In this work, we report a lead-free hybrid halide perovskite system with a very high piezoelectric charge density for applications in nanogenerators. We use materials engineering by incorporation of formamidinium tin iodide, FASnI 3 , in a soft polymer (polyvinylidene fluoride, PVDF) matrix and demonstrate highperformance large-area flexible piezoelectric nanogenerators. This is achieved by using self-poled thin films of a FASnI 3 :PVDF nanocomposite. The fabricated devices show an output voltage up to ∼23 V and power density of 35.05 mW cm −2 across a 1 MΩ resistor, under a periodic vertical compression, with a release pressure of ∼0.1 MPa. Measured values of the local piezoelectric coefficient (d 33 ) of these films reach up to 73 pm/V. We provide the microscopic mechanism using first-principles calculations, which suggest that a soft elastic nature and soft polar optic phonons are responsible for the high piezoelectric response of FASnI 3 . Our studies open up a route to high-performance nanogenerators using a lead-free organic−inorganic halide perovskite family of materials.
Organic field effect transistors (OFETs) have been the focus of sensing application research over the last two decades. In comparison to their inorganic counterparts, OFETs have multiple advantages, such as low-cost manufacturing, large area coverage, flexibility and readily tunable electronic material properties. To date, various organic semiconductors (OSCs), both polymers and small molecules, have been extensively researched for the purpose of developing the active channel layers in OFETs, enhancing their sensitivity and selectivity. However, OFET devices still need to be optimized to demonstrate reliable performance at the device level and in sensing applications. This review begins with an introduction of the OFETs with an emphasis on their geometry, materials (OSCs), fabrication process, and data analysis. After this, multiple applications are discussed and the progress regarding sensing elements and precisions is highlighted. In the end, the challenges and possible future directions of OFET arrays in embedded sensing platforms are presented.
Organic
molecular monolayers (MoLs) have been used for improving the performance of various electronic device
structures. In this work, the concept of organic molecular surface
modification is applied for improving the performance of GaN-based
metal–semiconductor–metal (MSM) ultraviolet (UV) photodetectors
(PDs). Organic molecules of phenol-functionalized metallated porphyrin
(hydroxyl-phenyl-zinc-tetra-phenyl-porphyrin (Zn-TPPOH)) were adsorbed
on GaN, and Ni/Zn-TPPOH/GaN/Zn-TPPOH/Ni PD structures were fabricated.
This process was beneficial in two ways: first, the reverse-bias dark
current was reduced by 1000 times, and second, the photocurrent was
enhanced by ∼100 times, in comparison to the dark and photocurrent
values obtained for Ni/GaN/Ni MSM PDs, at high voltages of ±10
V. The responsivity of the devices was increased from 0.22 to 4.14
kA/W at 5 μW/cm2 optical power density at −10
V bias and at other voltages also. In addition to this, other PD parameters
such as photo-to-dark current ratio and UV-to-visible rejection ratio
were also enhanced. The spectral selectivity of the PDs was improved,
which means that the molecularly modified devices became more responsive
to UV spectral region and less responsive to visible spectral region,
in comparison to bare GaN-based devices. Photoluminescence measurements,
power-dependent photocurrent characteristics, and time-resolved photocurrent
measurements revealed that the MoL was passivating the defect-related
states on GaN. In addition, Kelvin probe force microscopy showed that
the MoL was also playing with the surface charge (due to surface states)
on GaN, leading to increased Schottky barrier height in dark conditions.
Resultant to both these phenomena, the reverse-bias dark current was
reduced for metal/MoL/GaN/MoL/metal PD structures. Further, the unusual
photoconductive gain in the molecularly modified devices has been
attributed to Schottky barrier lowering for UV-illuminated conditions,
leading to enhanced photocurrent.
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