Interface Engineering Study On High Efficiency And Stability Of Inverted Perovskite Solar Cells

After more than a decade of rapid development,the highest certification efficiency of single-junction perovskite solar cell(PSC)has skyrocketed to 25.7%,which is comparable to traditional monocrystalline silicon solar cells.At the same time,it has great potential for industrialization due to the simple process and low-cost.However,many problems such as poor stability limite large-scale commercial application.In this thesis,we choose inverted p-i-n PSCs as our research object.The a series of interface engineering strategies including stable Bi-based double-layer metal electrode system,defect passivation strategy of buried interface,and defect passivation of the perovskite surface have adopted to improve PSCs’ efficiency and stability to meet the requirements of commercial application.The main contents are described as follows:(1)Aiming at the problem of traditional electrode penetration and being corroded,a chemical inert semi-metallic bismuth-based stable electrode system was developed to improve the operation stability of the device.Half-filled 6P orbital of Bismuth makes it relatively stable in chemical properties.This semi-metallic bismuth has a unique halogen corrosion resistance(<150 °C).The results have confirmed that bismuth could contact with halide perovskites directly without chemical corrosion.In addition,the semi-metallic bismuth film deposited at low temperature has high crystallinity,grows in a twodimensional laminar shape with fewer grain boundaries and has a dense morphology.The introduction of a bismuth interface layer into the device structure,which could not only prevent the perovskite active layer from being exposed to external moisture,but also protect the metal electrode from corrosion by iodide ions in the perovskite active layer.Bismuth interfacial layer could be prepared by low-temperature and cheap thermal evaporation,without increasing the complexity of process preparation and the cost when scaling-up production.Bismuth-interface based devices have greatly improved stability when subjected to humidity,heat and light stress.The unencapsulated devices maintained88% of their initial efficiency over 6000 h in the dark environment.The devices retained95% and 97% of its initial efficiency respectively when dark thermal aging at 85 ℃ and maximum power point(MPP)continuous light aging for 500 h.(2)In order to solve the problem of high voltage loss of inverted PSC,lewis base pyridine functional group was introduced into the molecular framework of polymer hole transport material PTAA,and the organic hole transport layer p-PY with defect passivating ability was designed and synthesized.Moreover,the pyridine functional group could effectively reduce its highest occupied molecular orbital(HOMO)energy level,and form a better energy level match well with FACs perovskite,reduce the interface energy loss,and greatly improve the device open-circuit voltage.The corresponding FACs PSC achieved 22.3% certified efficiency.FACs perovskite devices based on p-PY could resist high bias and have good long-term stability.The initial efficiency of FACs based PSCs remained 97.5% after 1 solar illumination aging 1000 h.After thermal aging at 85 ℃ for500 h and 120 ℃ for 200 h,the devices remained above 94% and 81%,respectively.(3)Aiming at the problem of increasing defects of perovskite thermal annealing,the passivation strategy of PEAI/PEABr mixed salt was adopted to further improve the device performance of FACs perovskite.On the one hand,the halogen vacancy defects in the perovskite are effectively reduced,on the other hand,the surface energy level arrangement of perovskite active layer could be adjusted,which is beneficial to charge extraction and separation,reducing the interface recombination between perovskite layer and electron transport layer(ETL).At last,the champion efficiency of prepared inverted PSC reached23.8%.In addition,the surface hydrophobicity of perovskite film after passivation based on mixed salt was significantly enhanced,which greatly improved the environmental stability.Therefore,the unencapsulated devices retained 95% of initial efficiency after 800 h exposure in a dark environment,while devices in a nitrogen atmosphere retained more than 97% of initial efficiency after 500 h exposure in 1 solar illumination.