Low-temperature Preparation Of TiO₂ And SnO₂ Electron Transport Layers And Atmospheres Application Of Perovskite Solar Cells

At present,organic-inorganic hybrid perovskite solar cells?PSCs?are considered as one of the most important developments in the field of solar cells.The power conversion efficiency?PCE?of PSCs has rapidly increased over the years,from the initial 3.8%to the current 22.1%.However,the vast majority of high-efficiency perovskite solar cells use mesostructures.Usually the mesostructure needs high-temperature sintering,the preparation process is cumbersome,and the manufacturing cost is increased.Therefore,in order to manufacture solar cells with high efficiency,first of all,some prerequisites should be fulfilled,such as low energy consumption,simple process flow and high photoelectric conversion efficiency.The method of treating the planar PSCs prepared by low-temperature solution can simplify the preparation process and reduce the manufacturing cost.In addition to high-quality perovskite films,excellent electronic transmission materials are also important for the improvement of the efficiency of PSCs.This dissertation focuses on the research of high-performance,low-energy electronic transmission materials.The main research contents and results are as follows:?1?The methodology of low-temperature solution-processed planar perovskite solar cells?PSCs?is desirable for achieving the aim.Although TiO₂ is the most widely used material in preparing electron-transporting layers?ETLs?of PSCs,it usually needs high-temperature sintering process to enhance electron mobility,which is not only energy consumption but also unsuitable for polymer based flexible substrates.Here,we propose a novel strategy to solve the problem.We use the sophisticated solvothermal method with the aid of oleic acid?OA?ligands to synthesize high aspect ratio and well crystalline TiO₂ nanorods.And then,ligand-exchange treatment is applied to substitute the insulating OA ligands with BF₄^-ions.These features are all advantageous for low-temperature solution-processed high-quality TiO₂ ETLs with highly electrical conductivity,fast electron extracting and transporting rates.As expected,the PSC with BF₄^--capped TiO₂ nanorod ETL achieves a high power conversion efficiency of 18.76%and good reproducibility.This work offers a feasible way to achieve high-efficiency low-temperature solution-processed planar PSCs.?2?Low-temperature solution-processed method is a kind of low-energy-consuming and simplemethodology for preparing cost-effective planar perovskite solar cells?PSCs?.A key factor affecting photovoltaic performance of planar PSCs is the quality of electron-transporting layers?ETLs?in the devices.Although TiO₂ is the most widely used material for preparing ETLs,it has drawbacks such as low electron mobility andultraviolet light induced photocatalysis.So the replacement of TiO₂ in ETLs is an important strategy to improve the stability and photovoltaic performance of PSCs.Here,the fabrication of high-performance planar PSCs based on low-temperature solution-processed well-crystalline SnO₂nanorods ETLs is reported.The sophisticated solvothermal method with the aid of oleic acid?OA?ligands is used to synthesizehigh aspect ratio and well crystalline SnO₂nanorods,and then,the OA-capped SnO₂nanorods are directly used to fabricate ETLs without complex treatments.The planar PSCs based on OA-capped SnO₂nanorods ETLs achieve a champion power conversion efficiency of 18.62%,which is much higher than that of the ones based on OA-capped TiO₂nanorods ETLs?14.27%?.Compared to the OA-capped TiO₂nanorods,the insulating OA ligands show weaker influence on the electronic properties of SnO₂ nanorods,owing to the high electron mobility character of SnO₂.?3?Due to the high electron mobility of SnO₂,PSCs based on OA-modified SnO₂NCs ETLs can achieve high performance.In order to further improve the photovoltaic performance of planar PSCs,SnO₂ NCs ETLs doped with Nb⁵⁺were used.Oxide-doped tin oxide?Nb-SnO₂?nanocrystals were synthesized by solvothermal method and used as ETL in PSCs.Through TEM and SEM tests,it can be seen that the Nb-SnO₂ nanocrystals are uniformly distributed,which is beneficial to the better contact between perovskite layer and electron transport layer interface.Due to the doping effect of Nb ions,the bandgap and high-band energy levels are amplified,the band gap of the electron transport layer is closer to the perovskite,and the electron recombination is reduced.The experimental results show that due to the doping of Nb ions,the conductivity is enhanced and the electron mobility is improved.The best PSCs based on Nb-doped SnO₂ NCs ETL achieve a power conversion efficiency of 20.07%,which is significantly higher than that of SnO₂ NCs ETL-based PSCs?18.64%?.