Study On The Phase Microstructure And Properties Of The Conjugated/Insulating Polymer Blends

Insulators play important roles in improving the solubility, processability, environmental and electrical stability of the organic semiconductor materials. In this work, we systematically study the insulator/semiconductor blends and various factors which have impact on the phase separation, interface structure and the phase separation mechanism of the blend films. We also developed a method using the surface aggregation to induce the vertical phase separation, and research on the application of the vertical phase separation in organic field effect transistors. The results are as follows:1. Vertical phase separation and the application of the P3HT/PMMA blends.We have systematically investigated the film formation conditions, the polymer structures, physics properties and the substrate properties of the P3HT/PMMA blends solutions. The low surface energy induces the surface aggregation of the P3HT so that vertical phase separation happens in the blend films forming the bilayer structure with the P3HT on the top and the PMMA on the bottom. We have developed a one-step fabrication method of the semiconductor and insulator layers simultaneously. The mobility of the all polymer flexible devices reaches the highest values 0.012 cm2V-1S-1 and the on/off ratio is 2×105. The devices exhibit excellent charge transport properties.This technology is suitable for flexible substrate and can prepare flexible devices.2. The application in gas sensor of the P3HT ultrathin films.By using the surface aggregation of P3HT/PMMA blend films, we can control the film thickness of the P3HT films. The P3HT films can be prepared by reversing, transferring and selective dissolution of the blend films. When the ratio of the PMMA/P3HT blend is 10/1, 20/1, 40/1, 60/1 and 80/1, the thickness of the P3HT films is 7.4 nm, 5.2 nm,2.8 nm, 2.2 nm and 1.9 nm respectively. The relationship between the P3HT film thickness and charge transport performance and sensing properties was studied. It was found that the mobility decreased slightly with the decrease of P3HT film thickness, but the performance of ammonia sensor was improved rapidly. The sensitivity of the P3HT ultrathin film with 1.9 nm thickness is 31.9 %, and the response and recovery time is 8.19 s and 79.36 s, respectively.3. Design, synthesis of high performance conjugated D-A polymers and research on the D-A polymer/PMMA blend films.In consideration of the excellent stability and the electrical properties, we investigate on three PBIBDF polymers with different insulator group positions. Donor-acceptor polymers based on(3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo-[1,2-b:4,5-b0]-difuran-2,6(3H,7H)-dione(BIBDF) and three kinds of dialkylated bithiophenes with head-to-head (HH),head-to-tail(HT) and tail-to-tail(TT) were synthesized by stille coupling reaction. The impact of the insulator group positions on molecular energy level, stacking, orientation and morphology are investigated. Density functional theory (DFT) calculations indicate that the difference between the HOMO of the polymers is caused by the alkyl chains substituted near the BIBDF-thiophene connection show more steric hindrance than substitution near the thiophene-thiophene connection. The PBIBDF polymers exhibit excellent carrier transport properties with a maximum electron mobility of 1.23 cm2 V-1 s-1 and a maximum hole mobility of 0.37 cm2 V-1 s-1. The ultrathin PBIBDF-HH films can be prepared from the PBIBDF-HH/PMMA blend films. The morphology and the field effect transistors properties are investigated.