Top-gate amorphous indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) are designed with numerical analysis to control their electron potential energy. Design simulations show the effects of structural design on the electrical characteristics of these TFTs. In particular, the thicknesses of the channel (tch) and conducting (tc) layers, which play vital roles in TFT electrical performance, are varied from 1 to 50 nm to investigate the effect of thicknesses on the electron potential energies of the channel region and the electrode-semiconductor interfaces. The potential energies are precisely optimized for efficient charge transport, injection, and extraction, thus enhancing the electrical performance of these devices. It is also demonstrated that tch mainly affects mobility and threshold voltage, while tc mainly affects on-current. An acceptable threshold voltage of 0.55 V and high mobility of 14.7 cm²V-1s-1 are obtained with a tch of 30 nm and tc of 10 nm. Controllability of the electron potential energies and electrical performance of IGZO TFTs by means of structural design will contribute to realization of next-generation displays that have large areas and high resolutions.

We investigate the possibility of shifting the absorption peak of the hybrid solar cell into the red to near infra-red (NIR) region using a ZnO optical spacer. Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b; 3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) exhibits a 700 nm wavelength peak absorption and is a low-bandgap polymer. Zinc oxide (ZnO) was used as an n-type semiconducting electron acceptor. The efficiency was enhanced by introducing a ZnO optical spacer layer. A finite-difference time-domain simulation was performed with the aim to extract the largest simulated short-circuit current density from the hybrid photovoltaic cell structure. Via the simulation, we also tuned the ZnO thickness to make the solar cell sensitive to the NIR wavelengths and thus obtained the optimal structures for various active layer thicknesses suitable for NIR absorption applications. This study aims to demonstrate the applicability of the PCPDTBT:ZnO hybrid solar cell as a multi-functional NIR absorber cum solar cell which has potential applications in energy harvesting window coating, NIR photodetector, and tandem solar subcell through the use of a ZnO optical layer to control the light-induced electric field distribution inside the device structure. (C )2019 Elsevier B.V. All rights reserved.

The lifetime of a device depends highly on that of its battery. In order to enhance the longevity of microsystems or sensor networks, it is necessary for these devices to be self-powered. Indoor photovoltaics allow the possibility of harvesting artificial light sources for powering microsystems. Whereas indoor photovoltaics based on single active layers have showed high efficiencies under LED lighting, tandem structures have yet to be tested extensively. In our study, we use finite-difference time-domain simulations to study the highest possible short-circuit current density that can be extracted from tandem organic devices. We compare the simulation results to the results for photovoltaic devices based on single bulk active layer heterojunctions. Our simulations found that although detailed balanced band gap calculations show tandem photovoltaics to be viable, the low-intensity emission spectra of white LED light sources can be better harvested by single active layer-based photovoltaics. The current-matching limitation of a tandem photovoltaic structure connected in series limits the highest output current and open-circuit voltage of the device and, thus, its performance for the illumination of lower intensity light.

In this paper,. an accurate analytical model has been developed to optimize the performance of an Interdigitated Graphene Electrode/p-silicon carbide (IGE/p-4H-SiC) Metal semiconductor Metal (MSM) photodetector operating in a wide range of temperatures. The proposed model considers different carrier loss mechanisms and can reproduce the experimental results well. An overall assessment of the electrodes geometrical parameters' influence on the device sensitivity and speed performances was executed. Our results confirm the excellent ability of the suggested Graphene electrode system to decrease the unwanted shadowing effect. A responsivity of 238 mu A/W was obtained under 325-nm illumination compared to the 16.7 mu A/W for the conventional Cr-Pd/p-SiC PD. A photocurrent to- dark-current ratio (PDCR) of 5.75 x 10(5) at 300K and 270 at 500K was distinguished. The response time was found to be around 14 mu s at 300K and 54.5 mu s at 500K. Furthermore, the developed model serves as a fitness function for the multi objective optimization (MOGA) approach. The optimized IGE/p-4H-SiC MSM-PD design not only exhibits higher performance in terms of PDCR (7.2 x 10(5)), responsivity (430A/cm(2)) and detectivity (1.3 x 10(14) Jones) but also balances the compromise between ultrasensitive and high-speed figures of merit with a response time of 4.7 mu s. Therefore, the proposed methodology permits to realize ultra-sensitive, high-speed SiC optoelectronic devices for extremely high temperature applications. (C) 2020 Elsevier B.V. All rights reserved.

