Search for: All records

Ultrasound acoustic waves are demonstrated to assemble poly-3-hexylthiophene (P3HT) chains into nanofibers after they are fully dissolved in what are commonly considered to be ‘good’ solvents. In the absence of ultrasound, the polymer remains fully dissolved and does not self-assemble for weeks. UV-vis spectroscopy, ultra-small angle X-ray scattering (USAXS) and small angle neutron scattering (SANS) are used to characterize the induced assembly process and to quantify the fraction of polymer that forms nanofibers. It is determined that the solvent type, insonation time, and aging periods are all important factors affecting the structure and final concentration of fibers. The effect of changing polymer regio-regularity, alkyl chain length, and side chain to thiophene ratio are also explored. High intensity focused ultrasound (HIFU) fields of variable intensity are utilized to reveal the physical mechanisms leading to nanofiber formation, which is strongly correlated to cavitation events in the solvent. This in situ HIFU cell, which is designed for simultaneous scattering analysis, is also used to probe for structural changes occurring over multiple length scales using USAXS and SANS. The proposed acoustic assembly mechanism suggests that, even when dispersed in ‘good’ solvents such as bromobenzene, dichlorobenzene and chloroform, P3HT chains are still not in a thermodynamically stable state. Instead, they are stabilized by local energy barriers that slow down and effectively prevent crystallization. Ultrasound fields are found to provide enough mechanical energy to overcome these barriers, triggering the formation of small crystalline nuclei that subsequently seed the growth of larger nanofibers. 

The nanoscale structure and macroscopic morphology of π-conjugated polymers are very important for their electronic application. While ordered single crystals of small molecules have been obtained via solution deposition, macroscopically aligned films of π-conjugated polymers deposited directly from solution have always required surface modification or complex pre-deposition processing of the solution. Here, ordered nanowires were obtained via shear-enhanced crystallization of π-conjugated polymers at the air–liquid–solid interface using simple deposition of the polymer solution onto an inclined substrate. The formation of macroscopically aligned nanowire arrays was found to be due to the synergy between intrinsic (π-conjugated backbone) and external (crystallization conditions) effects. The oriented nanowires showed remarkable improvement in the charge carrier mobility compared to spin-coated films as characterized in organic field-effect transistors (OFETs). Considering the simplicity and large-scale applicability, shear-enhanced crystallization of π-conjugated polymers provides a promising strategy to achieve high-performance polymer semiconductor films for electronics applications. 

All‐inorganic perovskite quantum dots (IPQDs) are a promising material for use in various optoelectronic devices due to their excellent optoelectronic properties and high environmental stability. Here, a high‐performance phototransistor based on a layered heterojunction composed of CsPbI₃QDs and a narrow‐bandgap conjugated polymer DPP‐DTT is reported, which shows a high responsivity of 110 A W⁻¹, a specific detectivity of 2.9 × 10¹³Jones and a light to dark current ratio up to 6 × 10³. The heterojunction phototransistor exhibits unipolar p‐type and gate bias modulated behaviors. In addition, the device exhibits a broad spectral detection range from ultraviolet to near infrared. The high sensitivity of the device is attributed to the layered heterojunction and the gate bias modulation property. The work overcomes the existing limitations in sensitivity of IPQD photodetectors due to the poor charge transport between QDs. The convenient solution‐processed fabrication and excellent device performance especially suggest the IPQD/narrow‐bandgap conjugate polymer heterojunction as a promising structure for potential applications of ultrasensitive broadband photodetectors compatible with a wide variety of substrates.