Mi Jang, Minjung Lee, and co-workers clearly demonstrate how much the balancing surface hydrophobicity and polarizability of gate dielectrics is important to achieve excellent environmental, gate-bias stability, and mobility of organic field-effect transistors, specifically, based on pentacene layers grown on hydrophobicity-controlled fluorinated copolymer-treated dielectrics in article 1600284.
It is reported on the allocation effects of branched alkyl chains, when used as solubility and ordering enhancers of the conjugated donor–accepter (D–A) copolymer backbones, on the ordering and π–π overlapping of the copolymers, that drastically affect the electrical properties of organic field-effect transistors (OFETs). Triisopropylsilylethynyl-benzo[1,2-b:4,5-b′]dithiophene (TIPSBDT) and diketopyrrolopyrrole (DPP)-based copolymers, which have two linear alkyl spacers (methylene (C1) or butylene (C4)) between the DPP and side-substituent (C10H21)CH(C8H17), are synthesized by Suzuki cross-coupling. These copolymer films are spun cast onto a polymer-treated SiO2 dielectric surface, and some are further thermally annealed. The longer spacer, C4, is found to efficiently enhance the coplanarity and conjugation of the D–A backbone, while the C1 does not. The resulting C4-bridged TIPSBDT-DPP-based copolymer readily develops a superior π-extended layer on the dielectric surface; the edge-on chains with randomly oriented side chains can be closely packed with a short π-planar distance (d(010)) of 3.57 Å. Its properties are superior to those of the short spacer C1 system with d(010) ≈3.93 Å. The C4-bridged TIPSBDT-DPP copolymer films yield a field-effect mobility up to 1.2 cm2 V−1 s−1 in OFETs, 12 times as higher than that of the C1 spacer system.
A series of diketopyrrolopyrrole (DPP)-based copolymers, with DPP and bithiophene (BT) as the electron-acceptor and donor backbone units, respectively, are synthesized with branched alkyl side chains that are either directly coupled to the N-positions of DPP or separated by an alkyl ester group. The ester moieties in the side chains induce specific cohesive molecular interactions between these side chains, as compared to the alkyl-only side chains with weak van der Waals interactions. Structure analysis of the DPPBT-based copolymers demonstrated that the introduction of a proper alkyl ester spacer to the branched alkyl chains can shorten the π-π stacking distance between the DPPBT backbones down to 3.61 Å and promote the development of two-dimensionally extended domains. DPPBT-based copolymers, including different branched alkyl ester-labeled side chains, are spun-cast on polymer-treated SiO2 dielectrics from dilute chloroform solutions for organic thin-film transistors. A DPPBT-based copolymer with properly engineered side chains (i.e., 2-decyltetradecyl ester-labeled side chains) shows the highest hole mobility of 2.30 cm2 V-1 s-1 and an on/off current ratio of above 106.
Abstract Recently, perovskite solar cells (PSC) with high power‐conversion efficiency (PCE) and long‐term stability have been achieved by employing 2D perovskite layers on 3D perovskite light absorbers. However, in‐depth studies on the material and the interface between the two perovskite layers are still required to understand the role of the 2D perovskite in PSCs. Self‐crystallization of 2D perovskite is successfully induced by deposition of benzyl ammonium iodide (BnAI) on top of a 3D perovskite light absorber. The self‐crystallized 2D perovskite can perform a multifunctional role in facilitating hole transfer, owing to its random crystalline orientation and passivating traps in the 3D perovskite. The use of the multifunctional 2D perovskite (M2P) leads to improvement in PCE and long‐term stability of PSCs both with and without organic hole transporting material (HTM), 2,2′,7,7′‐tetrakis‐( N , N ‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) compared to the devices without the M2P.
Abstract Despite organic/inorganic lead halide perovskite solar cells becoming one of the most promising next‐generation photovoltaic materials, instability under heat and light soaking remains unsolved. In this work, a highly hydrophobic cation, perfluorobenzylammonium iodide (5FBzAI), is designed and a 2D perovskite with reinforced intermolecular interactions is engineered, providing improved passivation at the interface that reduces charge recombination and enhances cell stability compared with benchmark 2D systems. Motivated by the strong halogen bond interaction, (5FBzAI) 2 PbI 4 used as a capping layer aligns in in‐plane crystal orientation, inducing a reproducible increase of ≈60 mV in the V oc , a twofold improvement compared with its analogous monofluorinated phenylethylammonium iodide (PEAI) recently reported. This endows the system with high power conversion efficiency of 21.65% and extended operational stability after 1100 h of continuous illumination, outlining directions for future work.
Abstract Perovskite light-emitting diodes (PeLEDs) based on three-dimensional (3D) polycrystalline perovskites suffer from ion migration, which causes overshoot of luminance over time during operation and reduces its operational lifetime. Here, we demonstrate 3D/2D hybrid PeLEDs with extremely reduced luminance overshoot and 21 times longer operational lifetime than 3D PeLEDs. The luminance overshoot ratio of 3D/2D hybrid PeLED is only 7.4% which is greatly lower than that of 3D PeLED (150.4%). The 3D/2D hybrid perovskite is obtained by adding a small amount of neutral benzylamine to methylammonium lead bromide, which induces a proton transfer from methylammonium to benzylamine and enables crystallization of 2D perovskite without destroying the 3D phase. Benzylammonium in the perovskite lattice suppresses formation of deep-trap states and ion migration, thereby enhances both operating stability and luminous efficiency based on its retardation effect in reorientation.
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