Study On Perovskite Solar Cell Of Inorganic Oxide Charge Transporting Layers Based On Low Temperature TiO₂

Organic-inorganic hybrid perovskite solar cells have attracted wide attention due to the advantages of high power conversion efficiency(PCE),simple preparation process and low cost.Electron transport materials in perovskite solar cell(PSC)played an important role in conducting electrons to external circuits and blocking the passage of holes.In order to improve the stability of PSC and further reduce the cost of devices,it was necessary to replace organic small molecule or polymer carrier conductive layer materials with inorganic metal oxides,which were easy to cause degradation of active layer of devices.Because the bottom position of the conduction band of titanium dioxide matching the lowest molecular orbital energy level of perovskite crystals,it was favorable for the injection of electron,and its wide band gap characteristics could effectively block the holes injection in perovskite.Moreover,due to the various synthesis methods,simple preparation process,the stable chemical property,environment friendly and the high electron mobility of TiO₂,it has great potential as an electron transport material in perovskite solar cell,especially in the construction of PSC with all inorganic conductive layers.Developing the technology of low-temperature and suitable for all inorganic conductive layer PSC was of great significance.It was not only to improve the stability of PSC and reduce device costs,but also to guide the development of electron transport layers(ETL)of other perovskite optoelectronic devices.This paper focused on the synthesis of titanium dioxide film at low temperature and the titanium dioxide film was applied in PSC with all inorganic conductive layers gradually.By optimizing the process of nanocrystalline and nanocrystalline films of titanium dioxide in traditional positive PSC,the low-temperature preparation of electron transport layer of titanium dioxide nanocrystalline films with high PCE PSC was realized.Then introducing the low-temperature preparation process of titanium dioxide nanocrystalline films into PSC with all-inorganic conductive layers to construct inverted structure PSC,the low-temperature and anhydrous atmosphere of titanium dioxide ETL was realized.The construction of stable and low-cost PSC with all-inorganic conductive layers was preliminarily solved by uniform film formation.The surface and interface of titanium dioxide conductive layer were further modified,which significantly improved the photoelectric performance and stability of PSC with all-inorganic conductive layers and obtained PSC with both stable,high efficiency and low cost.Specific research contents are as follows:(1)Using FTO as the substrate,the methods of TiCl₄ water chemical bath hydrolysis,TiCl₄hydrothermal alcoholysis and TTIP hydrolysis were used to prepare the titanium dioxide ETL at low temperature and the PSC of the structure of FTO/TiO₂/MAPb I₃/Spiro-OMe TAD/Au was assembled,its photoelectric properties were investigated,too.The results showed that the PSC assembled by TiCl₄ hydrolysis method has the best photoelectric properties:open circuit voltage(V_oc)was 1.04 V,short circuit current density(J_sc)was 21.07 m A/cm²,filling factor(FF)was 70.59%,and photoelectric conversion efficiency was 15.45%.Furthermore,by controlling the concentration of TiCl₄ precursor solution,the morphology and crystal phase of titanium dioxide ETL prepared at low temperature were effectively controlled,thus the carrier conduction of ETL was regulated,and the photoelectric performance of the PSC was optimized.When the concentration of TiCl₄ precursor solution was 270 m M,the titanium dioxide film has rutile-anatase mixed crystal phase.Many bumps were formed on the surface of dense titanium dioxide films.The existence of bumps was conducive to the adhesion of perovskite film,and has strengthened the contact with perovskite film.The assembled PSC has the best PCE of16.72%,V_oc of 1.01 V,J_sc of 22.45 m A/cm² and FF of 73.42%.(2)The application of titanium dioxide prepared by hydrolysis of TiCl₄ in inverted structure PSC with inorganic conductive layers may result in degradation of perovskite active layer,and the dispersion and uniformity of granular films were poor.So using the same precursor and relacing water with alcohol,anatase titanium dioxide nanocrystals with good dispersibility and crystallinity were synthesized by alcoholysis of TiCl4 with low temperature solution strategy.Then titanium dioxide nanocrystals were dispersed in different solvents and spin-coated on perovskite films to realize the construction and assembly of inverted structure PSC with inorganic oxide conducting layer.Through the selection of solvents and concentration optimization of nanocrystalline dispersing solution,it was found that the PSC with the structure of ITO/Ni O_x/MAPb I₃/TiO₂/Ag had the best photoelectric conversion efficiency of 6.91%with ethanol as dispersing solvent and the concentration of 5 mg/ml.(3)In order to optimize the photoelectric performance and stability of inverted structure PSC with inorganic oxide conduction layer,the surface morphology of titanium dioxide thin films and their contact with metal electrodes,as well as the inhibition of carrier recombination at the interface of electronic conduction layer were studied.By inserting a SnO₂ layer between perovskite layer and titanium dioxide layer,the direct interface between electronic conduction layer and perovskite layer was improved and the PCE increased from 6.91%to 9.35%.In order to eliminate Schottky barrier at the interface,a layer of BCP was inserted between titanium dioxide and Ag counter electrode based on the SnO₂ modified titanium dioxide interface,which reduced the charge accumulation at the titanium dioxide/Ag interface,increased the photoelectric conversion efficiency of PSC to 9.95%,and improved the stability.