Planar-processed polymer transistors are proposed where the effective charge injection and the split unipolar charge transport are all on the top surface of the polymer film, showing ideal device characteristics with unparalleled performance. This technique provides a great solution to the problem of fabrication limitations, the ambiguous operating principle, and the performance improvements in practical applications of conjugated-polymer transistors.

A newly synthesized high-k polymeric insulator for use as gate dielectric layer for organic field-effect transistors (OFETs) obtained by grafting poly(methyl methacrylate) (PMMA) in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) via atom transfer radical polymerization transfer is reported. This material design concept intents to tune the electrical properties of the gate insulating layer (capacitance, leakage current, breakdown voltage, and operational stability) of the high-k fluorinated polymer dielectric without a large increase in operating voltage by incorporating an amorphous PMMA as an insulator. alt-5,5′-(2,2′-bithiophene)) are demonstrated here. DPPT-TT OFETs with P(VDF-TrFE)-g-PMMA gate dielectrics exhibit a reasonably high field-effect mobility of over 1 cm 2 V −1 s −1 with excellent operational stability. By controlling the grafted PMMA percentage, an optimized P(VDF-TrFE)-g-PMMA with 7 mol% grafted PMMA showing reasonably high capacitance (23-30 nF cm −2 ) with low voltage operation and negligible current hysteresis is achieved. High-performance low-voltage-operated top-gate/bottom-contact OFETs with widely used high mobility polymer semiconductors, poly[[2,5bis(2-octyldodecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo [3,4-c]pyrrole-1,4-diyl]alt-[[2,2′-(2,5-thiophene)bis-thieno(3,2-b)thiophene]-5,5′-diyl]] (DPPT-TT), and poly([N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-

Surface energy is a key factor in controlling the kinetics of nucleation and growth of perovskite, which are crucial for the formation of high quality films and the photovoltaic efficiency of solar cells. It has been reported that substrate wettability and perovskite grain size are to be compromised with necessity, as promoted heterogeneous nucleation that occurs on a hydrophilic surface reduces the grain size for a two-step deposition method. Herein, the increase in grain size on hydrophilic surfaces in the presence of hydroxyl groups and the direct correlation between the perovskite grain formation and photovoltaic performance are investigated. The surface energy of the hole transport layer in planar p−i−n type perovskite solar cells is modulated by the introduction of polymer surfactant additive, poly(ethylene glycol) tridecyl ether (PTE). Perovskite films deposited on a hydrophilic surface by a two-step method contain small grain size, leading to a reduction in photovoltaic performance. In contrast, surface hydroxyl groups were found to induce the preferential (110) orientation and large grain size in the perovskite films deposited by means of a one-step method. Nucleation and growth mechanisms are proposed to explain those different behaviors of the dependence of grain size on surface energy. The enlarged perovskite grains on hydrophilic surfaces lead to an efficiency improvement owing to an increase in the short-circuit current and fill factor. Our study highlights that the grain size increase and high crystallinity can be achieved even with accelerated heterogeneous nucleation on a hydrophilic substrate surface.

Despite the increasing understanding of charge transport in organic field-effect transistors (OFETs), charge injection from source/drain electrodes into organic semiconductors remains crucial for improving device performance and lowering power consumption. The analysis of contact resistance is generally carried out without clearly distinguishing the Schottky barrier and access resistance. Here we show that the access resistance through the organic semiconductor bulk can significantly influence the Schottky barrier evaluation and affect the charge-transport exploration. Indeed, access resistance plays a leading role in the contact resistance, whereas the Schottky barrier (expressed as the interface resistance) determines the charge injection at the metal/semiconductor interface. The Schottky barrier evaluation strongly depends on the access resistance and bias voltage. After eliminating the access resistance effect, the intrinsic Schottky barrier appears to be very coincident and weakly dependent on the work function of the contact metal. This work provides clues to understanding the Schottky barrier and charge injection in OFETs to optimize OFETs for high-performance and advanced applications.

The facile sequential deposition of functional organic thin films by solution processes is critical for the development of a variety of high-performance organic devices without restriction in terms of materials and processes. Herein, we propose a simple fabrication process that entails stacking multiple layers of functional polymers to fabricate organic field-effect transistors (OFETs). The process involves stamping organic semiconducting layers formed on the surface of water onto a commonly used polymeric dielectric layer. Our scheme makes it possible to independently optimize organic semiconductor films by controlling the solvent evaporation time during the process of film formation on the surface of water. This approach eliminates the need to be concerned about any interference with adjacent layers. Utilizing this process, the fabrication of high-performance bottom-gated OFETs is demonstrated on a glass and a flexible substrate. The OFETs consist of a vertically stacked diketopyrrolopyrrole-based polymer semiconducting layer on the poly­(methyl methacrylate) film with a maximum hole mobility of 0.85 cm2/V s.