UV-Vis absorption spectra of DCM-Q-BDT and DCV-B-BDT in chloroform solution (a) and as a thin solid film spin-cast from chloroform (b) Cyclic voltammograms of DCM-Q-BDT and DCV-B-BDT in dichloromethane solution (c) DFT calculation for DCM-Q-BDT and DCV-B-BDT (d). Electrical characteristics of DCM-Q-BDT and DCV-B-BDT OFETs depending on the post-annealing temperature.
Introduction
General Conjugated Conducting Materials: A Brief Overview
- The History of Conducting Materials
- The Electromagnetic Theory for Conducting Polymer (CPs)
- Conjugated Materials Synthesis: Methods and Reactions
- Chemical and Electronical polymerization
- Palladium (Pd) Catalyzed Cross Coupling Reaction
- Knoevenagel Condensation for Conjugated Small Molecules
- Electronic Applications
- Organic Photovoltaics (OPVs)
- Organic Field-Effect Transistors (OFETs)
- Reference
Depending on a number of layers and coated priority, OPV devices have different architectures, as shown in Figure 1.10. Moreover, the unique OPV system, such as bulk heterojunction, consisting of a mixture of electron donor and acceptor, have been developed to increase the efficiency of solar cells, as shown in Figure 1.11c.38.
Synthesis of Characterization of Benzodipyrrolidone (BDP)-Based Polymers
BDP-Based Polymers
- Introduction
- Synthesis and Characterization
- Photophysical and Electrochemical Properties and Computational Studies
- Thin Film Microstructure Analyses
- OFETs Performance
- Conclusions
- Experimental Section
- Reference
The optical properties of the polymers were analyzed and are shown in Figure 2.3, and detailed values are listed in Table 2.1. It is worth noting that PBDP-Se has an increased ICT band absorption intensity relative to the intensity of the -* transition compared to the intensity ratios of the two peaks for PBDP-Fu and PBDP-Th. This means that the electron donating ability of the donor chromophores increases in the order Fu < Th < Se.
To gain insight into the structural and electronic properties of the polymers, distributions of the HOMO and LUMO of PBDP-Fu, PBDP-Th and PBDP-Se were calculated using the DFT method at the B3LYP/6-31G* level and are shown in Figure 2.4 . Summary of the electrical properties of PBDP-Fu, PBDP-Th and PBDP-Se OFETs annealed at different temperatures.a. Thereby, our reliance on both PBDP-Th and PBDP-Se as relatively higher performance polymers is justified by the goal of systemically investigating the actual influence of the chalcogen atoms on intrinsic semiconducting properties.
Synthesis and Characterization of Conjugated Benzoditiophene-Based
BDT-Based Polymers
- Introduction
- Design, Synthesis, and Characterization
- Optical and Electrochemical Properties
- Computational Studies
- Solar Cell Performance and Film Morphology
- Conclusions
- Experimental Section
- Reference
The synthesis of the target monomers and polymers (PBDTTPD-C1, PBDTTPD-C3 and PBDTTPD-C4) are shown in Scheme 3.1 and the detailed synthetic procedures are given in the experimental section. Cyclic voltammetry (CV) was used to investigate the frontier orbital energy levels (HOMO and LUMO) of BDT-based polymers (Figure 3.2c). To achieve such ideal n-type OSCs, a high electron affinity (i.e., lowest unoccupied molecular orbital [LUMO]) as well as a large intermolecular orbital overlap via strong - stacking are extremely necessary to lighten the load. injection and transport with a strong stability in air.8 The inclusion of electron substituents in the conjugated cores enables the lowering of the LUMO energy levels so that the electron charge carriers are less sensitive to H2O and O2, 9, 10 which has been proven to be a facile and effective approach for air-stable n-type OSCs.
The large discrepancy between the LUMO energy level and the work function of the Au electrode (4.6 ~ 5). The half-life of the drain current was approximately 35 hours for the DCM-Q-BDT OFETs and 1 hour for DCV-B-BDT. The conventional FET and the corresponding VTh were extracted in the saturation region using gradual channel approximation equations for a standard metal oxide semiconductor FET (MOSFET). The source drain electrode contact resistance (Rc) of the individual transistors is calculated in the liner region (at Vd= 10V, Vg= ~80V) by the Y-function method and also the extracted Rc was normalized using channel width (Rc∙W).
Solution Processable TIPS-Benzodithiophene Based Small Molecules for n-
Introduction
Solution-processable organic semiconductors (OSCs) have been extensively researched due to their unique optoelectronic properties and excellent mechanical flexibility for wearable electronics. Even though there are some successful examples of n-type organic semiconductors (OSCs), such as fullerene and arylenediimide derivatives, 5-7 progress in the field of n-type OSCs has generally lagged behind the development of p-type OSCs. due to the relative difficulty of obtaining n-type OSCs with good processability, air stability and high electrical performance. Linearly fused benzo [1,2-b:4,5-b'] dithiophene (BDT) with a centrosymmetric structure is known to have a strong tendency to -stack in the solid state.25 Although this rather unique property has recently been exploited for the demonstration of a number of high-performance OSCs in community solar cells, 26,27 its applications as OFET OSCs have rarely been studied.
Along with the goal of obtaining a quantitative understanding of OSCs nature using each type of terminus mentioned above, our ongoing interest in the chemistry of BDT and the development of high-performance n-type OSCs prompted us to synthesis and properties of BDTs capped with dicyanomethylene and dicyanovinyl groups, respectively (DCM-Q-BDT and DCV-B-BDT, Scheme 4.1), where bulky triisopropylsilylacetylene (TIPS) side chains on the central phenyl ring of the BDT unit is introduced in order to simultaneously improve the solubility, oxidative stability and -orbital overlap of the OSCs. The solution-processed top gate/bottom contact (TG/BC) OFETs of DCM-Q-BDT without post-thermal treatment show high electron mobility up to 0.23 cm2/V.s. Furthermore, the OFETs using DCM-Q-BDT have excellent long-term air-stable n-channel characteristics; DCM-Q-BDT has longer half-life times of 35 hours than that of DCV-B-BDT by one order of magnitude.