Thin-film solar cells are predominately designed similar to a stacked structure. Optimizing the layer thicknesses in this stack structure is crucial to extract the best efficiency of the solar cell. The commonplace method used in optimization simulations, such as for optimizing the optical spacer layers’ thicknesses, is the parameter sweep. Our simulation study shows that the implementation of a meta-heuristic method like the genetic algorithm results in a significantly faster and accurate search method when compared to the brute-force parameter sweep method in both single and multi-layer optimization. While other sweep methods can also outperform the brute-force method, they do not consistently exhibit 100% accuracy in the optimized results like our genetic algorithm. We have used a well-studied P3HT-based structure to test our algorithm. Our best-case scenario was observed to use 60.84% fewer simulations than the brute-force method.

Few reports have researched on utilization of laser power conversion systems for wireless power transfer in aeronautical applications. III–V compound semiconductors are commonly used as photovoltaic (PV) power converters in the previous studies. We propose the prospects of using organic absorbers as PV power converters. For laser power conversion to be applied for portable devices, the PV module should be easily processable, thin, low-weight, and printable on flexible substrates. Organic PVs provide all the above advantages, and thus, could serve as a potential candidate for laser power harvesting applications. Moreover, they can also be made transparent, which could be utilized in power harvesting lamination coatings and windows. We had simulated the possibility of using single-junction and tandem photovoltaic structures for 670 nm and 850 nm laser power harvesting. FDTD simulations were conducted to optimize the PV structure in order to maximize the absorption at the laser wavelengths. A maximum PCE of 16.17% for single-junction PV and 24.85% for tandem PV was theoretically obtained.

We explore the effect of high-speed blade coating on electrical characteristics of conjugated polymer-based thin-film transistors (TFTs). As the blade-coating speed increased, the thickness of the polymer thin-film was naturally increased while the surface roughness was found to be unchanged. Polymer TFTs show two remarkable tendencies on the magnitude of field-effect mobility with increasing blade-coating speed. As the blade-coating speed increased up to 2 mm/s, the fieldeffect mobility increased to 4.72 cm²V-1s-1. However, when the coating speed reached 6 mm/s beyond 2 mm/s, the field-effect mobility rather decreased to 3.18 cm²V-1s-1. The threshold voltage was positively shifted from 2.09 to 8.29 V with respect to increase in blade-coating speed.

The printing of organic semiconductors (OSCs) by means of meniscus guided coating (MGC) has great potential for the fabrication of high-performance, uniform, and large area flexible electronics. Furthermore, surface energy patterning allows low-cost, large area manufacturing, and is a requirement for device isolation to achieve accurate drive and to minimize power consumption. We investigated the morphological and electrical characteristics of surface energy patterned OSCs coated using the MGC method. A unique phenomenon, contact line curvature-induced molecular misorientation effect, which occurs in the patterning of OSCs with the MGC method, is demonstrated. This effect is highly dependent on the pattern width which decided contact line curvature. It influences the charge transport properties and hence the field-effect mobility of organic thin-film transistors (OTFTs). OTFTs in widths ranging from 50 to 500 mu m were fabricated. The highest misorientation angle was induced in the 50 mu m pattern width and the corresponding OTFTs exhibited the highest mobility.

There are some reports related to applications of ultraviolet (UV) and water to enhance the electrical performance of metal oxide thin-film transistors (TFTs). We recently discovered that treatment timing and treatment method are also important for a good metal oxide thin-film formation. There are different influences on the metal oxide TFTs' electrical properties based on the UV irradiation and water treatment timing. The field-effect mobility of TFTs treated with UV-irradiation and water, which was spin-coated on the UV-irradiated film after pre-annealing, increased to 4.71 cm²V-1s-1 and 6.41 cm²V-1s-1. This was higher than the 3.39 cm²V-1s-1 field-effect mobility of non-treated TFTs. On the other hands, TFTs which were fabricated by the same method, with only varying the treatment time, after post-annealing, exhibited the tendency to show a decrease in field-effect mobility to 1.93 cm²V-1s-1 and 1.32 cm²V-1s-1, gradually, showing a contrasting tendency with the former conditions.

