Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Arash Takshi, Ph.D.

Committee Member

Ioanniss Kymissis, Ph.D.

Committee Member

Chris Ferekides, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Rasim Guldiken, Ph.D.

Committee Member

Xiaomei Jiang, Ph.D.

Keywords

Capillary Motion, Methylammonium Lead Iodide, Microfluidic, Photodetector, Piezoelectricity

Abstract

In recent years, there has been a significant interest in making electronic devices with low-cost techniques and materials for both industrial and medical applications. Methylammonium lead iodide perovskite (MAPbI3) is one of the novel materials which has drawn much attention owing to its outstanding optical and electrical properties along with inexpensive, simple, and easy fabrication methods. In this work, the feasibility of using microfluidic device fabrication techniques on making a perovskite phototransistor has been studied. The fabrication method well addresses challenges such as lead toxicity and instability.

In the first step, mechanical micromachining and laser engraving were employed to make two-terminal flexible perovskite photodetectors with an indium tin oxide (ITO)–MAPbI3–ITO horizontal structure. Photodetectors were made by filling engraved microchannels using the capillary motion of the solution containing the perovskite precursors. In addition to studying the photoelectric response of the devices with a solar simulator, potentiostat, and a Keithley source measure unit (SMU), the fabricated samples were characterized using scanning electron microscopy (SEM), X‐ray diffraction (XRD), and atomic force microscopy (AFM) methods.

Long term stability was observed when encapsulating the devices with either FluoroPel or CYTOP. Also, the effect of external normal and transverse forces on the photoelectric response of the devices were investigated, proving the piezotronic property of MAPbI3. In the highest state, when the normal force of 340 kPa was applied the photocurrent of the two-terminal photodetector increased by 97%. At this condition, the device exhibited a sensitivity (Iphoto/Idark) of 3250 with a photocurrent of ≈6.9 µA at 2.0 V bias and responsivity of 14.56 mA.W−1 under white light illumination of 80 mW.cm-2.

Finally, a perovskite phototransistor was fabricated following the optimized parameter of the laser ablation method to form the microchannel on an ITO coated polyethylene terephthalate (PET) substrate. The transistor characteristic proved the formation of a depletion-mode field-effect transistor (FET) with a conductive channel at 0 V gate-source voltage (Vgs) entering the saturation mode when the drain-source voltage (Vds) was above 10.0 V.

The proposed fabrication method is fairly simple and can contribute to the integration of perovskite photovoltaic devices with optofluidic circuit elements which may help in the further development of low-cost and disposable medical devices.

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