Study On Fabrication And Charge Loss Mechanism Of High Performance Perovskite Photoelectric Devices

Organic-inorganic hybrid perovskite materials have shown outstanding development value in the fields of light emission,laser,photodetection,and photovoltaic due to their excellent photoelectric properties.The performance of perovskite devices mainly depends on crystalling quality of perovskite active layers.Therefore,improving the crystal quality of perovskite materials and exploring new high-performance perovskite materials have become the key issues which affect the development of perovskite devices.During the device optimizing process,the physical mechanism such as charge dynamics and charge loss mechanism inside the device have gradually become the focus of researchers because they can guide the optimization direction of the device.The work of this thesis focuses on improving the crystalline quality of perovskite materials,developing new perovskite materials,and exploring the internal working mechanism of devices,and has achieved the following results:Firstly,a universal method for preparing high-quality perovskite materials was developed:we improved the crystalline quality of perovskite materials by employing Pb-O interface interactions with the introduction of surface-oxygen-rich insulating oxide substrates(e.g.hydrolytic Al2O3 and SiO2).This method is universal for both the perovskite poly crystalline and single crystals with different components.A much longer carrier diffusion length of exceeding 5 ?m together with significantly reduced trap density and non-radiative recombination of the perovskite film has been achieved.And these perovskite films show much better lasing and photodetector performance,indicating promising applications for the light emitting,lasing and detector devices.Secondly,we have discovered an interesting self nano phase-segregation phenomenon in thiocyanate(SCN)anion layered perovskite(e.g.Cs2Pb(SCN)212).New charge transfer channels in nano CsPbI3 phase between inorganic layers have been found,which can efficiently accelerate interlayer charge transfer process in 2D SCN perovskite.We demonstrate that the SCN anion layered perovskite is a more alluring 2D material system for optoelectronic applications by studying their photovoltaic and photodetection properties.A high photoelectric conversion efficiency of 4.24%has been achieved from the Cs2Pb(SCN)2I2 based planar solar cell,which is several times as high as that of previously reported pure long-cation 2D perovskite device.For the photodetection application,compared to the conventional cation layered perovskite and even the 3D perovskite,the polycrystalline Cs2Pb(SCN)2I2 lateral-structured device exhibits a much higher photodetection capability,a faster response velocity,higher bandwidth up to 105 Hz and superior photoelectric stability.Impressive polarization sensitivity within this polycrystalline device has also been found.These outstanding photoelectric characteristics provide huge promise of applicating anionic 2D perovskite material system for efficient optoelectronic devices.Thirdly,we explored the application potential of SCN materials in the field of light emission.We have realized overcoming the luminescence limit of the SCN-based layered perovskite(e.g.MA2Pb(SCN)2I2)by introducing and controlling nano phase structures within the 2D framework.We find that low-concentration nano-scale emission centers arisen from phase segregation can spontaneously exist within this perovskite system.These low-bandgap centers exhibit a quantum-well emission behavior and possess a high second-order radiative recombination rate.Furthermore,internal stress induced from nanostructured substrates is introduced to enhance the degree of phase segregation for luminescence improvement.The high luminescence performances achieved here demonstrate that the anion layered perovskite system can also be a lucrative candidate for light-emitting devices through phase controls within the nano scale.Finally,we propose a new analysis methodology to quantitatively extract charge dynamics properties and charge loss mechanism of photovoltaic devices from the electrical transients,such as charge extraction and collection quantum efficiency and the density of defects within the absorber.This methodology has been successfully applied to study conventional silicon and emerging kesterite and perovskite solar cells herein and is able to extend to other photovoltaic device systems with similar structures.Therefore,this work provides an alluring route for comprehensive investigation of dynamic physics processes and charge loss mechanism of junction solar cells and possesses potential applications for other optoelectronic devices.