n-type semiconductor to release electrons, while the nano-crystallinity of the BNMO layer defects acted as a hole-absorbing electron [23][24][25].The Schottky emission mechanism is determined by the linear relationship of Ln(I) versus V 1/2 [26,27]. If the relationship is linear, this is due to the thermionic emission by holes, vacancies and defects [28][29][30][31][32], respectively. The restricted behavior of the interface and the hole trapping behavior are considered to be a case of the Schottky emission mechanism, as expected with linear relationship of Ln(I) versus V 1/2 for the BNMO/LNO/p-Si heterojunction (see the inset of Figure 5b).…”

Low-Cost and Green Fabrication of Polymer Electronic Devices by Push-Coating of the Polymer Active Layers

“…It is worth noticing that well-performing PLEDs with active layer thicknesses over 300 nm cannot be easily obtained by spin-coating and their fabrication in standard architecture has rarely been reported. 36,37 Moreover, to fabricate the 200 nm devices, 3 μL of F8BT solution at a concentration of 10 mg/mL and 80 μL of 20 mg/mL solution were used in the push-coating and spin-coating processes, respectively. Fabricating PLEDs by push-coating therefore reduces used active layer material and solvent amounts by factors of 50 and 20, respectively, as compared to those in spin-coating.…”

“…When the push-coated device was subjected to the same annealing process as that for 2, we recorded a moderate decrease of the performances (device 4) with respect to those of the untreated push-coated device (3), together with a roughness diminution from 2.8 to 1.5 nm, confirming the optimal morphology of the as-deposited push-coated film. It is worth noticing that well-performing PLEDs with active layer thicknesses over 300 nm cannot be easily obtained by spin-coating and their fabrication in standard architecture has rarely been reported. , Moreover, to fabricate the 200 nm devices, 3 μL of F8BT solution at a concentration of 10 mg/mL and 80 μL of 20 mg/mL solution were used in the push-coating and spin-coating processes, respectively. Fabricating PLEDs by push-coating therefore reduces used active layer material and solvent amounts by factors of 50 and 20, respectively, as compared to those in spin-coating.…”

Large‐Area Printed Display Based on Green Solvent Processable Blue Light‐Emitting Conjugated Polymer

“…[26][27][28][29] However, research on the ecofriendly solvent-processed polymer light-emitting diodes (PLEDs) has been rarely reported due to the limited solubility of LCPs resulted by rigid aromatic backbone and complex intermolecular interactions, [30] especially for the blue PLEDs, [31] where achieving high-efficient and stable electroluminescence (EL) remain huge challenges. [32][33][34] On the other hand, although the classification and ranking of green solvents varies slightly from organization to organization, they all make qualitative assessment according to the criteria: low health hazard, high safety, and small environmental impact. [35,36] From this perspective, bio-based solvents seem like to be one of the ideal choices for solution-based printed electronics.…”