Semiconducting Organosilicon-based Hybrids for the Next Generation of Stretchable Electronics

During past years, organic-based electronic devices revealed high promise to supplement the ubiquitous silicon-based electronic devices and enable new fields of applications. At the center of this development is the considerable progress regarding π-conjugated polymer semiconductors (PSCs): Due to their processability from solution, light-weight, as well as low-cost, PSCs are now evolving towards production-scale of new technologies, e.g., in organic solar cells (OSCs), organic field-effect transistors (OFETs), and organic light emitting diodes (OLEDs). Especially OFETs are of fundamental importance, as they constitute the switching units in all logic circuits and display technologies. However, the future world is expected to be full with smart electronics and communication devices integrated in clothes, tools and even interacting with the human body, e.g., as on-skin wearable sensors. For this the electrically-active material, just as a human tissue, requires to combine several properties in addition to being charge conducting: They need to show (i) mechanical softness, (ii) capacity to repair, (iii) multimodal sensitivity, as well as (iv) biodegradability. Here, PSCs still face challenges as they are brittle and break upon applying a mechanical stress. When trying to address this issue, the existing knowledge on mechanical properties of well-established polymeric plastics, e.g., polystyrene, cannot be directly applied for several reasons, e.g., (i) the bulkiness of monomers (including long side-chains), (ii) the rigid π-conjugated backbone, (iii) the low degree of polymerization, (iv) the small quantities in which PSCs are available, etc. Moreover, these kinds of materials should not only be mechanically compliant and stretchable, but furthermore retain their charge mobility upon stretching, and withstand numerous of mechanical stretching cycles. Considering this complex problem, researchers have been developing and investigating several approaches to combine good electrical properties and mechanical compliance within one material. These approaches include (i) stress-accommodating engineering, (ii) blending of PSCs into elastic matrix, as well as (iii) molecular engineering approach. The latter seeks to interlink mechanical and electrical properties on the molecular level, i.e., synthesize polymers that are charge conducting and stretchable. Different strategies were tested, from the modification of side chains, to the introduction of conjugation breakings spacers into the backbone. Selected works sought to incorporate stretchability and conductivity by utilizing block copolymers, i.e., covalently linking a conjugated and a non-conjugated polymer chain, resulting in a phase separation of both constituents and preserving their respective properties. The ultimate goal of this work is to achieve an intrinsically stretchable and electrically high-performing PSC via the block copolymer approach. This is done by connecting organosilicone, namely the polydimethylsiloxane (PDMS) elastomer – possessing outstanding mechanical properties, as well as good environmental and air stability – with a conjugated diketopyrrolopyrrole (DPP)-based donor-acceptor copolymer. The final obtained structure of this polymer is a tri-block copolymer (TBC) consisting of an inner DPP-based polymer block and two outer soft PDMS polymer blocks. The content of PDMS block can be controlled and be very high (up to 67 wt%), and easy processing, e.g., via shear coating, is possible. Relatively high charge carrier mobilities – in the same range as the reference DPP-based copolymer (i.e., without outer PDMS blocks) – are retained, and the block copolymers withstands numerous stretching cycles (up to 1500 cycles) without losing electrical functionality. Finally, one of the block copolymers was successfully incorporated into a biosensor for COVID-19 antibodies and antigens detection. Overall, the findings of this work show that the block copolymer is a highly versatile approach to obtain functional and stretchable semiconductors with high charge carrier mobilities. Block copolymers consisting of a high-performing donor-acceptor PSC and a biocompatible elastomer could contribute towards one of the long-term goals of organic electronics – the realization of mechanically compliant materials for applications in stretchable electronics (e.g., wearable sensors, electronic skin, etc.)

Room-temperature bandlike transport and Hall effect in a high-mobility ambipolar polymer

The advent of new-class of high-mobility semiconducting polymers opens up a window to address fundamental issues in electrical transport mechanism such as hopping between localized states versus extended state conduction. Here, we investigate the origin of ultra-low degree of disorder (~ 16 meV) and band-like negative temperature (T) coefficient of the field effect electron mobility in a high performance diketopyrrolopyrrole (DPP)-based semiconducting polymer. Models based on the framework of mobility edge (ME) with exponential density of states are invoked to explain the trends in transport. The temperature window over which the system demonstrates de-localized transport was tuned by a systematic introduction of disorder at the transport interface. Additionally, the Hall mobility extracted from Hall-voltage measurements in these devices was found to be comparable to field effect mobility in the high T band-like regime. Comprehensive studies with different combinations of dielectrics and semiconductors demonstrate the effectiveness of rationale molecular design which emphasizes uniform-energetic landscape and low re-organization energy

