The bandgap tunability in methylammonium (MA) lead halide perovskites has motivated us to design a photoresistor array made of MAPbI3, MAPbBr1.5I1.5, and MAPbBr3. To pattern devices on the same substrate, a novel method of laser engraving the substrate was employed. In this method, first, an indium tin oxide (ITO) coated plastic substrate was laser engraved to make microchannels with a width of 50-100 µm. Capillary motion force was used to fill each channel with a different solution containing the perovskite precursors. The current-voltage characteristics of each sensor were studied under dark and light conditions. Light-emitting diodes with different wavelengths were used to study the response of each sensor to monochromic lights. The results are promising toward the fabrication of larger arrays of photosensors which potentially can be used for compact and integrated photospectrometers in lab-on-a-chip devices.
Increasing demand for low-cost devices has directed attention to developing simple methods for the deposition of solution-based semiconductors thin layers on various substrates. In recent years, 3D printing technologies have been known as a rapid, cost-effective technique for the deposition of a variety of materials. Here we employed pneumatic nozzle printing to make low-defect thin films of methylammonium lead iodide (MAPbI3) perovskite. The process parameters were optimized to control the crystallization condition. By using top-gate bottom-contact configuration, perovskite transistor on the silicon substrate was developed. The electrical properties of the fabricated transistor were measured under ambient light.
In the past few years, with the advance of laser technology, laser engraving has been considered as an alternative method to traditional lithography in the fabrication of microfluidic devices. Considering solution-based method as the main technique for perovskite deposition, the capillary motion of perovskite precursor can be employed for filling a laser-engraved patterned conducting layer. Herein, we used CO2 laser micromachining for the fabrication of the perovskite photodetector. First, several microchannels were formed by laser engraving of indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates. Power, speed and frequency parameters of the laser were varied in order to achieve the desired channel roughness. The samples were characterized by scanning electron microscope (SEM) and potentiostat. The I-V characteristics and bode plots of the sample showed a capacitive and an inductive behavior. Finally, a simulation tool was used to analyze the experimental data. This approach offers a simple, rapid and low-cost fabrication method for perovskite photodetector and can be used in large-scale commercial application.
The reaction center (RC) protein from photosynthetic purple bacteria is an organic structure with the capability of absorbing photons at low light intensities and generating electron-hole pairs with a high efficiency. Application of this biomaterial for energy harvesting and sensor devices has been studied before. A key in employing RCs in an electrochemical device is to immobilize the proteins on an electrode. In this work, ion-sensitive field-effect transistors with Si3N4 and TaO2 gate insulator were tested to measure the success rate in immobilizing the proteins. The results show that by far Si3N4 is a better choice than TaO2, due to the effective self-assembly of the linker molecules. The density of the attached proteins to the Si3N4 transistor was estimated to be 5×109 proteins/cm2 by analyzing the drift in the threshold voltage of the transistor. The fabricated device also presented the feasibility of using the RCs in an integrated photo-transistor.
Flexible sensors offer advantages such as light weight, cost effective, the potential to be manufactured with roll-to-roll equipment and to be used in portable and wearable devices. To remain as a cost-effective device, there is a need to reduce fabrication process expenses while preserving high sensitivity and responsivity. In this paper we demonstrate a novel method for facile fabrication of lead halide perovskite photosensor on a flexible substrate with high sensitivity. Capillary motion of perovskite precursor was employed as a convenient and simple technique to create a patterned layer of perovskite. Scanning electron microscope was employed to characterize fabricated perovskite layer. Fabricated layer was used in an ITO-perovskite-ITO structure to be used as a photosensor. Electrical and optical characteristics of the device have been investigated. The responsivity and the sensitivity of the device at 2.0 V were measured to be 0.1 A/W and 172, respectively. Finally, optical properties of the fabricated device were compared with another photodetector fabricated by conventional lithography process. The photocurrent of the sample, made by utilizing capillary motion, at 2.0 V was found to be 211 nA which was 2.8 times higher than the photocurrent of the sample made by traditional method (76 nA at 2.0 V). This novel method has shown great potential for commercial application.
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