Study of hybrid perovskite based thin films for field effect transistor and UV photodiode applications / Yashotha Subramaniam

Yashotha , Subramaniam (2023) Study of hybrid perovskite based thin films for field effect transistor and UV photodiode applications / Yashotha Subramaniam. PhD thesis, Universiti Malaya.

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Abstract

Recent developments in the field of electronics involving three-dimensional (3D) organic-inorganic hybrid perovskites have sparked the discovery of two-dimensional (2D) and one-dimensional (1D) materials. The introduction of bigger organic amine groups into the perovskite structure results in low-dimensional perovskites having enormous potential for creating high-stability perovskite photovoltaics and optoelectronics. The morphology issues greatly limit charge transport in the thin film. Primarily, this study uses solution processing techniques to investigate the potential application of low dimensional perovskite as an active layer in field-effect transistors (FET). Adding Nafion as a surface modification to the top of the indium tin oxide (ITO) electrode has demonstrated that charge injection can be improved. A thin layer of spin-coated Nafion deposited between the ITO and the perovskite active layer reduces the injection barrier by altering the ITO's effective work function from 4.40 eV to 4.90 eV. Subsequently, poly (9-vinylcarbazole) PVK blended into a one-dimensional Propylammonium lead bromide (PAPbBr3) precursor solution. The blended PVK induced preferential vertically orientated nanopillars as revealed by synchrotron-based two-dimensional grazing incident X-ray diffraction. This simultaneously reduced the grain boundaries and improved pin-hole free films. As a result, maximum hole mobility of 0.012 cm2/Vs was achieved. Additionally, it was discovered that adding PVK to pristine PAPbBr3 reduced the hysteresis voltage from 4V to 0.95 V (in PAPbBr3: the PVK-25% device). This research indicated that the performance of FETs depends on the injection barrier and the perovskite nanopillar microstructure. The next phase of this thesis assessed the applicability of low-dimensional perovskite, 2D layered phenethylammonium lead bromide (PEA2PbBr4) as an active layer in a self-powered ultra-violet (UV) photodiode. The PEDOT: PSS was chosen to serve as the hole transport layer, while the PCBM material was chosen as the electron transporting hole blocking layer. The moisture-sensitive PEDOT: PSS, on the other hand, led to inadequate surface coverage and the deterioration of perovskite material. This, in turn, led to a decrease in the device's performance and instability. A significant increase in photocurrent and stability was observed when a hydrophobic Nafion layer was added on top of the PEDOT: PSS and perovskite interface. At 0 V bias, the best PEA2PbBr4 film-based device had a high photocurrent of 0.34 mA/cm2 and a fast response time of 15.6 μs. The improved device's responsivity and detectivity were estimated to be 25 mA/W and 2.54x1011 Jones, respectively. Field-emission scanning electron microscopy and energy dispersive x-ray spectroscopy have proven that the increased surface coverage is directly responsible for better device performance. Moreover, owing to the hydrophobic nature of the Nafion layer, the PEA2PbBr4 films and devices based on Nafion-coated PEDOT: PSS exhibited superior UV light stability than those without the Nafion layer. Thus, high-performing devices were successfully fabricated using highly repeatable, solution-processed, and cost-effective methods.

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