Study On Preparation And Performance For The Efficient And Stable SnO₂-based Hybrid Perovskite Solar Cell

The organic-inorganic hybrid perovskite solar cells(PSCs)based on SnO₂electron transport layer(ETL)have rapidly become the research hotspot of the third generation solar cells,due to their excellent power conversion efficiency(PCE),low temperature preparation and low cost.At present,the certified PCE of PSCs based on SnO₂ ETL has reached 25.2%,which has exceeded the efficiency of the current commercial silicon-based solar cells.However,there are still many challenges for PSCs to commercial use.The most important are the preparation of high efficiency PSCs with large scale,device stability and improve repeatability of high efficiency PSCs.In order to improve the PCE and stability of PSCs,we aim at optimizing the structure,preparation process and electrical properities of ETL,improving the quality of perovskite film deposite on different conductive sudstrates(rigid and flexible)by two step method and interface engineering.Finally the stability and efficiencuy of PSCs prepared in the air environment have been all improved.The main research achievements are summarized as following:(1)When the SnO₂ ETL is prepared by spin-coating method,the water preatment process is introduced to increase the wettability of the conductive substrate and the spin-coating solution.The more compact SnO₂ films with less pinholes is prepared with water preatment.Then the Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45 perovskite is deposited on the optimized SnO₂ ETL by one-step spin-coating method.The SnO₂ETL/perovskite film show a more efficient charge extraction and transportation.Moreover,the defects in the perovskite layer are reduced,and the charge recombination in the interface between perovskite and SnO₂ film is well suppressed.Finally the optimized PSCs get a PCE of 19.6%.At the same time,when the devices without further packaged are stored in the air environment for 360 h,the PCE of the control device decrease by 30%,while the PCE of the optimized device decrease by10%,and show the long-term air stability of the device with water pre-treatment is significantly improved.(2)Due to the rapidly crystallize of PbI₂ film with moisture affection,the PbI₂ film prepared in a high-humidity air environment usually show a compact dendritic structure.The low-pressure assisted PbI₂ film is developed to prepare the PbI₂ film with a certain pinholes morphology,which is better for the large crystal of perovskite preparation.This provides a new method for the preparation of high-quality perovskite film in air environment.The defect state density of perovskite layer is effectively decreased,for that excessive PbI₂ content of the perovskite layer is reduced with low-pressure assisted PbI₂ film.Furthermore,the hysteresis effect of PSCs is significantly improved for that ion migration is effectively suppressed.Finally the PCE of optimized PSCs is increased from 10.78%to 20.34%.Moreover,to evaluate the stability of PSCs.The devices are placed in a dark drying oven with low humidity(?10%),and the devices in the optimized group could maintain 92%of their initial efficiency after 3600 h storage.However,the performance of the devices without low-voltage auxiliary treatment almost completely declined after 1000 h storage,indicating that the long-term stability of the devices are greatly improved.(3)In order to optimize the interface properties and improve the electron transport property of SnO₂ ETL,we introduced ammonia complexation into the SnO₂ colloidal nanoparticle solution,which significantly improved the conductivity of the SnO₂ film,and the electrons transportation between ETL and perovskite layer is enhanced.At the same time,the roughness of the SnO₂ film prepared by spin coating is increased,due to the nucleation and growth of SnO₂ is increased with the introduction of ammonia.When the perovskite layer deposite on SnO₂ film,the more roughness SnO₂ film would have a lower interface energy which can improve the growth of perovskite and formed a perovskite layer with less internal defects.The optimized PSCs have almost no hysteresis effect under forward and reverse scan test,and the device stability is also significantly improved.Finally the reverse(forward)PCE of PSCs base on ammonia complexation SnO₂ ETL with a small area(0.0736 cm²)is 20.53%(20.46%),and the reverse(forward)PCE of PSCs with an aperture area of 1cm² is 18.12%(18.07%).(4)A double layer ETL is prepared by introducing the ammonia complexed SnO₂colloidal nanoparticles on compact SnO₂ film and apply it to flexible PSCs.Due to the leakage current of PSCs is effectively suppressed and the quality of perovskite layer is improved,the PCE of flexible PSCs base on double layer ETL is improved.By optimizing the double layer ETL with different annealing temperatures,the double layer ETL with high tempeture(180?)annealed can get an improved electrical conductivity.Finally the best PCE of flexible PSCs is 18.08%with an aperture area of0.0736 cm² and 15.18%with an aperture area of 1cm².The bending of flexible PSCs prepared at different annealing temperatures is tested.The results show that the high temperature annealing do not cause physical damage to the flexible substrate,and the mechanical stability is not damaged.