Very large π-conjugation despite strong nonplanarity : a path for designing new semiconducting polymers

When two π-conjugated fragments are connected by a bond between two sp2 carbon atoms, a torsion around this bond is expected to break the overall π-conjugation. We show that for specially selected monomers, the π-conjugation is insensitive to torsions around a C–C bond up to about 60°. We provide a number of examples for this very unexpected phenomenon and a simple explanation. We propose that this feature can be incorporated into conjugated polymers to generate semiconducting materials that are extremely insensitive to structural disorder

Development of Organic Semiconductors for Soft Electronics

Organic semiconductors, Soft electronics, Colloid, Mini-emulsion synthesis, Breath-figure moldingOrganic semiconductor based soft electronic devices are demonstrated: (1) effects of conjugation length on charge transport in polymer semiconductors, (2) water-borne colloids of organic semiconductors, and (3) breath-figure molding of polymer semiconductors for sensors. To improve the charge carrier mobility of diketopyrrolopyrrole donor-acceptor copolymer semiconductors, the length of the donor building block is controlled using vinylene moieties, and its effects on crystalline structure and charge transport are systematically studied. We synthesize P29-DPP-TBT with two vinylene linkages between thiophene units and compare it with P29-DPP-TVT with single vinylene linkage. Density functional theory calculations predict enhanced backbone planarity of P29-DPP-TBT compared to P29-DPP-TVT, which can be related with the increased conjugation length of P29-DPP-TBT as proved by the increased free exciton bandwidth extracted from UV-vis absorption spectra and the wavenumber shift of the C–C peaks to higher values in Raman spectra. From two-dimensional grazing incident X-ray diffraction studies, it is turned out that the paracrystalline disorder is lower in P29-DPP-TBT than in P29-DPP-TVT. Near-edge X-ray absorption fine structure spectroscopy reveal that more edge-on structure of polymer backbone is formed in the case of P29-DPP-TBT. By measuring the temperature-dependence of the charge carrier mobilities, it is turned out that the activation energy for charge hopping is lower for P29-DPP-TBT than for P29-DPP-TVT. Collectively, these results imply that the substitution of extended π-conjugated donor moiety of polymeric semiconductors can yield a more planar backbone structure and thus enhanced intermolecular interaction which enables more perfect crystalline structure as well as enhanced charge transport behavior. A synthetic approach has demonstrated to enhance coalescence phenomenon during solidification of water-borne colloids so that thin, even, and continuous film morphology of polymer semiconductors can be realized. From theoretical study of complex colloids, it is shown that small-sized and uniform colloid particles are essential to minimize depletion contact energy between colloid particles and thus to enhance coalescence. Therefore, the newly synthesized polymer semiconductor is designed for better molecular affinity with surfactants, so that phase transfer of polymer semiconductors from organic phase to water phase can proceed more efficiently during mini-emulsion synthesis. This is achieved by substituting a Si atom to the branching C atom of the alkyl solubilizing group of a conventional donor-acceptor polymer semiconductor. Such a chemical modification increases the volumetric portion of hydrophobic alkyl chains and thus enables higher solu-bility as well as higher hydrophobicity, all of which are closely related with enhancing molecular affinity be-tween polymer semiconductor and surfactants. As a result, the performance of organic field-effect transistors fabricated from water-borne colloids can be improved to a level similar to the case of organic solvents. More importantly, the reproducibility of transistor performance is also greatly improved due to the small and uni-form water-borne colloidal particles. Strategically designed polymer semiconductor thin film morphology with both high responsivity to the specific gas analyte and high signal transport efficiency is reported to realize high-performance flexible NOx gas sensors. Breath-Figure (BF) molding of polymer semiconductors enables a finely defined degree of nano-porosity