Perovskite solar cells are still soaring in the science and technology world. For reaching efficient solar cells, the deposition method of perovskite highly matters. It severely affects the morphological structure and grain/crystal size of the deposited film which are very crucial factors. In this work, the solvent engineering, two-step solution deposition, and electrodeposition methods have been compared and studied morphologically. While substrate plays an important role in the quality of the deposited film, experiments have been carried out on both planar and mesopore $$\text {TiO}_2$$
 substrates. An image processing tool has been designed for quantitative surface analysis of the perovskite layers. The obtained results showed that the electrodeposition synthesis method on the mesopore substrate leads to an average of 99% surface coverage and the largest grain sizes (340.4 nm). It was demonstrated that the electrodeposited perovskite films had an average crystallite size of 39.11 nm which is slightly better than the other two methods. However, the solvent engineering method resulted in the most uniformity in grain sizes (standard deviation of 31.9 nm) for planar and (34.7 nm) for mesopore $$\text {TiO}_2$$
 substrates. According to the presented results, the electrodeposition seems to be the method of choice for perovskite deposition for solar applications.

Electrodeposition, solvent engineering, and two-step solution deposition of the perovskite films: morphological and structural study

We have investigated the characteristics of a hetero-dielectric ferroelectric tunnel (HD-FeTFET). Extensive simulations show that using a hetero-dielectric gate architecture in the lateral direction (non-ferroelectric/ferroelectric/non-ferroelectric) results in more desirable analog/RF characteristics. The proposed structure is compared with conventional tunnel field effect transistors (TFETs) and ferroelectric TFET (FeTFET). Simulation results manifest that HD-FeTFET is superior to other compared structures, and benefits from both ferroelectric and hetero-dielectric structure. Negative capacitance effect in ferroelectric causes a step-up voltage transformer, as a result the subthreshold swing decreases. Owing to two different dielectric constants in the hetero-dielectric structure, the electric field enhances; thereby, the on-state current increases. In this paper, important analog/RF figures of merit, such as cut-off frequency (fT), maximum oscillation frequency (fmax), transconductance frequency product, and intrinsic time delay (τ), are investigated. Also, linearity parameters including VIP2, VIP3, IIP3, and the 1-dB compression point are considered. We achieve average sub-threshold swing of 14 mV for 5 decades for HD-FeTFET, and is improved by ∼ 48% and ∼ 30% for TFET and FeTFET, respectively. Moreover, the ION/IOFF ratio and the on-state current for the proposed structure are 1011 and 5.3 × 10−7 (A/μm), respectively.

Impact of Hetero-Dielectric Ferroelectric Gate Stack on Analog/RF Performance of Tunnel FET

A novel-gated structure of aluminum (Al)—perovskite (CH3NH3PbI3)—indium tin oxide (ITO), with Al as source and ITO as drain terminals, has been reported. Ambipolar nature of CH3NH3PbI3 has been explored for the device channel. Two Schottky junctions are present at source–channel and channel–drain junctions with barriers of 0.4 and 0.6 eV, respectively. Both, n- and p-type FET-like characteristics have been observed, when the device was biased, accordingly. The triangular tunneling has been observed in the output and transfer characteristics. The device shows a higher current on-off ratio ( ${I}_{ \mathrm{\scriptscriptstyle ON}}/_{ \mathrm{\scriptscriptstyle OFF}})$ of 106 with a steeper and improved sub-threshold swing (SS) of 20 ± 2 mV/decade for P tunnel field-effect transistor (TFET). However, for N TFET, ${I}_{ \mathrm{\scriptscriptstyle ON}}/_{ \mathrm{\scriptscriptstyle OFF}}$ of 104 with SS of 30 ± 2 mV/decade has been obtained.

Metal-CH 3 NH 3 PbI 3 -Metal Tunnel FET

Frequency-dispersive impedance analysis of CH3NH3PbI3 perovskite is carried out under the external Direct current (DC) field to investigate the interplay of dielectric polarization and delocalized carrier transport. Switching of capacitance from positive to negative values is observed in the radio frequency range (42.1–42.5 MHz) for the external bias ranging from 0–4 V. The switching frequency outlined a decreasing trend with an increase in bias. Upon fitting the experimentally obtained dispersions, a bi-relaxation mechanism is unveiled. One of its constituents arises due to the typical Maxwell–Wagner interfacial polarization between the grain cores and boundaries and acts at the lower frequencies. The other one is manifested via hopping of delocalized carriers, resulting in a high frequency degenerative pseudo inductive response. The interference of these two mechanisms is manifested into an asymmetric Breit–Wigner–Fano profile of the dielectric susceptance spectra. The results are further elaborated from a theoretical point of view involving the energy band structure, electron localization function, and Mulliken charge distribution.

