Effects Of Additives On The Photoelectric Properties Of Organic-inorganic Hybrid Perovskite Solar Cells

In this dissertation,we focus the impact of different kinds of additives such as tetraethyl orthosilicate(TEOS)and inorganic anions into CH₃NH₃Pb I₃perovskite precursor solution on improvement of the perovskite nucleation and defect passivation of perovskite layer.On one hand,the impact of additive engineering on improvement of the perovskite morphology,crystal structure and optical properties was systemically characterized by SEM?XRD?PL?UV-vis and etc.On the other hand,the impact of additive engineering on the carrier transport and recombination process was systemically characterized by EQE?J-V?EIS and etc,which reveals the relationship among device performance,interfaces and carrier transport and recombination process.The following is the main contents of this dissertation.(1)The impact of tetraethyl orthosilicate additive on the performace of planar perovskite solar cells.Trap passivation can be enhanced by introducing the controlled tetraethyl orthosilicate(TEOS)additive into the perovskite precursor.The effect of different concentrations of TEOS additive on interfacial modification and carrier recombination process has been investigated systematically.Silicon dioxide(Si O₂),the product of TEOS additive,can precipitate at the grain boundary after the formation of perovskite film,resulting in trap passivation at perovskite interface.The recombination kinetics manifests that a small amount of TEOS additive can significantly prolong carrier lifetime,due to the reduction of trap-states in the perovskite interface,which are supposed to be the carrier recombination centers.Using a typical planar structure of the cells prepared under fully open air condition,the steady-state efficiency of our best-performing devices has increased by 15%,which is improved from 15.96 to 18.38%,electron lifetime increased from 0.44ms to 1.88ms.(2)The impact of halogenide anions additive on the performace of planar perovskite solar cells.By using PbCl₂ as an additive to the perovskite precursor and a rapid one step solution approach with ethyl acetate as anti-solvent,high quality CH₃NH₃Pb I₃ films were achieved.The devices based on different concentrations of PbCl₂ additive were fabricated.It is found that the perovskite layer with large grain size was achieved via thermal annealing steps as the precursor solution was added with 2.5mol%of PbCl₂additive.Every perovskite thin film with such an additive exhibits a higher surface coverage with a reduced pinhole size and higher crystallization compared with that without the additive.It is found that the precipitated Pb I₂can fill in the grain boundary and passivate trap-states in the perovskite interface.Using a typical planar structure of the cells with 2.5mol%of PbCl₂ additive,the steady-state efficiency of our best-performing devices has increased by 12%,which is improved from 16.13 to 18.06%.(3)The impact of SCN anions additive on the performance of planar perovskite solar cells.By using Pb(SCN)₂ as an additive with different concentrations to the perovskite precursor,high quality CH₃NH₃Pb I₃ films were achieved via thermal annealing steps.For the perovskite precursor with 5mol%of Pb(SCN)₂additive,adjust the molar ratio of Pb(SCN)₂ and CH₃NH₃I,its effect on interfacial modification and carrier recombination process has been investigated systematically.The longer diffusion length of carrier can be attributed into the enlarged perovskite crystalline grainthin film with higher surface coverage and higher crystallization compared with that without the additive.It is found that the precipitated Pb I₂can fill in the grain boundary through SCN^-coordination on interfacial modification and passivate trap-states in the perovskite interface.The the steady-state efficiency of the best divices based on 5mol%of Pb(SCN)₂ additive and 1:3 of the molar ratio of Pb(SCN)₂ and CH₃NH₃I,has increased by 15%,which is improved from 16.13 to 18.60%.