Improving Charge Carrier Mobility of Polymer Blend Field Effect Transistors with Majority Insulating Polymer Phase

Abstract

The key approach to achieve high performance field effect transistor fabricated from semiconducting/insulating polymer blends with majority insulating polymer phase is the formation of connected fibrous structures of semiconducting polymer and good interfacial interaction of semiconducting polymer with the dielectric layer. Herein, tetrahydrofuran (THF) as a marginal solvent was used as an additive in marginal/good solvent mixtures to control the crystallite structure, phase segregation, and hole transport properties of poly­(3-hexylthiophene)/poly­(styrene) (P3HT/PS; weight ratio: 1/4) blends, with the advantage that marginal/good solvent mixture gives P3HT sufficient time for phase segregation and relatively better solvent quality to aggregate to more stable structures compared to other reported strategies as bad/good solvent mixtures or directly marginal solvents. Incorporation of THF reduces the P3HT solubility, forming connected fibrous structures as observed in both neat P3HT and blend films; it appears these structures are responsible for improved charge transport. Furthermore, enhanced molecular ordering, π–π stacking and conjugation length are observed with increasing THF amount. THF promotes the edge-on orientation and more stable crystal structures in P3HT, while the lattice spacing remains the same. Finally, the added THF increases hole mobility for P3HT/PS blend FETs, reaching a maximum value of 4 0.0 × 10–3 cm2/(V s) with 20 vol % THF and being comparative to neat P3HT; however, THF has an insignificant influence on the hole mobility for neat P3HT FETs. Morphological characterization supports the idea that differential solubility creates both enhanced chain ordering and vertical phase segregation that both improve FET performance. These results are promising for the development of environmentally stable and lower cost polymer electronics.

Enhanced Hole Transport in Ternary Blend Polymer Solar Cells

“…Similar improvements have been reported for blends of a semiconducting polymer that is mixed with a high-bandgap polymer. [39][40][41] In these diluted blends, the charge transport was improved or comparable to that in neat films. Thus, such dilution would be versatile approach to improving charge transport.…”

“…As summarized in Table 2, the hole mobility in binary blend films was comparable to or larger than that in neat films. [39][40][41] In these diluted blends, the charge transport was improved or comparable to that in neat films. As shown in Figure 7, trap filling region was observed from 0.1 to 1 V for both PTB7-Th and PDCBT neat films but not observed for the ternary blend film.…”

“…[42,43] Such an improvement in ordering of polymer chains has been reported for a crystalline polymer P3HT blended with polystyrene. [41] We therefore conclude that the improvement in hole transport is due to higher ordering of PTB7-Th chains in ternary blend films.…”

Collapse Transition‐Assisted Crystallization in P3HT Solution

“…The film formed from the incubated cool solution at 16 °C shows pronounced nanofibrillar networks, suggesting a chain‐collapse‐assisted crystallization. Moreover, the nanofibrils display some ordered orientation locally, which is beneficial for improving the charge transport property . The surface roughness of the films is characterized by its root‐mean‐square roughness ( R rms ), which could be described as the density or the coverage of crystalline nanofibrils in the films .…”

Ternary Blend Polymer Solar Cells Based on Wide-bandgap Polymer PDCBT and Low-bandgap Polymer PTB7-Th

“…18,19 The other possible mechanism is ascribed to the improvement in the hole mobility of ternary blends due to reduced trap sites compared to that of the binary blends as reported previously. 20,21 In such case, there would be a balanced charge transport between the hole and electron, giving rise to suppress the non-geminate recombination, and consequently the increase in FF. Further studies in terms of photophysical properties are required for an in-depth understanding the charge recombination dynamics in this ternary blend system.…”