in polymer films with high reproducibility while maintaining a high charge carrier mobility characteristics of organic field effect transistors (OFETs). The optimized BF-OFET with a donor-acceptor copolymer exhibits a maximum responsivity of over 104%, sensitivity of 774%/ppm, and limit of detection (LOD) of 110 ppb against NO. When tested across at NO concentrations of 0.2–10 ppm, the BF-OFET gas sensor ex-hibits a response time of 100–300 s, which is suitable for safety purposes in practical applications. Further-more, BF-OFETs show a high reproducibility as confirmed by statistical analysis on 64 independently fabri-cated devices. Selectivity to NOx analytes is tested by comparing the sensing ability of BF-OFET to other re-ducing gases and volatile organic compounds. Finally, flexible BF-OFETs conjugated with plastic substrates are demonstrated and they exhibit a sensitivity of 500%/ppm and LOD of 215 ppb, with a responsivity degradation of only 14.2% after 10,000 bending cycle at 1% strain.YPart Ⅰ. Effects of conjugation length on crystalline perfectness and charge transport in diketopyrrolopyrrole-based polymer semiconductors 1 Ⅰ. Introduction 2 Ⅱ. Experimental Section 3 2.1 Materials 3 2.2 Device fabrication 3 2.3 Characterization 4 2.4 Measurements 4 Ⅲ. Results and Discussions 5 Ⅳ. Conclusion 13 Ⅴ. References 14 Part Ⅱ. Facilitating Phase Transfer of Polymer Semiconductor in Mini-Emulsion Synthesis via Molecular Affinity Engineering 18 Ⅰ. Introduction 19 Ⅱ. Experimental Section 21 2.1 Materials 21 2.2 Colloid synthesis 21 2.3 Device fabrication 21 2.4 Characterization 21 2.5 Measurements 22 Ⅲ. Results and Discussions 22 3.1 Efficiency of Mini-emulsion 22 3.2 Film Morphology 26 3.3 Crystallinity and Molecular Orientation 28 3.3 Electrical Properties of Organic Field-effect Transistors (OFETs) 30 Ⅳ. Conclusion 32 Ⅴ. References 33 Part Ⅲ. Breath-Figure Molding of Polymer Transistors to Implement Flexible and High-Performance NOx Sensors 36 Ⅰ. Introduction 37 Ⅱ. Experimental Section 39 2.1 Device fabrication 39 2.2 Film characterization 39 2.3 Measurements 40 Ⅲ. Results and Discussions 40 Ⅳ. Conclusion 50 Ⅴ. References 51 국문요약 55본 논문은 유기 반도체를 이용한 유연 소자 개발 방법들을 제시한다: (1) 고분자 반도체의 공액 길이에 따른 전하 이동 영향, (2) 수분산 유기 반도체 콜로이드 합성 및 이를 이용한 소자 개발, (3) breath-figure 패턴 몰딩법을 이용한 센서 개발. 디케토피롤로피롤(diketopyrrolopyrrole) 전자 주개-받개 구조의 공중합체 반도체의 전하 운반체 이동성을 향상시키기 위해, 주개 구조의 길이는 비닐렌 단위체를 사용하여 제어된 채 결정 구조 및 전하 수송에 미치는 영향을 체계적으로 연구한다. 티오펜 단위체 사이에 2 개의 비닐렌 결합을 갖는 P29-DPP-TBT를 합성하고 단일 비닐렌 결합을 갖는 P29-DPP-TVT와 비교한다. 분자 이론 계산을 통하여 P29-DPP-TVT와 비교하여 P29-DPP-TBT의 향상된 백본 평면성을 예측하고, 자외선-가시광선 흡광 스펙트럼과 라만 스펙트럼을 이용하여 추출된 자유 엑시톤 대역폭이 증가함에 따라 P29-DPP-TBT의 공액 길이가 길어짐을 증명한다. 2 차원 X- 선 회절 분석법을 이용하여, P29-DPP-TVT보다 P29-DPP-TBT에서 결정성이 뛰어남을 확인하였다. 추가적으로, X- 선 흡수 미세 구조 분광법에서 P29-DPP-TBT의 경우에 고분자 백본이 더 많은 에지-온 구조로 형성됨을 보여준다. 전하이동도의 온도 의존성을 측정함으로써, 전하 호핑을 위한 활성화 에너지는 P29-DPP-TVT보다 P29-DPP-TBT에 대해 더 낮은 것으로 밝혀졌다. 종합적으로, 이들 결과는 공중합체 고분자 반도체의 연장된 π- 공액 전자 주개 부분의 치환이 보다 평면적 인 골격 구조를 생성할 수 있고, 이에 따라 보다 완전한 결정질 구조 및 향상된 전하 수송 거동을 가능하게 하여 분자간 상호 작용을 향상시킬 수 있음을 의미한다. 고분자 합성 측면에 있어 수성 콜로이드의 박막화 동안 응축 현상을 향상시켜서, 고분자 반도체의 얇고 균일하며 연속적인 박막 형태가 실현될 수 있음을 입증하였다. 콜로이드에 대한 이론적 연구로, 크기가 작고 균일한 콜로이드 입자가 콜로이드 입자 사이의 공핍 접촉 에너지를 최소화하고 따라서 응축을 향상시키는 데 필수적이라는 것이 밝혀졌다. 따라서, 새롭게 합성된 공중합체 고분자 반도체는 계면활성제와의 분자 친화성이 향상되도록 설계되어, 유기상으로부터 수상으로 공중합체 고분자 반도체의 상 전이가 미니-에멀젼 합성 동안 보다 효율적으로 진행될 수 있다. 이는 통상적인 전자 주개-받개 구조의 공중합체 고분자 반도체의 알킬 체인 그룹의 분 지형 C 원자에 Si 원자를 치환함으로써 가능하게 하였다. 이러한 화학적 변형은 소수성 알킬 체인의 부피를 증가시키고 따라서 더 높은 용해도 및 더 높은 소수성을 가능하게 하며, 이는 모두 공중합체 고분자 반도체와 계면활성제 사이의 분자 친화도를 향상시키는 것과 밀접한 관련이 있다. 결과적으로, 수계 콜로이드로 제조된 유기 전계 효과 트랜지스터의 성능은 유기 용매의 경우와 유사한 수준으로 개선될 수 있음을 입증하였다. 더불어 작고 균일한 수성 콜로이드 입자로 인해 박막 트랜지스터 성능의 재현성이 크게 향상된다. 특정 가스 분석 물질에 대한 높은 반응성과 높은 신호 전송 효율을 모두 갖춘 고분자 반도체 박막 모폴로지를 구현함으로써, 고성능의 유연한 NOx 가스 센서를 실현하였다. 고분자 반도체의 Breath-Figure (BF) 몰딩은 유기 전계 효과 트랜지스터 (OFET)의 높은 전하 캐리어 이동 특성을 유지하면서 고분자 박막에서 미세한 크기의 나노 다공성 표면 개질을 가능하게 하였다. 전자 주개-받개 구조의 공중합체 기반의 최적화된 BF-OFET는 최대 104 % 이상의 반응성과, 774% / ppm의 감도 및 NO에 대한 110 ppb의 검출 한계 (LOD)를 나타낸다. 0.2 ~ 10ppm의 NO 농도에서 측정시에 BF-OFET 가스 센서는 100 ~ 300 초의 응답 시간을 나타내며 이는 실제 응용 소자로 쓰일 수 있는 수준이다. 또한, BF-OFET는 64 개의 독립적으로 제조된 소자에 대한 통계 분석에 의해 확인 된 바와 같이 높은 재현성을 나타낸다. NOx 가스에 대한 선택성은 BF-OFET의 감지 능력을 다른 환원 가스 및 휘발성 유기 화합물과 비교하여 측정하였다. 최종적으로 플라스틱 기판과 접합된 유연한 BF-OFET을 구현하였으며 이 소자는 1% 변형률에서 10,000 회 굽힘 주기 후 14.2%의 응답성 저하를 보였으며, 500 % / ppm의 감도와 215ppb의 LOD를 나타냈다.MasterdCollectio

