Application Of Liquid Crystal Molecules In Dye-Sensitized Solar Cells

Due to the increasing energy demand,people are committed to develop renewable resources to replace traditional energy sources,among which solar energy is the most widely sourced and researched.Dye sensitized solar cells(DSSCs),with their advantages of easy fabrication,low production cost and environmental friendliness,stand out from many types of solar cells and have become a hot research topic in the field of solar cells in recent years.Currently,the most widely used electrolyte in DSSCs is liquid electrolyte.Although high power conversion efficiency(PCE)can be achieved,the liquid electrolyte is easy to volatilize and leak,resulting in poor long-term stability of the device,so the development of electrolyte that can improve the long-term stability of the device has become an important issue.Since the absorption range of single sensitized dyes is narrow,using them alone in DSSCs will affect their photovoltaic performance.Co-sensitizing two or more dyes can better solve this problem,but using different co-sensitizers and cosensitization methods will have different effects on the photovoltaic performance of the devices.This thesis focuses on these two aspects.In this thesis,biphenyl-like liquid crystal molecules were synthesized by Williamson etherification reaction and applied to DSSCs devices as electrolyte additives and co-sensitizers,which are proposed to improve the photovoltaic performance and long-term stability of the devices.The main studies are as follows:(1)Three biphenyl-like liquid crystals(4OBC,5OBC and 6OBC)with different lengths of alkoxy chains were synthesized and added to the liquid electrolyte(I-/I3-)of DSSCs as additives,and the optimal electrolyte additive liquid crystal molecule was screened as 5OBC;evaluate the photovoltaic performance based on the addition of different concentrations of 5OBC to the liquid electrolyte The photovoltaic performance of DSSCs based on the addition of different concentrations of 5OBC to the liquid electrolyte was evaluated,and the optimal addition concentration was determined to be 5 wt%;based on this,the gel electrolyte was prepared by adding polymer(poly(vinylidene fluoride-co-hexafluoropropylene),and the photovoltaic performance of DSSCs based on liquid electrolyte,liquid crystal electrolyte and gel electrolyte were compared,and the results showed that their PCEs were 3.76%,4.05% and 1.79%,which is due to the fact that the addition of 5OBC to the electrolyte increases the transmission path of redox pairs and further improves the Short-Circuit Current Density(Jsc),and the addition of liquid crystal to the liquid electrolyte changes its viscosity and effectively inhibits the volatilization of the electrolyte,thus improving the long-term stability of the devices(after maintaining more than 90% of its initial PCE value even after 1000 h of assembling the device);(2)Three biphenyl-like liquid crystals with different alkoxy chain lengths(4OBC-CA,5OBCCA and 6OBC-CA)with carboxyl groups were synthesized and used as co-sensitizers to cosensitize with the acid dye NP-1 containing cyanoacetic acid receptor,and the DSSCs devices were assembled after 1 h of stepwise co-sensitization,and the optimal liquid crystal co-sensitizer was screened as 6OBC-CA.The optimal length of time was determined to be 1 h.After comparing the effects of different co-sensitization methods on the photovoltaic performance of the devices,the results showed that 1 h of gradual co-sensitization was still the optimal co-sensitization method,and the PCE of the device was 3.72%,and its long-term stability was also better(it could maintain more than 87% of its initial PCE value after assembling the device for 1000 h);(3)Two carboxylated liquid crystal intermediates(5BA and 5HHA)with different conjugate groups of π-bridge chains were used as co-sensitizers with the primary dye NP-1,and then the PV performance of DSSCs based on different co-sensitizers and different co-sensitization methods was evaluated,and the results showed that the best co-sensitization method was to add5 BA with its molar ratio of 60% to the primary dye NP-1 by the cocktail method,which obtained a better PCE(2.66%).In this thesis,we designed and synthesized different structures of biphenyl-like liquid crystal molecules,used them as electrolyte additives and co-sensitizers,studied the effect of the application of liquid crystal molecules on the photovoltaic performance of the devices,and obtained DSSCs devices with better performance,which has certain significance for the in-depth research in the field of electrolyte additives and co-sensitizers.