Fabrication And Properties Of Low-cost Counter Electrodes For Fiber-shaped Dye-sensitized Solar Cells

As one of the most promising photovoltaic technologies, much attention has been paid to dye sensitized solar cells (DSSCs). In recent years, great progress has been achieved in the preparation and photovoltaic performance of DSSCs. Conventional planar dye-sensitized solar cells (PDSSCs) are made of rigid plates, which are unfavorable for portable applications due to the fragile and poor flexible of substrate. As a result, fiber-shaped dye-sensitized solar cells (FDSSCs) were proposed to meet the portable and wearable electronic devices. FDSSCs, which most common use flexible metal wire, carbon fibers etc. as conductive substates, could be assembled into electronic textiles (clothes, hat etc.) though knitting technology. Therefore, more and more research efforts on FDSSCs are carried out. The typical counter electrode (CE) of FDSSC is Pt wire with high conductivity and electrocatalytic activity, which hinders the scale of production and application of FDSSCs due to the rarity, expansive, and high-energy-consuming procedure of Pt. This dissertation aims to develop the controllable preparation of low-cost, high-performance Pt-free cathode materials, and investigate electronical properties, catalytic sites and I3-/I- diffusion rate in catalytic activity layer to design and construct microscopic nanostructure of CE. The details are summarized as follows:(1) A low-cost, Pt-free CE materials consisting of porous, single crystalline titanium nitrides (TiN) nanoplates grown on carbon fibers (CF) through a simple two-step approach. The FDSSC based on the TiN-CF CE shown high conversion efficiency of 7.2%, superior to Pt wire CE (6.23%). The single crystallinity of TiN rapidly transported electrons. The mesopores on the TiN nanoplate endow the TiN with more active sites. The large macropores generated through the intercrossing of the nanoplates provide number of active sites and transport tunnels for I3-/I- diffusion throughout the TiN layer. Therefore, TiN-CF shows excellent electrochemical performance.(2) One-step fabrication of both CoNi2S4 nanoribbons and nanorods on carbon fibers (CF) as CEs for FDSSCs. CoNi2S4 nanoribbons-CF-based FDSSC achieved high conversion efficiency of 7.03%, superior to Pt wire CE (6.45%), which demonstrates that the present CoNi2S4 nanoribbon-CF possesses both the promising electrical conductivity and catalytic activity needed for high efficient operation and low cost manufacture. CoNi2S4 nanorod-CF-based FDSSC achieved conversion efficience of 4.1%, inferior to CoNi2S4 nanoribbon-CF CE. Comparing to CoNi2S4 nanorod, the exposed crystal facet of CoNi2S4 nanoribbon possesses more active sites, which might be responsible for its high electrochemical performance.(3) Single-crystalline metal (Co, Ni) selenium (Co0.85Se or Ni0.85Se) nanosheets were in situ grown on metal (Co, Ni) fibers (M0.85Se-M). Both M0.85Se-M (Co0.85Se-Co and Ni0.85Se-Ni) fibers prove to function as excellent, low-cost CEs in FDSSCs. The M0.85Se have some advantages:(1) the intrinsic electrical property of the single-crystalline M0.85Se; (2) the enough void space among M0.85Se nanosheets allows the redox ions easier diffusion, and the large contact area between the CE catalytic material and electrolyte; (3) in situ direct growth of the M0.85Se on metal fiber renders the good electrical contact between the active material and the electrons collector. FDSSCs, which based on Co0.85Se-Co and Ni0.85Se-Ni, shown high conversion efficiency (6.55% and 7.07%, respectively), and they are comparable or even superior to Pt fiber CE (6.54%).