Synthesis and characterization of novel organic semiconducting materials for organic field effect transistors (OFETs) and photovoltaics (OPVs)

No abstract available.No abstract available

A Bottom-up Computational Approach to Semiconducting Block Copolymers

Conjugated polymers are very attractive materials for the scientists and industry due to low cost of the organic compounds, their lightweight, easy large-area processing from solution at low temperature and mechanical flexibility. Moreover, these materials are multifunctional and advanced technologies require both simultaneous n- and p-type conductance, i.e. ambipolarity. However, there are some hindrances which do not allow the wide spreading of this new generation of semiconductors into the market, first of all, due to their instability to ambient conditions. Moreover, determination of the tunable parameters which are responsible for high efficiency and controlled crystal packing ordering of the devices is rather complicated. A lot of efforts are done in order to improve the performance of the organic electronics as well as to shed light on the relation between the chemical structure and their intrinsic properties. Additionally, the governing factors which define the conductive properties of these materials are still under debate and this remains a great challenge for the researchers. One way to gain insight into the characteristics of polymeric materials is to begin exploring the polymers from their small constitutive units and then step-by-step to construct and characterize every compound up to macromolecular level. In this work, the semiconducting block copolymers, as promising candidates for application in organic transistors, are investigated starting from their small donor and acceptor blocks up to monomers and macromolecules, using computational methods running on different time and length scales. It is found out that the charge transport depends on the symmetry of molecules and the hopping mobilities can be predicted from isolated stacks of dimers, which are defined by minimum energy, without knowledge of the actual crystal structure. Interestingly, the polymers moieties prefer to build up mixed stacks and the flanks form segregated columns if there are no present defects in the samples. At each step of the investigation the results are compared with available experimental data

