Heterocyclic Compounds Induced Crystal Growth Regulation And Defect Passivation For Perovskite Films

In the few years since the discovery of perovskite solar cells,their photoelectric conversion efficiency has exceeded 23%,which is comparable to the commercial polysilicon solar cells.The quality of perovskite film is the most critical factor determining the performance of perovskite solar cells.The benchmark CH₃NH₃PbI₃ films prepared by the broadly practiced one-step spin-coating procedure are usually defective due to the uncontrollable crystal growth obtained in this procedure,undesirably resulting in in-situ and surface defects,which limits the performance of perovskite solar cells.In this thesis,we add thiazole as an additive to the perovskite?CH₃NH₃PbI₃?precursor solution,successfully modulated the microenvironment for the nucleation and growth of perovskite crystals using a one-step coating procedure.The lone pair electrons on S and N in the thiazole molecule can react with Pb atom,which can help in the formation of stronger and more covalent bonds at the interfaces and thus passivate defects.Using solvent annealing during annealing process can induce further surface recrystallization,which can effectively improve the morphology of perovskite film and suppress defects.The perovskite solar cells fabricated by our method exhibit an ultrahigh fill factor?FF?of 0.82,a photoelectric conversion efficiency?PCE?of 17.98%,which was25%higher than the control devices in the absence of the thiazole additive.Moreover,the stability of perovskite solar cells of unencapsulated devices based on CH₃NH₃PbI₃ with adding thiazole have been improved.After 60 min of exposure of constant illumination?100 mW/cm²?at room temperature in ambient air?RH,50-60%?,the PCE of the thiazole-based device retained 70%.Solvent engineering is one of the effective methods to improve the quality of perovskite.The surface of the perovskite film washed by anti-solvent have a lot of defects,which will limit the efficiency of the devices.In this thesis,pyridine was added as an additive to the anti-solvent chlorobenzene?CB?.When the anti-solvent was used to wash CH₃NH₃PbI₃,the lone pair electrons on the N atom in pyridine molecule will react with the uncoordinated metal ions on the surface,which can passivate dangling bond in the surface,reduce carrier recombination,and improve the performance of the perovskite solar cell.In this thesis,Pyridine/CB mixed anti-solvent was prepared at different volume ratios.The test results showed that the perovskite solar cell has the best performance when V?Pyridine?/V?CB?=0.02,the bulk carrier recombination is reduced.The photoelectric conversion efficiency is 16.4%,which is 8.5%higher than that of the device without adding pyridine.Through the work of this thesis,we found that thiazole and pyridine can effectively regulate the crystal growth of perovskite film,passivate crystal defects and improve the quality of perovskite film,thereby improving the performance of perovskite solar cells.