Research On Optoelectronic Devices With Micro-nano Structures

There has been a thriving development in nanotechnology since its appearance in the mid-50s in the last century.Preparation of nanomaterials and exploration of their properties has been a research hotspot in scientific research.Many approaches were thus developed to fabricate micro/nano structures,such as focused ion beam lithography,holographic lithography,colloidal lithography,block copolymer self-assembly arose and developed continuously.These techniques,however,are restricted by expensive procedure or limited area which severely limits their further development and industrial application.Among them the nanoimprint lithography has gained widespread attention because of its advantages such as high efficiency,large area,and low cost.Micro/nano structures and materials,as the basic components of solar cells or other optoelectronic devices,demonstrated unique optical,electrical,and mechanical properties for these micro/nano devices providing a new way to implement new types of flexible photonic and electronic functional devices.By optimizing the design and construction of the micro/nano structures,an equivalent gradient refractive index change can be formed in the window layer of the optoelectronic device to suppress reflection or generate surface plasmon resonance enhanced light absorption near the metal nanostructure,thereby improving the performance of the devices.The researches of micro/nano structures and devices with these overall characteristics have important scientific significance and application value.In this work,we aimed to develop micro/nano fabrication technologies,fabricate different the micro/nanostructures,study the formation mechanism of micro/nanostructures and explore their new characteristics such as light management,electrical properties and mechanical properties.Finally,the performance of flexible optoelectronic devices integrated micro/nanostructured was investigated.The specific work is as follows:(1)Firstly,the large scale highly oriented nanopatterns on Al foils were obtained by full-field nanoimprinting lithography using soft stamps and post-etching processes.And then high ordered anodic aluminum oxide(HOAAO)films with both straight nanochannels and inverted cones can be rationally obtained by the following anodization and selective etching process.In addition,the growth mechanism of AAO was revealed by electric field simulation.It was found that AAO self-assembly growth could be better guided by secondary anodization,resulting in a more regular AAO template.The proposed scheme is compatible with roll-to-roll processing for massive production,and holds potential to be extended to the highly ordered anodized TiO2 nanotubes.As a demonstration,electromagnetic simulations of CH3NH3PbI3 thin-film photodetectors on the large area HOAAO films with tunable nanostructures were performed.It could provide a versatile platform for high-performance optoelectronic devices.The result shows that the device with inverted nanocone substrate has a higher absorption than the traditional flat surface device within a broad wavelength range.It indicates that the large-area HOAAO films with tunable morphologies could provide a versatile platform for high-performance optoelectronic devices with feasible optical management strategy.(2)We proposed an approach to realize highly ordered metal oxide nanopattems on polyimide(PI)substrate based on the sol-gel chemistry and soft thermal nanoimprinting lithography.Thin film amorphous silicon(a-Si:H)solar cells were subsequently constructed on the patterned PI flexible substrates.The remarkable and broadband enhancements in optical absorption and quantum efficiency were realized on NH device with nanohole array back reflector and the PCE value up to 8.17%was achieved.In addition,flexible transparent nanocone films,obtained by template process,were attached onto the patterned PI solar cells serving as top anti-reflection layers.The PCE performance with these dual-interfacial patterns raised up to 8.17%that is improved by 48.5%over the planar device.The imprinted inorganic oxide nanostructures possess outstanding thermal,chemical and mechanical stability,which can be directly integrated with various thin film solar cells with high temperature tolerance.The flexible device experienced little PCE drop even after 100,000 bending cycles.The electromagnetic simulations confirm the measurements and uncover the mechanisms of anti-reflection and the surface plasmon resonance.Although the work was conducted on a-Si:H material,our proposed scheme can be extended to a variety of active materials for optoelectronics application.Additionally,by employing the UV-curable inorganic oxide-organic composites and roll-to-roll process,the production of photonic structures would be more efficient.(3)Transparent electrodes consisting of silver nanowires(AgNWs)and highly ordered zinc oxide nanopatterms were fabricated based on the sol-gel chemistry and soft thermal nanoimprinting lithography.The unique structural features of our ZnO/AgNWs composite layers allow for a novel transparent conducting electrode with unprecedented excellent adhesiveness,the the sheet resistance(?12?/sq).and thermal stability(?400?),as well as flexibility and good optical transparency.The patterned ZnO layer allows more effective light transmission at the visible wavelengths due to the reduced specular reflectance,while maintaining a high electrical conductance.The patterned ZnO layer conformally covers the AgNWs filling the empty area and tightening the AgNWs junctions,and it may act as an encapsulate that protects the nanowires from oxidation/melting,improving the mechanical and thermal stabilities of the embedded AgNWs film.Our patterned ZnO/AgNW composite also serves well as an effective window electrode for solar cells.The PCE of the device arrived at 7.51%.The solar cells incorporating this composite electrode exhibited improvements of 10.8%and 5.0%in short circuitcurrent and energy conversion efficiency respectively compared to the device based on AgNWs electrode.(4)We developed a facile and scalable peel-off transferring process to fabricate the substrate-free a-Si TFSCs.Graphene was used as the interlayer between the donor substrates of Si/SiO2 and the a-Si solar cells and led to a more than 44%decrease of the adhesion strength during peel-off process.Furthermore,the structured polyethylene terephthalate(PET)was used as an effective anti-reflection film to manage the light travel path and utilize the light inward promoting the broadband and omnidirectional enhanced performance of the device.The structured PET-based a-Si device shows the energy conversion efficiency(?)up to 5.98%and weight specific power up to 140.04 W/Kg,which are improved by 16.0%and 246.3%,respectively,over the Si/SiO2-based device.Especially,as the incident angle of?=60°,the ? and weight specific power possess an absolute enhancement of 44.1%and 330.2%,respectively,over the Si/SiO2-based as fabricated device.Overall,this work demonstrates a viable and simple route toward fabrication of highly efficient and light weight flexible substrate-free TFSCs.We believe that the peel-off transferring process can be extended to other kinds of solar cells,optoelectronic devices like photodetectors,light emissions and so on,and can potentially be further developed into larger-scale manufacturing in the future,as well.