The Research Of Doping And Spacer Cations Tuning For Highly Efficient All-Inorganic And Quasi-Two-Dimensional Perovskites Solar Cells

Organic-inorganic hybrid three-dimensional（3D）perovskite solar cells（PSCs）have been considered the most promising photovoltaic due to the excellent photoelectrical properties,simple fabrication processes and low fabrication price.Up to date,the best-certified power conversion efficiency（PCE）of PSCs has reached 25.7%,approaching those of crystalline silicon solar cells.However,the commercialization of PSCs has not been realized.One of the most important reasons is the poor stability of perovskite materials.Organic-inorganic hybrid 3D perovskite materials are easily to degradation under high temperature,high humidity,or strong light irradiation conditions,which also lead to the decrease of the PCE of corresponding PSCs.To improve the stability of PSCs,various methods have been proposed.Among them,the use of Cs-based all-inorganic perovskite and quasi-two-dimensional（Q-2D）perovskite materials as light absorption materials in PSCs to fabricate all-inorganic PSCs and Q-2D PSCs can effectively improve the stability of PSCs under high temperature,strong light irradiation or humidity conditions,respectively.However,due to the high defect tolerance of all-inorganic perovskite and the insulating properties of organic spacers in Q-2D perovskites,their corresponding PSCs have low PCEs.In this dissertation,the high-quality all-inorganic perovskite and Q-2D perovskite films with less defects and strong conductivity have been fabricated to improve the PCE of corresponding PSCs by doping and spacer cations tuning of perovskite materials.The specific work is as follows:（1）A simple hot-casting method has been employed to fabricate high-quality Cs Pb I₂Br films under a relatively low-temperature（120℃）annealing processes,which overcome high temperature for phase transition.By using of traditional spin-coating processes,the prepared Cs Pb I₂Br films contained much voids with small grain-sizes and poorly crystallization.By contrast,the phase transition temperature of Cs Pb I₂Br perovskite decreased from 340℃to 120℃by hot-casting processes,which is to form compact,large-grain and pinhole-free Cs Pb I₂Br films.During the hot-casting processes,the decreased phase transition temperature and improved films quality is mainly related with Cs Pb Br₃ middle-phase.As a result,the hot-casting processed Cs Pb I₂Br PSCs exhibited an outstanding PCE of 13.80%,which is much higher than that（2.91%）of the traditional spin-coating processed Cs Pb I₂Br devices.（2）By using a small amount of zinc acetate（Zn（Ac）₂）as additive doping into precursor solution to prepare high-quality Cs Pb I₂Br film,which overcame the shortcoming of short carrier diffusion length in all-inorganic perovskite.The synergistic effects of Zn²⁺and Ac^-in Cs Pb I₂Br film are also researched.On the one hand,the Zn²⁺would partially replace the Pb²⁺in Cs Pb I₂Br crystal lattice to enhance the phase stability ofα-Cs Pb I₂Br phase and conductivity of perovskite film.On the other hand,the halide divacancy defects at grain boundaries would be passivated by the coordination between Ac^–and uncoordinated Pb²⁺to reduce non-radiative recombination.As the effects of Zn（Ac）₂,the carrier diffusion lengths（L_D）are determined to be longer than 1μm,which would realize high efficient carrier transport and collection in Cs Pb I₂Br films.Compared with the pristine PSCs,the champion PCE of the PSCs is increased from 12.31%to 14.93%upon doping with Zn（Ac）₂,which is mainly attributed to the increased open-circuit voltage(V_OC)and fill factor（FF）.Furthermore,the non-encapsulated Zn（Ac）₂ doped PSCs show good stability in air.（3）By tuning chemical structure of Phenethylamine（PEA）spacer cation to prepare high-quality Q-2D perovskite films and efficient PSCs.The spacer cation tuning is achieved with halogen（F,Cl,Br）substitution to obtain F-PEA,Cl-PEA,Br-PEA based Q-2D perovskites.On the one hand,the halide substitution could suppress the formation of parallel oriented n=1 2D perovskite and thus leads to the crystal orientation perpendicular to substrates.On the other hand,PEA and F-PEA based Q-2D perovskite exhibit ordered perovskite phase distribution in films with large n-phases near the top-side and small-n phases near the bottom-side;while the Cl-PEA and Br-PEA based films exhibited an almost random distribution of small-n and large-n phases.This ordered phase distribution is beneficial for the formation of type-II band-alignment,facilitating charge carrier transport in perovskite films.Additionally,F-PEA based Q-2D perovskite films shows a significantly enhanced crystallinity and improved film quality.As a result,F-PEA based PSCs achieve a PCE of 18.10%,significantly higher than those of Cl-PEA（7.93%）and Br-PEA（6.08%）based PSCs.Moreover,the F-PEA based devices exhibit remarkably improved stability under humid or high-temperature conditions.（4）By fluorinating Benzylamine（BZA）spacer cation to prepare high-quality Q-2D perovskite films and efficient PSCs,which enhanced charge transport rates of perovskite films by constructing a new charge transport channel in organic spacer layer.It has been found that fluorination of spacer cation can slow down the crystallization rate of perovskites,resulting in the formation of perovskite grains with large-size and vertical alignment in Q-2D perovskite films.The interaction between the adjacent spacer cations is further enhanced after fluorination,which would construct a new charge transport channel to enhance the carrier mobility of Q-2D perovskite enormously.Furthermore,the fluorination also improves the perovskite film quality and reduces the trap-density.As a result,compared with the pristine PSCs,the F-BZA based PSCs achieve a champion PCE of 16.82%with lower hysteresis and better long-term stability.On the whole,in this study,not only overcame charge carrier loss in all-inorganic perovskite to prolong carrier L_D,but also enhanced charge transport rates in Q-2D perovskite.Meanwhile,high-quality all-inorganic perovskite films and Q-2D perovskite films,as well as high performance PSCs,are prepared by compositional regulation,which overcome the poor stability of PSCs.These researches provides a novel insight for improving device performance for all-inorganic and Q-2D PSCs and has significance as a reference for the commercialization of PSCs.