Research On Fabrication Of Bismuth-based Perovskite Thin Film And Its Application In Solar Cells

Perovskite solar cells（PSCs）have attracted great attention in the field of photovoltaic technology due to their simple process,low cost and high photoelectric conversion efficiency（PCE）.Recently,the PCE of lead-based PSCs has been improved to 25.2%,which is comparable to traditional crystalline silicon solar cells.However,to achieve the final commercialization of PSCs,two main problems seem to be solved,namely stability and toxicity.In view of the above two shortcomings,it is of great significance to explore stable and non-toxic perovskite alternative materials.Bismuth-based perovskites have become the potential candidate for the lead-free perovskites because they are non-toxic and show high stability in air.At present,bismuth-based PSCs have achieved a PCE of about 3.6%,which is relatively low compared to lead-based and tin-based PSCs.This thesis focuses on improving the performance of bismuth-based PSCs through the optimization of preparation technology,additives engineering to improve the quality of perovskite films and interface optimization.Related research mainly includes the following aspects:（1）Two component ratios of bismuth-based perovskite materials(Cs Bi₃I₁₀ and Cs₃Bi₂I₉)were prepared through the precursor composition control.The results show that the photoelectric response of the perovskite film based on the Cs Bi₃I₁₀ structure is greatly broadened and higher short-circuit current density can be obtained.For the Cs Bi₃I₁₀ perovskite film,by optimizing the dropping time of the chlorobenzene antisolvent,a higher quality film can be obtained.The effects of the Cs Bi₃I₁₀concentration in precursor solution on the surface morphology,UV absorption spectrum and crystallinity of the perovskite film were further explored.Finally,under the best preparation conditions,the best PCE of Cs Bi₃I₁₀ based PSCs was 0.21%.（2）The morphology of the Cs Bi₃I₁₀ film was further optimized by additives engineering.The effects of three different additives including ammonium thiocyanate（NH₄SCN）,methylamine chloride（MACl）and citric acid（CA）on the quality of the perovskite film are compared.The results show that the influence of NH₄SCN and MACl on the performance of the device is not very significant.In comparison,the effect of CA additives on the device performance is much obvious.Through the optimization of citric acid in N,N-dimethylformamide（DMF）solvent,an ordered two-dimensional Cs Bi₃I₁₀ nanosheets can be prepared.The thin film is more conducive to charge transport.The PCE of Cs Bi₃I₁₀ based PSCs was increased to 0.56%.（3）Using 4-tert-butylpyridine and lithium bis（trifluoromethanesulfonyl）imide（t BP-Li TFSI）complex as additives for the poly[bis（4-phenyl）（2,4,6-trimethylphenyl）amine]（PTAA）hole transport materials（HTMs）could suppress the corrosion process on Cs Bi₃I₁₀/HTM interface caused by t BP.The PCE of Cs Bi₃I₁₀ based PSCs based on HTMs with t BP-Li TFSI complex additive was increased to 0.74%.It maintained about 90%of its initial PCE value after over 25 days,demonstrating higher device stability.In addition,the introduction of trioctylphosphine oxide（TOPO）passivation layer on the Cs Bi₃I₁₀ film could reduce the defects,suppress the non-radiative recombination,and improve the air stability of the perovskite film.The final PCE of Cs Bi₃I₁₀ based PSCs reached to 0.79%.Through the above related works,we hope to provide some valuable methods to improve the device performance and pave the way for the development of bismuth-based PSCs.