CH3NH3PbI3 as a radio frequency decoupling capacitor: interplay between Maxwell–Wagner polarization and a pseudo inductive response

A vertical resonant tunneling (RT) field effect transistor (VRTFET), fabricated using perovskite (CH3NH3PbI3), has been analyzed for sequential sharp negative differential resistance (NDR) peaks useful in multiple-valued logic devices. NDR peaks are attributed to the sub-bands formation within the parabolic shaped band gap, present at the channel and drain/source interface due to Schottky barriers. Ambipolar CH3NH3PbI3 imparts both p and n mode characteristics with RT NDR peaks. An unprecedentedly high (100 to 1000 V–1) curvature coefficient (ϒ) has been found with two NDR peaks at a short interval, whose positions shift left, with gate bias. Due to the ionic nature of CH3NH3PbI3, hysteresis has also been observed in the transfer characteristics. This structure can overcome the limit of 60 mV/decade as well as a curvature limit of 40 V–1, important parameters for analog and digital applications. So, these devices promise cheaper and easy fabrication at commercial scale operation at ultralow voltage and lo...

Perovskite Resonant Tunneling FET with Sequential Negative Differential Resistance Peaks

For the first time, we are proposing characteristic equation, which describes the behavior of an organic permeable base transistor (OPBT). For this, an OPBT has been fabricated and studied through the experimentally obtained ${I}_{C}$ / ${g}_{m}$ versus ${V}_{\mathsf {BE}}$ (base-emitter voltage) characteristics. The characteristic equation, i.e., collector current, ${I}_{C} = {k}$ ( ${V}_{\mathsf {BE}} - {V}_{\mathsf {th}})^{n}$ has been obtained through curve fitting and mathematical formulations. Six OPBTs (modified by inserting a layer of barrier material of either N, $\text{N}^{\prime }$ [(-di-[( $\alpha$ -naphthyl)-N, $\text{N}^{\prime }$ -diphenyl]-1, $1^{\prime }$ -biphenyl)-4, $4^{\prime }$ -diamine ( $\alpha$ -NPD) or N, $\text{N}^{\prime }$ -Bis(naphthalen-1-yl)-N, $\text{N}^{\prime }$ -bis(phenyl)-2,7-diamino-9, 9-(Spiro-NPB) between emitter and base layers) confirm that their transfer characteristics follow this equation with n varying between 1.1 and 2.2. The n has been found to be dependent on barrier material. The gain of the device is ${A}_{O} = \textit {nV}_{E}$ / ${V}_{\mathsf {BE}}$ , ${V}_{E}$ being the early voltage.

Modeling of Organic Permeable Base Transistor Based on Inverse of Transistor Efficiency ( ${I}_{C}$ / ${g}_{m}$ )

A simple vertical organic field-effect transistor (VOFET) structure has been fabricated using ambipolar 6, 13-bis (triisopropylsilyl ethynyl) pentacene (TIPSP) with a channel length (L) of 90 nm. This device can operate at –2 V which is much lower than the voltage, reported so far for the organic devices based on TIPSP. The first time, the authors are using transistor efficiency to extract VOFET's parameters. The threshold voltage (V th) of the device has been found to vary between 0.18 and 0.38 V with the current on/off ratio (I on /I off) of 104. The mobility (µ) of the device has been calculated as 0.62 cm2/Vs. The sub-threshold slope, transconductance (gm ), output conductance (g d), and early voltage (V E) have been found to be 140 ± 30 mV/decade, 2 µS, 10−6 S, and 1.3 ± 2 V, respectively.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-cds.2018.5173

Analysing the TIPSP‐based VOFET through transistor efficiency ( g m /I D )

A thin interfacial layer of 20 nm has been introduced to increase the barrier from 0.9 to 1.1 eV or 1.2 eV or 1.4 eV between the base and emitter of an organic permeable base transistor (OP...

The Effect of Base–Emitter Interfacial Layer on the Organic Permeable Base Transistor’s Characteristics

A vertical field effect transistor (VFET) with short channel length of 120 nm, fabricated using organic-inorganic perovskite (CH3NH3PbI3) material shows the ambipolar properties and switches from P mode to N mode or vice versa, just by changing the polarity of applied bias. The operating voltage is as low as 0.5 V, which allows it to be integrated with solar cell devices and hence having the possibility of battery less mobile gadgets. To ensure the quality of VFET with CH3NH3PbI3 as a channel length, different parameters have been extracted. The transistor efficiency (TE), mobility (μ p), and transconductance (gm) in P mode, have been estimated as 14 V−1, 1.5 cm2 V−1 s−1 and 500 ± 150 μS, respectively. For N mode, these parameters have been found to be as 4 V−1, 0.97 cm2V−1 s−1 and 60 ± 10 μS respectively. The hole and electron densities are found to be as ∼1016 cm−3 and ∼1014 cm−3 respectively which confirm the ambipolar nature of CH3NH3PbI3.

https://iopscience.iop.org/article/10.1088/2631-8695/aca746/pdf

Kalpana Agrawal

Papers

Metal-CH 3 NH 3 PbI 3 -Metal Tunnel FET

Modeling of Organic Permeable Base Transistor Based on Inverse of Transistor Efficiency ( ${I}_{C}$ / ${g}_{m}$ )

Analysing the TIPSP‐based VOFET through transistor efficiency ( g m /I D )

The Effect of Base–Emitter Interfacial Layer on the Organic Permeable Base Transistor’s Characteristics

Study of ambipolar properties of organic-inorganic CH3NH3PbI3 perovskite for vertical field effect transistor