Constructing Bulk-Heterojunction With Long-Range Ordering And Its Photophysical Properties

Single-crystals,commonly considered as homogeneous solids,are able to be internally interfaced abnormally with guest macromolecules,which can be found in the biominerals where single-crystals incorporate surrounding biomacromolecules to reinforce their mechanical properties.This unusual combination between heterostructure and long-range ordering have attracted abundant investigations to reproduce their synthetic analogs and study the incorporation mechanisms,as well as to explore novel functions and expand the application scope.To date,an increasing number of guest materials have been found to be incorporated inside single-crystals.More importantly,among those guest materials with different aggregation states,gelnetworks confer a unique internal structure on single-crystals,i.e.the three-dimensional(3D)interpenetration.This facile strategy for constructing hetero-structures with continuous 3D interfaces guarantees a great potential of applying single-crystals in more material fields.For organic semiconductors,“long-range ordering” and “hetero-structure” are two of the key structural factors.On one hand,in comparison of amorphous or polycrystalline states,“long-range ordering” always leads to improved properties of carrier transport(mobility),as well as exciton diffusion.A high mobility eventually results in a superior performance of single-crystal-based organic field-effect transistors(OFETs).On the other hand,“hetero-structure” guarantees a significant process,i.e.charge separation or recombination,in photoelectric conversion materials.More importantly,it has been demonstrated that charge separation can be benefit by ordering.Thus,the combination of “long-range ordering” and “hetero-structure” is of significance and has attracted a lot of scientific interests.In contrast to planar heterojunctions with long-range ordering,it is difficult to achieve long-range ordering in bulk-heterojunctions(BHJs)with continuous 3D interface.Instead,due to the enormous nucleation events occurred inside the conventional donor-acceptor blends,only short-range ordered BHJs have been fabricated,which limits the further development of photoelectric conversion devices.Essentially,the bio-inspired gel-preparation method gives a well-controlled crystallization kinetics to grow single-crystals with incorporation of surrounding gelnetworks,leading to the combination of continuous 3D hetero-structure and long-range ordering.Thus,this strategy can be a promising solution for preparing long-range ordered BHJs.Owing to the lack of corresponding research,this thesis started from studying the feasibility and possible controlling factors of gel-incorporation into organic semiconducting single-crystals.Then,we successfully prepared long-range ordered BHJs based on conjugated polymer networks and single-crystals of organic small molecules.Moreover,the better photophysical properties,as well as the application potentiality,were demonstrated by taking charge-transfer property as an example.In chapter 1,we produced a primary review of the progresses in the synthetic polymer/single-crystal composites with guest species incorporated inside crystal hosts.The varied components and their aggregation in different states(isolated aggregates and continuous matrices)are summarized.In addition,the possible mechanisms and controlling factors(physical and chemical properties of guest species and crystallization kinetics)that governing the incorporation processes are discussed.Finally,typical application prospects of these incorporation strategies are introduced,including mechanical reinforcement,bandgap engineering,catalyst,self-healing,drug delivery and optoelectronic devices.In chapter 2,we use silica gel media,instead of the normally used solutions,to grow single crystals of two typical organic semiconductors,anthracene and 9,10-diphenylanthracene(DPA).We demonstrate that gel networks will be incorporated into the single crystals to form bulk contacts once the silica gels are appropriately modified to enhance the affinity between the gel networks and the crystals.In chapter 3,we construct long-range ordered BHJs between the well-known BHJ model pair,poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenvinylene](MEH-PPV)as donor and C60 as acceptor.The growing C60 crystals incorporate the MEH-PPV networks to form composites.The networks of MEH-PPV nanofibers penetrate through the C60 crystals without destroying their single-crystal nature,resulting in BHJs with long-range ordering.Compared to the conventional BHJs with short-range ordering,a faster charge-transfer process and improved performance of photodetection in the longrange ordered BHJs have been found.the BHJs with long-range ordering provide a platform to deepen the fundamental knowledge and to construct high-performance optoelectronic devices of organic heterojunctions.Moreover,through the same method,thick Cz PSF fiber-networks were also introduced into DPA single-crystals with 3D interpenetrated structure.In chapter 4,ribbon-like TIPS-pentacene single-crystalline thin films were obtained on P3 HT films with morphologies of continuous fiber-networks or porous templates.P3 HT films with both structures were incorporated into single-crystals,forming heterojunctions with both continuous 3D interfaces and long-range ordering.