Bismuth Iodide (BiI₃) Sensitized Solar Cells

The increasingly serious problem of global warming and the shortage of nonrenewable fossil fuels have made us focus on excellent green,renewable and clean energy.Studies show that solar energy reaching the earth in one hour can meet the global energy demand for one year.Therefore,the development and application of solar energy brook no delay.Among them,the solar cell,which converts solar energy into electricity is an important means of rational development of solar energy.The development and utilization of new materials have led to the rapid development of third-generation solar cells in the last decade,but also expose their defects.In the thirdgeneration solar cells,metal chalcogenide semiconductors and lead-based perovskite structure crystals are highly toxic and pollute the environment.Therefore,it is important to find non-toxic and stable green alternative materials as light absorbers.To address this issue,this paper explores bismuth iodide（BiI3）as an alternative light absorbing material that may have excellent photoelectric properties,and studies its photoelectric properties when applied to solar cells.The main contents are as follows:1.Pure water-based liquid electrolyte applied to bismuth iodide（BiI3）sensitized solar cellsBismuth iodide nanoparticles were synthesized by hydrothermal method,dissolved in tetrahydrofuran（THF）solvent to make a solution,and loaded on FTO/TiO2 by spin coating to make bismuth iodide sensitized photoanodes.A pure water-based liquid electrolyte was used to encapsulate the sensitized solar cells and test the photovoltaic performance of the devices.Based on this,further optimize the waterbased liquid electrolyte.Add surfactant Triton X-100 to reduce the interfacial tension between the electrolyte and photoanode phases,increase the wetting of the liquid electrolyte on the photoanode film to provide more positive carrier transport.In addition,the relationship between the thickness of the metal semiconductor oxide film on the photoanode and the loading of BiI3 and the performance of solar cell devices was discussed.Studies have shown that the short-circuit current density（Jsc）of bismuth iodide（BiI3）solar cells prepared by using a photoanode with a TiO2 film thickness of 18μm on the photoanode and a water-based liquid electrolyte added with the surfactant Triton X-100 as hole transport is 11.34 mA/cm2,the open circuit voltage（Voc）is 0.61 V,and the photoelectric conversion efficiency（PCE）of the cell is 2.50%.2.Application of new phosphate passivation layer in bismuth iodide（BiI3）sensitized solar cellBased on the bismuth iodide solar cell prepared in the previous work,a new phosphate passivation layer was applied to the bismuth iodide sensitized solar cell to passivate the photoanode in order to further improve the photovoltaic performance of the device.The passivation layer formed by the phosphating product inhibits the charge recombination between the photoanode and the liquid electrolyte inside the cell,hinders the reverse transfer of charge between the photoanode and the electrolyte interface,and increases the probability of the forward transfer of carriers.Improve the short-circuit current density of bismuth iodide solar cells,suppress dark current generation,and increase the open circuit voltage of the device,thereby improving the photoelectric performance of bismuth iodide solar cells.It is shown that the phosphate passivation layer with different metal cations has a certain slowing effect on the charge recombination of bismuth iodide solar cells.Among them,the ZnPh phosphate passivation effect is the most obvious.Combined with the phosphating process at different temperatures,the passivation effect of the ZnPh passivation layer phosphating at room temperature,medium temperature and high temperature on the bismuth iodide sensitized solar cell was studied.The results show that the ZnPh passivation layer at room temperature is effective in passivating bismuth iodide solar cells,and the shortcircuit current density（Jsc）reaches 14.47 mA/cm2,the open-circuit voltage（Voc）reaches 0.60 V,and the photoelectric conversion efficiency（PCE）of the device has reached the highest efficiency of bismuth iodide sensitized solar cells reported in the literature,3.45%.