Synthesis and Characterization
Optical and Electrochemical Properties and DFT Calculation
Both DCM-Q-BDT and DCV-B-BDT exhibited red-shifted and broadened absorptions in the films compared to those in the solutions. It is interesting to note that despite the extended -conjugation length of the dicyanovinyl unit over dicyanomethylene, the optical band gap estimated from the absorption onset of the DCM-Q-BDT film was found to be 1.67 eV is, which is 0.38 eV smaller than this. of DCV-B-BDT (Egopt = 2.05 eV), as a reflection of the quinoid character along the core of DCM-Q-BDT.28, 29. As shown in Figure 4.2c, DCM-Q-BDT has two reversible reduction given waves, while DCV-B-BDT exhibited three quasi-reversible reduction waves; the first onset potential was 0.64 V for DCM-Q-BDT and 0.75 V for DCV-B-BDT, but no oxidation waves were available in the potential range.
The LUMO energies of DCM-Q-BDT and DCV-B-BDT estimated via the equation ELUMO= -(E(red)onset – E(ferrocene)onset + 4.8) eV were 4.12 and 4.01, respectively eV, both of which are 4.0 eV below the vacuum level, well within the requirement for useful n-type OFET OSCs.30,31 Note that the relative lower LUMO level of DCM-Q-BDT clearly indicates that the quinoid structure contributes. to an increase in the electron level. -deficient nature compared to the benzenoid system. Interestingly, the HOMO of DCM-Q-BDT and LUMO of DCM-B-BDT show a similar orbital distribution, inversely.
Evaluation of OFET Device Properties
OFET top/bottom contact structure and transmission and output curves of DCM-Q-BDT (a), (b) and DCV-B-BDT OFET (c), (d) without post-annealing treatments. In the transistor output curves (Figure 4.3), the DCM-Q-BDT OFETs showed a fairly good contact property with the Au electrode, while the DCV-B-BDT OFETs showed a large sublinearity of the output characteristics at low VDS corresponding to high Rc based on the Schottky barrier. The stability in air without DCM-Q-BDT and DCV-B-BDT OFETs after annealing was tested using measuring devices in air (60% humidity and 25 oC).
As shown in Figure 4.5, DCM-Q-BDT OFETs showed quite good and much better air stability than DCV-B-BDT. Output curves at low VDS of OFETs with extracted contact resistance by YFM with DCM-Q-BDT (a) and DCV-B-BDT (b), Schematic energy diagram between OFETs electrode and organic semiconductors for carrier injection DCM-Q-BDT and DCV-B- BDT(c). Normalized Ids change of DCM-Q-BDT and DCV-B-BDT OFETs according to time in air for ambient (60% humidity and 25 oC) stability.
Thin-film Microstructure and Morphology
The stability of n-type OFETs is known to be relatively worse than their p-type counterpart, as many trap sites are created at around -3.8 eV by exposure to air (moist oxygen).9,38,39 Energetically, the LUMO energy levels of n-type OSCs should be designed below -4.0 eV for air stability. In addition, the molecular packing and thin film morphology of n-type OSC films play important roles in the air stability of n-type OFETs. Kinetically, dense molecular packing, good film morphology with high crystallinity, and low density of grain boundaries with large grain sizes are positive kinetic factors for the realization of air-stable n-type OFETs.40,41 The high air and functional stability of DCM-Q-BDT is based not only on the relatively lower LUMO energy level (-4.12 eV) compared to DCV-B-BDT (-4.01 eV), but also on better film morphology and crystallinity of DCM-Q-BDT than DCV-Ato B-BDT (discussed below).
This indicates that the benzenoid structure had a relatively denser lamellar packing compared to the quinoid analogue, although higher mobilities were observed in the DCM-Q-BDT film (vide supra). Unlike the diffraction patterns of conventional OSCs, however, there were almost no (010) diffraction peaks in both qz and qxy directions for all thin films. DCV-B-BDT films had arcs for the qz direction, suggesting oriented film with wide orientation distribution, while for DCM-Q-BDT, pronounced ellipses were produced, which is evidence of well-aligned crystallite with a only similar. feature.
Conclusion
Experimental Section
비록 쉽지 않은 시간이었지만, 박사 학위를 취득하기로 결정한 순간부터 끝까지 부족하지 않게 기억하는 것은 배움에 대한 후회와 노력이 부족하다는 불평입니다. 먼저, 연구자로서 생명지표를 가르쳐주시고 아낌없는 지원을 해주신 지도교수님 양창덕 교수님께 깊은 감사의 말씀을 전하고 싶습니다. 아직은 부족하지만, 학위과정에서 교수님으로부터 배운 다양한 경험과 연구를 바탕으로 앞으로도 연구자로서 더욱 열심히 노력하겠습니다.
그들의 공동연구 덕분에 나의 실험은 더욱 빛을 발했다. 이 기회를 빌어 진심으로 감사의 말씀을 전하며 좋은 모습으로 다시 뵙기를 바랍니다. 또한 제가 연구자로 활동하는 동안 많은 조언을 해주신 경상대학교 이종진 교수님, 좁은 분야에서 많은 조언을 해주신 대구대학교 이성호 교수님에게도 감사의 말씀을 전하고 싶습니다. 앞으로도 최선을 다해 좋은 모습 보여드릴 수 있도록 노력하겠습니다.
Acknowledgement (English version )
