Evaluation of Nanoscale Hybrid Perovskite Photovoltaic Properties via Scanning Probe Microscopy

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GHAIDA SAEED ALOSAIMI
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Saudi Digital Library
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Perovskite-based photovoltaic (PV) devices are promising candidates for next-generation PV applications. However, defects that cause poor stability in hybrid perovskites create a manufacturing bottleneck. Recently, grain boundary (GBs) defects have shown dual impacts: detrimental or benign. Therefore, exploring nanoscale charge dynamics will allow us to understand these defects' physical properties to optimize device performance and long-term stability. Scanning probe microscopy (SPM) is an effective instrument for studying micro- and nano-sized structures and electronic properties. This thesis used SPM to study the photoelectric properties of three-dimensional (3D) and quasi-two-dimensional (2D) halide perovskite. Morphology-dependent charge transport is investigated with a new approach using directional illumination and SPM characterization. The nanoscale optoelectronic behaviour of 3D caesium formamidinium lead iodide (FAPbI3) and methylammonium lead bromide (MAPbBr3) with various electron transport layers (ETLs); (SnO2), (c-TiO2), and phenyl-C61-butyric acid methyl ester (PCBM)/SnO2, under indoor light is explored. The implications of perovskite GB defects and perovskite/ETL interfacial defects on the charge transport properties are identified by varying illumination direction and wavelength. The findings demonstrate that the interface and GB defects dominate device performance under indoor lighting conditions. Perovskite/SnO2 is recommended as an efficient indoor PV device. The nanoscale electronic effects of triplet state management in quasi-2D FAPbBr3 is studied. The photoelectrical properties are investigated under laser illumination and bias application. The findings indicate that the quasi-2D perovskite with naphthyl methyl ammonium (NMA+) mitigates the ion migration and enhances the charge transport through GBs. SPM results offer new insight into the physical properties of defects in layered quasi-2D perovskite for optimizing device performance. Moisture-dependent SPM characterizations are performed on open and compressed GB structures of wide bandgap (FAPbI3)0.3(FAPbBr3)0.7 perovskites. The structural and surface electrical properties are examined. The findings demonstrate that the compact-GB sample has a higher photocurrent, lower current hysteresis, and lower trap states under 60% relative humidity for 24 hours than the open-GB sample. Therefore, controlling GB structure and humidity level enhances a material’s optoelectronic properties. The SPM results shed light on microscopic observations of perovskite (PV) devices to optimize efficiency and long-term stability.
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