Investigation of Low Optical-Gap Donor and Acceptor Materials for Organic Solar Cells

Development of efficient and clean energy sources to meet the ever-increasing de- mand of humankind is one of the greatest challenges of the 21st century. There is a dire need to decarbonise the power sector, and the focus needs to shift to re- newable resources such as wind and solar energy. In this regard, organic solar cells are a promising and novel technology owing to its low carbon footprint, innovative applications, and possible integration into the current infrastructure. Due to its unique advantages, a considerable research effort has been put into its development in the last decades. As a result, the power conversion efficiency (PCE) of the organic photovoltaics has steadily risen from as low as 0.5% to around 17 % at the current stage. This improvement primarily originates from the better understanding of the underlying physical processes and as a result of extensive material development. In the most general case, organic solar cells consist of a binary blend of an electron donating and an electron accepting organic semiconductor forming the so-called ‘bulk-heterojunction’ (BHJ) morphology. Thermodynamics places an upper limit on the power conversion efficiency (PCE) of binary blend BHJ devices and for further enhancement in efficiency novel device concepts like the use of ternary blends and tandem device architectures is being investigated. In relation to these approaches, the development of low optical-gap (Eopt ≤ 1.5 eV) organic semiconductors has gained importance as these materials provide for the complementary absorption with respect to the other components and better harvesting of the solar spectrum. This work mainly deals with the investigation of low optical gap donor and acceptor materials for organic solar cells. We investigate the effect of the molecular structure on the device performance and the photophysical processes in the binary and ternary blend configuration. In the first part of the thesis, we study a family of low optical- gap diketopyrrolopyrrole (DPP) based polymers while varying the conjugated core and the branching position and length of the solubilizing alkyl side chains. The branching position of the side chains is found to have a significant influence on the polymers ability to crystallize, which in turn influences the mobility of free charge carriers. The branching position also affects the solubility of the polymer, which in turn influences the morphology of the bulk-heterojunction (BHJ) and ultimately the yield of photogenerated charge carriers. To investigate the electron transfer and charge separation dynamics in the blends consisting of DPP polymers and fullerene, we employed ultrafast pump-probe spec- troscopic techniques. In the spectroscopy data, we observe signatures suggesting an ultrafast electron transfer process and an efficient charge separation process due to the high mobility of the free charge carriers shortly after separation (∼10-100 ps). Lastly, we investigated indacenodithiophene (IDT) based non-fullerene acceptor (NFA) molecules. In particular, we studied the effect of fluorination on the device performance when these acceptors are blended with PTB7-Th and P3HT donor polymers. The kinetics of the photophysical processes in the binary and ternary blends are characterized using ultrafast spectroscopy and related to the morphology of the blend and the molecular structure of the acceptors. Overall, we investigated the structural variations in the DPP polymers and flu- orinated non-fullerene acceptor (NFA) molecules and suggest design rules for the synthesis of optimal DPP polymers and non-fullerene acceptors to achieve supe- rior device performance. Additionally, we also shed light on the phenomenological processes happening on an ultrafast time scale (0.2-1000 ps) in the binary and the ternary blends with the aim of developing a better understanding of the photophys- ical processes in these promising material systems

Parallel triplet formation pathways in a singlet fission material

Harvesting long-lived free triplets in high yields by utilizing organic singlet fission materials can be the cornerstone for increasing photovoltaic efficiencies potentially. However, except for polyacenes, which are the most studied systems in the singlet fission field, spin-entangled correlated triplet pairs and free triplets born through singlet fission are relatively poorly characterized. By utilizing transient absorption and photoluminescence spectroscopy in supramolecular aggregate thin films consisting of Hamilton-receptor-substituted diketopyrrolopyrrole derivatives, we show that photoexcitation gives rise to the formation of spin-0 correlated triplet pair 1(TT) from the lower Frenkel exciton state. The existence of 1(TT) is proved through faint Herzberg-Teller emission that is enabled by vibronic coupling and correlated with an artifact-free triplet-state photoinduced absorption in the near-infrared. Surprisingly, transient electron paramagnetic resonance reveals that long-lived triplets are produced through classical intersystem crossing instead of 1(TT) dissociation, with the two pathways in competition. Moreover, comparison of the triplet-formation dynamics in J-like and H-like thin films with the same energetics reveals that spin-orbit coupling mediated intersystem crossing persists in both. However, 1(TT) only forms in the J-like film, pinpointing the huge impact of intermolecular coupling geometry on singlet fission dynamics