In this study, nanostructure engineering of halide perovskite (HP) is demonstrated as a strategy to develop high-performance optoelectronic devices. Motivated by conventional nanoimprinting lithography (NIL), which has been utilized for tuning electronic properties of organic materials, HP film is p...
In this study, nanostructure engineering of halide perovskite (HP) is demonstrated as a strategy to develop high-performance optoelectronic devices. Motivated by conventional nanoimprinting lithography (NIL), which has been utilized for tuning electronic properties of organic materials, HP film is pressurized with nanopatterned polymeric mold during crystallization. The induced pressure affects
optical/electronic/crystallographic properties of HP as well as surface structure. This research consists of three main chapters.
In chapter 2, high-performance HP nanopillar photodetector is demonstrated. Numerous studies have reported the use of halide perovskites as highly functional light-harvesting materials. The development of optimized compositions and deposition approaches has led to impressive improvements; however, no noticeable breakthrough in performance has been observed for these materials recently. Here, a breakthrough that enables the fabrication of vertically grown halide perovskite (VGHP) nanopillar photodetectors via a nanoimprinting crystallization technique is demonstrated. We used engraved nanopatterned polymer stamps to form VGHP nanopillars during the pressurized crystallization of the softly baked gel state of a methylammonium lead iodide (CH3NH3PbI3, denoted MAPI or MAPbI3) film. The VGHP films exhibit much lower defect density and higher conductivity, as supported by current-voltage (I-V) characteristic measurements and conductive atomic force microscopy (c-AFM) measurements. Ultimately, two-terminal lateral photodetectors based on the VGHP nanopillar films show a greatly enhanced photoresponse compared with flat film-based photodetectors. We expect that the deposition method presented here will help
surpass the technical limits and contribute to further improvements in various halide perovskite-based devices.
In chapter 3, the grain boundary healing effect of nanopatterned HP is suggested. Although organic-inorganic HP-based photovoltaics have high photoconversion efficiency (PCE), their poor humidity stability prevents commercialization. To overcome this critical hurdle, focusing on the grain boundary (GB) of HPs, which is the main humidity penetration channel, is crucial. Herein, pressure-induced crystallization of HP films prepared with controlled mold geometries is demonstrated as a GB-healing technique to obtain high moisture stability. When exposed to 85% RH at 30 ℃, HP films fabricated by pressure-induced crystallization have enhanced moisture stability due to the enlarged HP grain size and low-angle GBs. The crystallographic and optical
properties indicate the effect of applying pressure onto HP films in terms of moisture stability. The photovoltaic devices with pressure-induced crystallization exhibited dramatically stabilized performance and sustained over 0.95 normalized PCE after 200 h at 40% RH and 30 ℃.
In chapter 4, we reveal the effect of induced pressure during crystallization of HP onto charge carrier dynamics. Traditionally, the trap-assisted photomultiplication (PM) of photodetectors has been accomplished by employing a charge injection channel. In this work, trap-assisted PM of HP is achieved by a pressure-induced crystallization process without any charge injecting materials. By pressurizing precrystallized HP during crystallization, its crystallographic property is strongly modified by compressive strain as well as tailored morphology. Additionally, the process temperature is greatly reduced below 100 ℃, which is far below the crystallization temperature of α-FAPbI3 (150 ℃), allowing for flexible device fabrication. With the process, the photoresponse of the photodetector dramatically increases under weak light intensity (100% external quantum efficiency (EQE). To clarify this PM mechanism, we suggest a trap-assisted PM model under photoconductive conditions supported by photoluminescence (PL) spectroscopic techniques. Additionally, the process enables improvements in air stability, bending stability and photostability against
the respective stresses.
In this study, nanostructure engineering of halide perovskite (HP) is demonstrated as a strategy to develop high-performance optoelectronic devices. Motivated by conventional nanoimprinting lithography (NIL), which has been utilized for tuning electronic properties of organic materials, HP film is pressurized with nanopatterned polymeric mold during crystallization. The induced pressure affects
optical/electronic/crystallographic properties of HP as well as surface structure. This research consists of three main chapters.
In chapter 2, high-performance HP nanopillar photodetector is demonstrated. Numerous studies have reported the use of halide perovskites as highly functional light-harvesting materials. The development of optimized compositions and deposition approaches has led to impressive improvements; however, no noticeable breakthrough in performance has been observed for these materials recently. Here, a breakthrough that enables the fabrication of vertically grown halide perovskite (VGHP) nanopillar photodetectors via a nanoimprinting crystallization technique is demonstrated. We used engraved nanopatterned polymer stamps to form VGHP nanopillars during the pressurized crystallization of the softly baked gel state of a methylammonium lead iodide (CH3NH3PbI3, denoted MAPI or MAPbI3) film. The VGHP films exhibit much lower defect density and higher conductivity, as supported by current-voltage (I-V) characteristic measurements and conductive atomic force microscopy (c-AFM) measurements. Ultimately, two-terminal lateral photodetectors based on the VGHP nanopillar films show a greatly enhanced photoresponse compared with flat film-based photodetectors. We expect that the deposition method presented here will help
surpass the technical limits and contribute to further improvements in various halide perovskite-based devices.
In chapter 3, the grain boundary healing effect of nanopatterned HP is suggested. Although organic-inorganic HP-based photovoltaics have high photoconversion efficiency (PCE), their poor humidity stability prevents commercialization. To overcome this critical hurdle, focusing on the grain boundary (GB) of HPs, which is the main humidity penetration channel, is crucial. Herein, pressure-induced crystallization of HP films prepared with controlled mold geometries is demonstrated as a GB-healing technique to obtain high moisture stability. When exposed to 85% RH at 30 ℃, HP films fabricated by pressure-induced crystallization have enhanced moisture stability due to the enlarged HP grain size and low-angle GBs. The crystallographic and optical
properties indicate the effect of applying pressure onto HP films in terms of moisture stability. The photovoltaic devices with pressure-induced crystallization exhibited dramatically stabilized performance and sustained over 0.95 normalized PCE after 200 h at 40% RH and 30 ℃.
In chapter 4, we reveal the effect of induced pressure during crystallization of HP onto charge carrier dynamics. Traditionally, the trap-assisted photomultiplication (PM) of photodetectors has been accomplished by employing a charge injection channel. In this work, trap-assisted PM of HP is achieved by a pressure-induced crystallization process without any charge injecting materials. By pressurizing precrystallized HP during crystallization, its crystallographic property is strongly modified by compressive strain as well as tailored morphology. Additionally, the process temperature is greatly reduced below 100 ℃, which is far below the crystallization temperature of α-FAPbI3 (150 ℃), allowing for flexible device fabrication. With the process, the photoresponse of the photodetector dramatically increases under weak light intensity (100% external quantum efficiency (EQE). To clarify this PM mechanism, we suggest a trap-assisted PM model under photoconductive conditions supported by photoluminescence (PL) spectroscopic techniques. Additionally, the process enables improvements in air stability, bending stability and photostability against
the respective stresses.
주제어
#Halide perovskites Nanostructure engineering Nanoimprinting lithography Photovoltaics Photodetectors Optoelectronic devices
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