Preparation Of Perovskite Films By Sequential Deposition Method And Its Application In Perovskite Solar Cells

With the continuous development of human society,the world has two major problems:energy crisis and environmental pollution.One of the most effective and promising ways to solve these problems is to convert the solar energy into electricity,and solar cells is the key of photovoltaic technology.Recently,perovskite solar cells(PSCs)have attracted intense attention due to its superior properties of solution process ability,high charge carrier mobilities,tunable optical properties and large absorption coefficient.With a surprising increase of the power conversion efficiency(PCE)from 3.8%to 22.1%during last 7 years,today,it has become the fastest growing and the most promising solar cell technology.Currently,various processes have been developed to prepare the perovskite films in PSCs,and sequential deposition method is one of most classical approach.In this dissertation,we started our research from the preparation method of the perovskite active film,and studied the process and mechanism of perovskite film prepared by sequential deposition method and its effect on the electronic recombination kinetics process and the photovoltaic performance of PSCs emphatically.Firstly,we studied the effects of the structure and morphology of the electron transport layer on the perovskite films prepared by sequential deposition method.We constructed a consecutive compact and mesoporous(CCM)TiO2 film to substitute the compact blocking layer and scaffold layer for mesoscopic PSCs.The consecutive structure could reduce the interface resistance and help to the transport of electrons for mesoscopic PSCs,and therefore the charge recombination of the device was decreased effectively.Furthermore,due to the existence of macropores in the CCM TiO2 film,it is propitious to the deposition of perovskite and charge separation for the perovskite layer.Compared with Meso-PSC,the CCM TiO2 film based mesoscopic PSCs had achieved a higher PCE and better photovoltaic performances consistency.Secondly,the morphology of PbI2 films plays a key role for the preparation of high quality perovskite films during the sequential deposition process of perovskite films.Herein,we developed an in-situ pre-wetted PbI2 nano-sheet array film(HP-PbI2)to achieve high-quality CH3NH3PbI3(MAPbI3)perovskite films via sequential deposition.By introducing a small amount of hydrogen chloride isopropanol solution(IPA HCl)into the PbI2 precursor solution,an in-situ pre-wetted PbI2 nano-sheet array film was obtained.This novel porous PbI2 nano-sheet array film could accelerat the reaction between PbI2 and MAI,then a smooth,continuous,uniform,dense and PbI2-free MAPbI3 film was prepared.Compared to the devices prepared from the conventional PbI2 film,the PCE was enhanced from 12.89%to 19.19%under optimum addition amount of IPA HCl.Furthermore,the stability and consistency of the devices also had been improved significantly.Furthermore,the residual PbI2 in the perovskite film would lead to inferior performance of devices,such as,low power conversion efficiency(PCE),poor reproducibility and weak air stability.In this work,we developed a sandwich structure MAI-PbI2-MAI precursor film to prepare PbI2-free CH3NH3PbI3 perovskite film.In comparison to the sequential approach,the MAI-PbI2-MAI precursor film with a typical sandwich structure formed a uniform and pinhole-free perovskite film without any PbI2 residue,which could significantly improve the performance of the devices.Moreover,the bottom MAI layer of the MAI-PbI2-MAI precursor film could improve the interfacial contact of porous TiO2 layer,leading to promoting the charge transfer and reducing the recombination rate.Therefore,the devices fabricated by the sandwich structure MAI-PbI2-MAI precursor films showed dramatic improvements of open-circuit voltage(Voc),short-circuit current density(Jsc),fill factor(FF)and PCE.As a result,a promising PCE of 17.8%with a good long-term air stability were achieved for the MAI-PbI2-MAI precursor film based PSC,which are better than that prepared by sequential approach.For different structure of the PSCs(planar structure PSCs and mesoscopic structure PSCs),the requirements for the quality of perovskite photoactive films are different.In this paper,the requirements of the perovskite film prepared by sequential deposition method for planar PSCs and mesoscopic PSCs were systematically studied,and the reason and mechanism were analyzed in detail.Based on these mechanisms,we developed a new method for the preparation of high efficient and stable planar PSCs by sequential deposition method.