Study On Photovoltaic Performance Improvement Of Plane Heterojunction Perovskite Solar Cells By Transition Metal Oxide(Sulfides) Compound

Owing to its high photoelectric conversion efficiency（PCE）and low production cost,perovskite solar cells（PSCs）have became the frontier direction of photovoltaic research.With its PCE up to 25.5%in 2021,PSCs have emerged as the most promising candidate for replacing silicon solar cells.However,there is still a lot of room for improvement from the theoretical limit efficiency of its PCE of 33.5%.The PCE of solar cells mainly depends on the light capture efficiency and carrier separation efficiency of critical functional materials.Designing and preparing high-quality perovskite light absorbing layer,charge transport layer and optimizing key interfaces have become effective means to improve the photovoltaic performance of PSCs.Therefore,it is of great research value and significance to find a new material system that could optimize the quality of each functional layer,broaden the spectral range and optimize the interface performance,reveal the interaction between material properties,functional layer performance and photovoltaic device performance,thus finally obtain PSCs with excellent performance.Among many organic/inorganic materials,transition metal oxide（sulfides）semiconductor materials have been widely used in various photoelectric devices due to their excellent photoelectric performance,low cost and great stability.In this thesis,taking MAPb I₃-based PSCs as the research object,we focus on using transition metal oxide（sulfur）material to optimize the perovskite layer,ETL,light utilization rate and interface properties within devices to reveal the influence of specific material,introduction technique and addition amount on the photovoltaic performance of PSCs,and finally elucidate the related physical mechanism.The main research contents are as follows:（1）In order to optimize the conductivity and energy level structure of electron transport layer,a novel slight amount of cadmium sulfide quantum dots（CdS QDs）-assisted SnO₂ETL has been developed with low-temperature fabrication process.The slight addition of CdS QDs not only improves the crystallinity and flatness of SnO₂ETLs to provide a promising workstation to obtain high-quality perovskite absorption layers,but also increases the conductivity of SnO₂ETL by an order of magnitude,and regulates the energy level matching between SnO₂ETL and perovskite.These outstanding properties greatly accelerate the extraction and transfer of charge in the PSCs.Thus,the MAPb I₃-based PSCs with a slight amount of CdS QDs-assisted SnO₂as the ETL achieve a maximum PCE of 20.78%with better stability of devices in air.These results not only prove the importance and potential of semiconductor QDs modification on ETLs,but also pave the way for developing such composite ETLs for further enhancing the photovoltaic performance of planar PSCs.（2）In order to improve the light utilization rate and charge transfer efficiency of PSCs,the nonstoichiometric WO_3-Xnanorods（NRs）were synthesized by solvothermal method,and their LSPR effect was regulated by sintering at different temperatures under nitrogen atmosphere.When the calcination temperature was 600℃,the LSPR effect of WO_3-XNRs was the strongest.Subsequently,the WO_3-XNRs sintered at 600℃was introduced into perovskite and the interface between perovskite and hole transport layers（HTLs）by anti-solvent method.The LSPR effect of WO_3-XNRs expands the spectral absorption range and significantly increases the photocurrent of the device.The near-field enhancement of local electromagnetic field caused by LSPR effect can effectively promote the charge transfer at the perovskite/HTLs interface.Therefore,the introduction of WO_3-XNRs synchronously optimizes the optical and electrical properties in the device amd leads to a PCE of 21.14%in MAPb I₃-based PSCs.These results not only elucidates the related mechanism of inorganic oxide semiconductor with LSPR effect to enhance the performance of PSCs,but also provides an effective technical scheme for improving the photovoltaic performance of PSCs.（3）In order to stabilize the LSPR effect of WO_3-XNRs and further passivate the internal defects of perovskite,CdS QDs were grown on the surface of WO_3-XNRs by in-situ growth method to construct WO_3-X@Cd S heterojunction with LSPR effect.Such heterojunctions with different CdS QDs content were introduced into the perovskite and the interface between perovskite and HTLs by anti-solvent method.Taking advantages of each component,we can not only improve the light utilization of the device,but also promote the uniform nucleation of perovskite and reduce the density of defect states in the film and at the interface.The energy level barrier between perovskite and HTLs is reduced to a certain extent,so that the interfacial recombination is inhibited,and the interfacial charge transfer is accelerated.Finally,the PCE of MAPb I₃-based PSCs is improved to 21.49%.The results innovatively used the oxide heterojunction with LSPR effect to improve the photovoltaic performance of PSCs,which provides a new concept for the design of new additive materials.