Long-Term Operations of Polymeric Thin-Film Transistors: Electric-Field-Induced Intrachain Order and Charge Transport Enhancements of Conjugated Poly(3-hexylthiophene)

Enhanced Functionality of Dual-Gate Organic Transistors Based on Semiconducting/Insulating Polyblend-Induced Asymmetric Charge Modulation Layers

Dual-gate organic thin-film transistors (DG-OTFTs) with enhanced functionality, including large current enhancement behavior, highly efficient threshold voltage controllability, and self-contained dual-mode logic gate features, are reported. These DG-OTFTs are based on a semiconducting/insulating polyblend-based active layer with asymmetric top and bottom charge modulation layers (atb-CMLs). The atb-CMLs are automatically generated through the preparation of multilayer stacks of phase-separated semiconducting poly(3-hexylthiophene) (P3HT):insulating poly(methylmethacrylate) (PMMA) polyblend layer, poly(vinylidene fluoride) (PVDF) layer, and cross-linked-poly(4-vinylphenol) (cPVP) layer. They consist of a thin PMMA bottom layer and an uneven-shaped PMMA:PVDF miscible mixture-based top layer. The presence of the polarizable insulating PMMA, PVDF, and PMMA:PVDF mixture regions causes the bottom and top CMLs to experience electrical polarization, which induces the dipole field to achieve efficient charge modulation functions in DG-OTFTs. Owing to the presence of atb-CMLs, the DG-OTFTs exhibit unprecedented electrical characteristics, such as the easy depletion of the bottom channel by the top gate potential. However, the top channel can work properly only when given a bottom gate potential (either positive or negative). Given these unusual electrical features, the design of the fundamental dual-mode logic gates (e.g., AND and OR gates) can be achieved with just one DG transistor. This finding opens an interesting direction for the preparation of DG-OTFTs with diverse operating modes and increasing functionality, thereby widening the application potential of such transistors.

Dynamic Evolution from Chain Disorder to Order of PTB7 Condensed State Structures under External Fields

In this research, the effect of external fields (solvent, temperature, solution concentration, and external force) on dynamic evolution from chain disorder to order of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b:4,5- b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b]thiophenediyl]] (PTB7) condensed state structures was explored by UV-vis absorption spectra, atomic force microscope, and transmission electron microscopy (TEM). It was found that PTB7 main chains presented amorphous conformations induced by the poor solvent 1,2-dichloroethane. However, the local ordered aggregation appeared in amorphous conformations when the solubility of the poor solvent was again lowered by reducing temperature. It is worth noting that the size of ordered aggregation was further increased with the decrease of solution concentration or increase of external force. It was found that there were two main PTB7 absorption peaks in the UV-vis absorption spectra; we denoted A_0 -0 for the intensity of the lower energy absorption peak and A_0-1 for the intensity of the higher energy absorption peak. The ratio R = A_0-0/ A_0-1 was used to characterize the dynamic evolution from disorder to order of the PTB7 condensed state structures in absorption spectra. It increased from 0.94 for PTB7 amorphous state to 1.25 for PTB7 large-size ordered aggregation. The dynamic evolution from chain disorder to order could also be distinctly observed by TEM. It was inferred that PTB7 condensed state structures (amorphous state, local ordered aggregation, and large-scale ordered aggregation) might exist simultaneously because of the complexity of copolymer conformations. This research is meaningful to establish physical basis for the molecule design and the synthesis of materials to enhance photoelectronic device efficiency based on condensed matter physics of conjugated polymer.

Synergistic Effects of Binary-Solvent Annealing for Efficient Polymer-Fullerene Bulk Heterojunction Solar Cells

Conjugated polymer-fullerene-based bulk-heterojunction (BHJ) organic solar cells (OSCs) have attracted tremendous attention over the past two decades because of their potential to develop low-cost and easy methods to produce energy from light. The complicated microstructure and morphology with randomly organized architecture of these polymer-fullerene-based active layers (ALs) is a key factor that limits photovoltaic performance. In this study, a binary-solvent annealing (BSA) approach was established to improve the poly(3-hexylthiophene):indene-C60 bisadduct-based AL for efficient BHJ-type OSCs by varying the second solvents with different boiling points (BP). Thus, we were able to change the evaporation behavior of cosolvents and consequently obtain the various microstructural properties of the AL. An in-depth study was conducted on the solvent-evaporation driven morphology of the active layer under various cosolvent conditions and its effect on the photovoltaic parameters of OSCs. Under the BSA processes, we found that the specimens with low-BP second solvents allows us to observe a more ideal AL for increasing photon absorption and efficient charge transport and collection at the respective electrodes, resulting in enhanced PCE of the corresponding OSCs. By contrast, the specimens with high-BP second solvents exhibit random microstructures, which are detrimental to charge transport and collection and lead to diminished PCE of the corresponding OSCs. By appropriately selecting the composition of a binary solvent, BSA can be employed as an easy method for the effective manipulation of the microstructures of ALs. BSA is a promising technique for the performance enhancement of not only OSCs but also other organic/polymeric-based electronic devices.

Spontaneous Formation of an Ideal-Like Field-Effect Channel for Decay-Free Polymeric Thin-Film Transistors by Multiple-Scale Phase Separation

We demonstrate semiconducting polymer-based thin-film transistors (PTFTs) with fast switching performance and an uncommon nondecaying feature. These PTFTs based on widely studied poly(3-hexylthiophene) are developed by incorporating the insulating polymer into the active channel and subjecting the compound to specific, spontaneous multiple-scale phase separation (MSPS). An in-depth study is conducted on the interfacial and phase-separated microstructure of the semiconducting/insulating blending active layer and its effect on the electrical characteristics of PTFTs. The polyblends exhibit a confined crystallization behavior with continuously semiconducting crystalline domains between scattered insulator-rich domains. The insulator-rich domains can block leakage current and strengthen the gate control of the channel. A small amount of the insulating polymer penetrates the bottom of the active channel, resulting in effective interface modification. We show specific MSPS morphology of the present blending films to reduce charge trapping effects, enhance charge accumulation, and create a high-seed switching channel. The findings enable us to develop the required morphological conceptual model of the ideal-like field-effect-modulated polymer-based active channel. The polyblend-based PTFTs with MSPS morphology also have promising sensing functions. This study offers an effective approach for overcoming the major drawbacks (instability and poor switching) of PTFTs, thus allowing such transistors to have potential applications.

Self-assembly of large-scale P3HT patterns by confined evaporation in the capillary tube

Large-scale P3HT stripe patterns based on a controlled evaporation self-assembly method in a capillary tube have been fabricated.