An in-depth study on the photovoltaic characteristics under indoor lights, i.e., light-emitting diode (LED), fluorescent lamps, and halogen lamps, was performed with varying the photoactive layer thickness (120-870 nm), by comparing those under 1-sun condition. The semi-crystalline mid-gap photoactive polymer, poly[(2,5-bis(2-hexyldecyloxy) phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl) benzo[c][1,2,5] thiadiazole)] (PPDT2FBT) and a fullerene derivative, [6,6]-phenyl C-71 butyric acid methyl ester (PC70BM) were used as a photoactive layer. In the contrary to the measurements under 1-sun condition, the indoor devices show a clearly different behavior, showing the thickness tolerant short-circuit current density (J(SC)) and fill factor (FF) values with 280-870 nm thick photoactive layers. The retained J(SC) and FF values of thick indoor devices were discussed in terms of the parasitic resistance effects based on the single-diode equivalent circuit model. The much lower series/shunt resistance (Rs/R-P) ratio was measured with thick photoactive layer (>= 280 nm), resulting in negligible decreases in the J(SC) and FF values even with a 870-nm-thick active layer under the LED condition. Under 1000 lx LED light, the PPDT2FBT:PC70BM device showed an optimum power conversion efficiency (PCE) of 16% (max power density, 44.8 mu W/cm(2)) with an open-circuit voltage of 587 mV, a J(SC) of 117 mu A/cm(2), and a FF of 65.2. The device with a 870-nm-thick active layer still exhibited an excellent performance with a PCE of 12.5%. These results clearly suggest that the critical parasitic resistance effects on the performance vary depending on the light illumination condition, and the large R-P associated with the viable thick photoactive layer and the well-matched absorption (of photoactive layer) with the irradiance spectrum (of indoor light) are essential to realize efficient indoor photovoltaic cells with high J(SC) and FF.

This work is inspired by Darwin's biological evolution theory: natural selection. We propose to use genetic evolutionary algorithm to optimize the search for the optimal thickness in solar cells with regards to maximizing short-circuit current density. Optical spacer layer thickness need to be optimized in order to achieve maximum absorption of the incoming light by the solar cell. In order to obtain the best optical spacer thickness, we perform multiple simulations with different number of population, number of generations, mutation probability, number of bits, and selection and crossover methods. Our preliminary experiments show that the introduction of evolutionary algorithm result in a satisfactorily accurate search method when compared to brute-force. The future works on utilizing the full ability of evolutionary algorithm will be presented at the conference.

A bulk heterojunction (BHJ) consisting of more than one donor/acceptor is one plausible way to improve the charge transport and/or the spectral absorption range in organic solar cells. Ternary and quaternary solar cells have shown promise in this regard. However, quaternary structures have not yet been intensively tested under indoor lighting conditions. A finite-difference time-domain (FDTD)-based simulation was used to solve for the electric field intensity distribution inside a quaternary photovoltaic device illuminated by 500 lx indoor white light emitting diodes (LEDs). We found that quaternary indoor photovoltaics (IPVs) showed peculiarly high oscillations in the simulated ideal short-circuit current density (Jsc,ideal). Here, we simulated the electric field intensity inside the photovoltaic, compared it to single BHJ photovoltaics, and deduced that the electric field intensity inside the active layer of the IPV was highly sensitive to its thickness due to interference between the incident light and the light reflecting from the back electrode. We also found that Poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) acted as the primary light absorber in the quaternary blend while poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) acted primarily as a cascade energy level and secondarily as a supplementary light absorber.

Recently, while increasing research has been focused toward improving the efficiency of various photovoltaic devices under low light intensities, few studies have reported on multi-donor-, multi-acceptor-based bulk heterojunctions (BHJ). In this study, we have demonstrated the utilization of a quaternary BHJ for indoor light energy harvesting applications. We utilized a PCDTBT:PTB7:PC61BM:PC71BM-based BHJ structure in order to improve the morphology, absorption window, and the charge transport properties of the photovoltaic device. The ability of ternary photovoltaics to attain high power-conversion efficiency (PCE) by improving the morphology and the charge transport properties had already been validated in another study. We show that the advantages of a stable quaternary solar cell can also be achieved with an optimized BHJ composition ratio of 5:5:3:12, which provides a PCE of 10.6%. Our device showed high shunt resistance and low series resistance, thus facilitating appreciable charge extraction even under low-intensity light conditions such as 500 lx white LED illumination.

Conventional solar cells are predominately designed similar to a stacked structure. Optimizing the layer thicknesses in this stack structure is crucial to extract the best efficiency of the solar cell. The commonplace method used in optimization simulations, such as for optimizing the optical spacer layers' thicknesses, is the parameter sweep. Our experiments show that the introduction of genetic algorithm based method results in a significantly faster and accurate search method when compared to brute-force parameter sweep method in both single and multi-layer optimization. While other sweep methods can also outperform the brute-force method, they do not consistently exhibit $100\%$ accuracy in the optimized results like our genetic algorithm. Our best case scenario was observed to utilize 57.9% less simulations than brute-force method.

