High Performance Fiber-shaped Solar Cells

Integration, miniaturization, light weight and flexibility are the mainstream direction for the portable and wearable devices. Currently, traditional silicon-based solar cells and organic solar cells always presented in a planar formats, which cannot fully satisfied the evergrowing requirement for mobile devices and wearable electronics. Fiber-shaped solar cells emerged as a promising solution in recent years. Compared with planar solar cells, they are highly integrated, more flexible and lightweight, and provide all-around surface available for illumination. Furthermore, they can be woven into textiles as conventional chemical fibers. However, most of fiber-shaped solar cells are fragile because of their rigid fiber materials adopted, which cannot afford a deformation during use. Developing stretchable fiber-shaped solar cells can overcome this vulnerability. This dissertation, for the first time, demonstrated high efficiency fiber-shaped dye-sensitized solar cells (DSCs) based on graphene and carbon nanotubes, then developed stretchable DSCs and integrated devices. Finally, we explored the performance of photovoltaic textile.High-efficiency fiber-shaped DSCs. It is critical to develop high performance electrode materials to improve the cell efficiency. In this dissertation, graphene/platinum nanoparticle composite fibers were synthesized by electrochemically depositing platinum nanoparticles onto the graphene fibers, which were prepared by a wet spinning method. These composite fibers exhibited remarkable electrical conductivity and catalytic activities. Then, the composite fiber was used as the counter electrode in the fiber-shaped DSC, with a modified titanium wire as the working electrode. After optimizing the materials and structure of electrode, the resulting DSC was recorded a certified maximum energy conversion efficiency of 8.45%, which is the highest efficiency ever reported for fiber-shaped or wire-shaped solar cells. With deeply study the mechanism and principle of the solar cells, it was found that uniform and small platinum nanoparticles were firmly deposited on the graphene fibers, which is due to the good affinity between the graphene and nanoparticles. This morphology exhibited higher surface area and better catalytic activity, which was beneficial to the photovoltaic performance.Stretchable fiber-shaped DSCs. Stretchable fiber electrode is the key to construct stretchable fiber-shaped DSCs. In this dissertation, elastic conducting fibers were prepared by winding aligned multi-walled carbon nanotube sheets on rubber fibers by a rotation-translation method. The as-prepared fibers showed high and stable electronic properties even under stretching with a strain of 100%. Likewise, a modified Ti wire as the working electrode was twined onto the elastic conducting fiber to construct a stretchable fiber-shaped DSC, which demonstrated a high energy conversion efficiency of 7.13%, which was well maintained under a strain of 30%.Stretchable fiber-shapedintegrated device to simultaneously realizing energy conversion and storage. For the fiber-shaped solar cells, how to store the electricity converted from the solar power and output when needed remains a great challenge. In order to solve this problem, in this dissertation, a stretchable fiber-shaped supercapacitor was integrated with a stretchable fiber-shaped supercapacitor to fabricate a stretchable fiber-shaped device integrated with energy conversion and storage. First, a stretchable fiber-shaped supercapacitor was fabricated by a rotation-translation method, whose specific capacitance remained ～19.2 F/g when stretched to a strain of 75%. Then, it was integrated with the stretchable fiber-shaped DSC in a coaxial structure to realize both energy conversion and storage. The entire energy conversion and storage efficiency of the integrated device yielded 1.83%, which can also sustain 50 cycles of stretch.Fiber-shaped solar cell based photovoltaic textile. The fiber-shape solar cells can be woven into photovoltaic textiles, which represents a dramatic advantage over the planar devices. In this dissertation, the high performance fiber-shaped DSCs were woven into photovoltaic textiles with high flexibility and stability, which exhibited high performance during bending and stretching. Meanwhile, the output currents and voltages can be tuned by parallel and series connections, respectively.In summary, this dissertation presented stretchable, efficienct, integratable and weavable fiber-shaped DSCs based on carbon nanomaterial fibers. The rapid charge separation and transport at the interface of carbon nanomaterials are carefully studied. This dissertation provides a general and effective strategy in the advancement of fiber-shaped solar cells and stretchable and wearable electronics.