Study Of Electron Transfer Layers And Interfaces In Perovskite Solar Cells

Perovskite solar cells?PSCs?have attracted widely interest due to their excellent light-absorb ability,facile fabrication process and high power conversion efficiency,supposing to have protential application in the next generation of photovoltaic industry.In this device,electron transfer layer?ETL?and heterojunction interfaces play an important role in the charge transfer and recombination processes,significantly affecting the performance of perovskite solar cells.In this thesis,we study the electron transfer layer and interface in the device,including the accurent measurement of PSCs,new type of double structure of ETL,atomic structure investigation of ETL/perovskite interface and the design of atomic layer deposition system for ETL fabrication.The main research contents are summarized as follows:Firstly,we studied the influence of different mask apertures on the open-circuit voltage measurement of perovskite solar cells.Aperture masks with different sizes were equipped to control the proportion of dark-state region.Statistical results of photovoltaic parameters,ideality factor,and reverse saturation current density revealed that different mask apertures would affect the J-V measurement results,especially the open-circuit voltage.A double diode model simulation together with the impedance spectroscopy and transient photovoltage decay measurement has been furthere employed and found that the mask with inappropriate shading,which is smaller than the cells active area,will introduce excess charge transfer and recombination pathways,thus lead to an underestimate of open-circuit voltage.This work provides a promising route towards a more accurate J-V measurement of perovskite solar cells.Secondly,a TiO₂/ZnO electron transport bilayer,which combines the advantages of high electron extraction and low interfacial recombination together,has been designed for planar perovskite solar cells.With this bilayer,the front surface recombination in the cell is significantly suppressed,and a high efficiency exceeding 17% has been achieved.These results suggest a promising and simple approach to further design photovoltaic devices from the aspect of charge transport and recombination.Thirdly,we examined a TiO₂/CH₃NH₃PbI₃ interface and found that a heavy atomic layer exists in such interfaces,which is attributed to the vacancies of methylammonium?MA?cation groups.Further,first-principles calculation results suggested that an MA cation-deficient surface structure is beneficial for a strong heterogeneous binding between TiO₂ and CH₃NH₃PbI₃ to enhance the interface stability.Our research is helpful for further understanding the detailed interface atom arrangements and provides references for interfacial modification in perovskite solar cells.Finally,we designed an atomic layer deposition?ALD?system,including vaccum chamber,gas line,electrical control and automatic control program,which exhibit fast response performance.This system has been applied in the thin film fabrication and interface modification in solar cells.In particular,this ALD has sucessfuly deposited ZnO and TiO₂ as ETL in perovskite solar cell,achieving more than 18% power conversion efficiency.