Indoor lighting is a major source of energy consumption in buildings. However, reusability of the power output from the light source can help to recycle a small portion of the expended power. Third generation solar cells, such as organic solar cells (OSC), and dye-sensitized solar cells (DSSC), are semi-transparent and can be fabricated on flexible substrates. These desirable characteristics make them suitable candidates to be employed in applications such as smart windows, low-light harvesting systems, and wireless sensor nodes. Illuminance of household lighting is usually in the range of 500 lux. Our researched focused on optimizing the device structure of a conventional OSC to maximize its power conversion efficiency (PCE). When illuminated under a 500 lux light emitting diode (LED) light source. We have integrated optical modelling with empirical fitting of experimental data to conclude the most optimized structure for the low-light harvesting indoor photovoltaic (IPV) device.

Indoor solar cells are an attractive option to install in buildings to harvest the energy emitted by indoor lighting. They can be implemented as a stand-alone grid, or as part of an integrated energy harvesting unit. Previous research has utilized amorphous silicon and dye-sensitized solar cells for power generation from a fluorescent light source. In our study, we evaluated the applicability of a poly (3-hexylthiophene):indene-C60 bisadduct solar cell to harvest the light spectrum from an indoor light-emitting diode (LED). Because the absorption peak of poly (3-hexylthiophene) overlaps the LED spectrum peak, it serves as a good candidate for indoor light harvesting under an LED source. We have extracted the power conversion efficiency of the solar cell under different LED illuminance values, such as 200, 800, 1000, and 2000 lx. With the help of finite-difference time domain simulations, we optimized the solar device structure for each illuminance. The results detailed in this article were intended to assess the applicability of organic solar cells as indoor photovoltaics, and to provide a methodology to optimize the photovoltaic structure to maximize its efficiency.

The hysteresis of the solution-processed oxide thin-film transistors (TFTs) is fatal issue to interrupt stable operation. So, we came up with uni-directional pre-annealing to solve the problem. There are inevitable defects when solution-processed oxide TFTs are fabricated, due to the porosities by the solvent volatilization. Also oxygen vacancies needed for carrier generation in metal oxide semiconductor can be trap states inducing charge carrier trapping. Uni-directional pre-annealing improved the hysteresis, preventing randomly solvent evaporation and decreased the defects of the film. We can result in advanced stability of the solution-processed oxide TFTs, at the same time showing that the field effect mobility was enhanced from 3.35 cm2/Vs to 4.78 cm2/Vs simultaneously, and exhibiting better subthreshold swing from 0.89 V/dec to 0.23 V/dec.

The optical characteristics of nanoparticles will vary according to particle size. With decrease in the size of the nanoparticle (NP), the bandgap of the material increases, thus providing a blue-shift in the refractive index of the material. In this study, we analyzed the effect of different sized zinc oxide (ZnO) nanoparticle optical spacer on the ideal short-circuit current density (J(sc, ideal)) of an hybrid photovoltaic cell. ZnO was used as an optical spacer in the solar cell structure to improve the light absorbed in the active layer. Refractive index and extinction coefficient of different sized ZnO nanoparticles were calculated using tight binding model. We implemented these results in two different morphological models: nanoparticle model, and thin-film model. In the nanoparticle model, the ZnO NPs were considered as nanospheres which scatter the incoming light. Comparison of these models helped us to evaluate the improvement in the J(sc, ideal) due to scattering effects from nanoparticles. Finally, the optimized structure was obtained for different active layer thicknesses by varying the thickness of the ZnO layer.

Optical spacer interlayers are commonly used in solar cells to improve the power conversion efficiency (PCE) of the device. This paper reports a study on the effect of zinc oxide (ZnO) optical spacer interlayer on PCPDTBT:ZnO hybrid solar cell. Optical spacers help to concentrate the spatial distribution of electric field due to light onto the active layer, and thus, improve the light absorption in the active layer. Finite-Difference Time-Domain (FDTD) calculations was carried out on stacked solar cell structure using a simulation software, Lumerical FDTD solutions. Maxwell's equations were solved and the light absorbed by the active layer was computed. The design was optimized with regard to active layer thickness and ZnO optical spacer thickness.