Towards Efficient And Stable All-inorganic Perovskite Solar Cells

All-inorganic halide perovskites have gained increased research interest in the perovskite community for its excellent thermal stability and higher crystallinity compared to organic-inorganic hybrid perovskite materials.Especially for all-inorganic perovskite solar cells,within a few years'developments,the device performance is comparable to organic-inorganic hybrid perovskite devices.For all-inorganic perovskite solar cells,the most urgent thing now is to further improve power conversion efficiency and lifetime.And interface and composition engineering methods play an important role in tackling these two challenges.Thus,this thesis devotes to improving the performance and stability of all-inorganic perovskite solar cells via interface engineering and composition engineering,aiming to provide theoretical and practical guidance for the realization of low-cost,efficient and stable all-inorganic perovskite photovoltaic devices and their large-scale commercial applications in the future.First of all,in chapter I,we mainly introduce the research background and crystal structure of all-inorganic perovskite materials,as well as the development process of its photovoltaic devices.So far,researchers have developed numerous strategies to improve the efficiency and stability of all-inorganic Cs Pb X₃ perovskite solar cells,but there is still plenty of room for further improvement in this area.In chapter II,a synergic interface design is demonstrated for photostable all-inorganic mixed-halide perovskite solar cells by applying an amino-functionalized polymer?PN4N?as cathode interlayer and a dopant-free hole-transporting polymer?PDCBT?as anode interlayer.First,the interfacial dipole formed at the cathode interface reduces the work function of Sn O₂,while PDCBT with deeper-lying highest occupied molecular orbital level provides a better energy-level matching at the anode,leading to a significant enhancement in open-circuit voltage.Second,the PN4N layer can also tune the surface wetting property to promote the growth of high-quality perovskite films with larger grain size and higher crystallinity.Most importantly,both theoretical and experimental results reveal that PN4N and PDCBT can interact strongly with the perovskite crystal,which effectively passivates the electronic surface trap states and suppresses the photoinduced halide segregation of Cs Pb I₂Br films.Therefore,the optimized Cs Pb I₂Br devices exhibit reduced interfacial recombination with efficiency over 16%,which is one of the highest efficiencies reported for all-inorganic perovskite solar cells.A high photostability with only 8%efficiency drop is demonstrated for the Cs Pb I₂Br devices with dual interfacial modifications under continuous 1 sun equivalent illumination for 400 hours.In chapter III,we have adopted two novel polymers?PSQ1 and PSQ2?as the dopant-free hole-transporting materials of all-inorganic perovskite solar cells,which are synthesized by the research group of Prof.Zhong'an Li at Huazhong University of Science and Technology.Two polymers not only show high hole mobilities and suitable energy levels,but also achieve comprehensive passivation effect on Cs Pb I₂Br perovskite.The fabricated Cs Pb I₂Br devices based on PSQ2 hole-transporting layer can deliver an impressive power conversion efficiency of 15.5%,outperforming those of the doped Spiro-OMe TAD devices?14.4%?.In addition to the improved efficiency,more importantly,the photostability of optimized PSQ2-based devices can maintain 83%of its initial efficiency under continuous 1 sun equivalent illumination for300 hours.In chapter IV,we report a facile approach to simultaneously enhance both the efficiency and long-term stability for the Cs Pb I_2.5Br_0.5 solar cells via inducing excess Pb I₂ into the precursors.Comprehensive film and device characterizations were conducted to study the influences of different amount of Pb I₂ on the crystal quality,passivation effect,charge dynamics and photovoltaic performance.It is found that excess Pb I₂ is beneficial for improving the device efficiency and operation stability.The excess Pb I₂ in the precursor solution can facilitate the formation of all-inorganic perovskite films with increased crystallinity and reduced trap density,which guarantees the film with reduced charge recombination and increased charge mobility,The residual Pb I₂ at the grain boundaries also provides a passivation effect,which improves the optoelectronic properties and charge collection property in optimized devices,leading to a power conversion efficiency up to 17.1%with a high open-circuit voltage of 1.25 V,which is one of the best efficiencies reported for all-inorganic perovskite solar cells to date.More importantly,a remarkable long-term operational stability is also achieved for the optimized Cs Pb I_2.5Br_0.5 solar cells,retaining 76%of their initial efficiency after continuous power output at the maximum power point for 420 hours.Finally,we have completely summarized the innovative achievements achieved by using interface and composition engineering strategies in this thesis.These discoveries can have a positive role in promoting the development of all-inorganic perovskite photovoltaic cells and even organic-inorganic hybrid perovskite photovoltaic cells.