On predicting annual output energy of 4-terminal perovskite/silicon tandem PV cells for building integrated photovoltaic application using machine learning.

Building integrated photovoltaic (BIPV), based on tandem PV cells, is considered a new alternative for combining solar energy with buildings. Accurately predicting the BIPV-harvested annual output energy (Eout,annual) is crucial for evaluating the BIPV performance. Machine learning (ML) is a potential candidate for solving such a problem without the time-consuming process of experimental investigations. This contribution proposes an artificial neural network (ANN) to predict the Eout,annual of 4-terminal perovskite/silicon (psk/Si) PV cells under realistic environmental conditions. The input variables of the proposed model consist of the input solar irradiance (Pin), incident light's angle (Ain), the PV module's temperature (Tmod), the psk absorber's thickness (Thpsk), and the psk absorber's bandgap (Bpsk). The input data were received from the simulated results. This work also evaluates the degree of importance of each input variable and optimizes the architecture of the ANN using the surrogate algorithm before predictions. The optimized ANN-3 (three hidden layers) model shows superior performance indicators, including a mean squared error of MSE = 0.02283, correlation coefficient R = 0.99999, and Willmott's index of agreement Iw = 0.99999. Consequently, the predicted highest Eout,annual at Bpsk of 1.71 eV is 297.73, 115.01, 193.98, and 97.6 kWh/m2 for the rooftop, east, south, and west facades, respectively.

Impact Analysis of Potential Induced Degradation on Crystalline Silicon Solar Cell Performance by Correlating Practical Diagnosis with MATLAB Simulation.

Extensive research on fault diagnosis is essential to detect various faults that occur to different photovoltaic (PV) panels to keep PV systems operating at peak performance. Here, we present an impact analysis of potential induced degradation (PID) on the current-voltage (I-V) characteristics of crystalline silicon (c-Si) solar cells. The impact of parasitic resistances on solar cell performance is highlighted and linked to fault and degradation. Furthermore, a Simulink model for a single solar cell is proposed and used to estimate the I-V characteristics of a PID-affected PV cell based on experimental results attributes. The measured data show that the fill factor (FF) drops by approximately 13.7% from its initial value due to a decrease in shunt resistance (Rsh). Similarly, the simulation results find that the fill factor degraded by approximately 12% from its initial value. The slight increase in measured data could be due to series resistance effects which were assumed to be zero in the simulated data. This study links simulation and experimental work to confirm the I-V curve behavior of PID-affected PV cells, which could help to improve fault diagnosis methods.

Optical and Electrical Transport Evaluations of n-Type Iron Pyrite Single Crystals.

Iron pyrite [cubic FeS2 (cFeS2)] is considered as an earth-abundant and low-cost thin-film photovoltaic material. However, the conversion efficiency of cFeS2-based solar cells remains below 3%. To elucidate this limitation, we evaluate the optical and electrical characteristics of cFeS2 single crystals that are grown using the flux method, thus providing us an understanding of the electron transport behavior of cFeS2 single crystals. The oxide layer on the surface of cFeS2, which can possibly have an influence on the electrical characteristics of cFeS2, is removed prior to characterization via optical spectroscopy and electrical transport measurement. The optical property of cFeS2 was found to have both indirect and direct transitions. We also observed the presence of a band tail below the conduction band. The obtained electrical transport behavior indicates that cFeS2 bulk exhibits a high defect density and a disordered phase, thus leading to the hopping conduction mechanism. Our results will pave the way for the development of photovoltaic applications with iron pyrite.

Impact of Mg level on lattice relaxation in a p-AlGaN hole source layer and attempting excimer laser annealing on p-AlGaN HSL of UVB emitters.

Mg-doped p-type semiconducting aluminium-gallium-nitride hole source layer (p-AlGaN HSL) materials are quite promising as a source of hole 'p' carriers for the ultraviolet-B (UVB) light-emitting diodes (LEDs) and laser diodes (LDs). However, the p-AlGaN HSL has a central issue of low hole injection due to poor activation of Mg atoms, and the presence of unwanted impurity contamination and the existence of a localized coherent state. Therefore, first the impact of the Mg level on the crystallinity, Al composition and relaxation conditions in the p-AlGaN HSL were studied. An increasing trend in the lattice-relaxation ratios with increasing Mg concentrations in the p-AlGaN HSL were observed. Ultimately, a 40%-60% relaxed and 1.4 µm thick p-AlGaN HSL structure with total threading dislocation densities (total-TDDs) of approximately ∼8-9 × 108 cm-2 was achieved, which almost matches our previous design of a 4 µm thick and 50% relaxed n-AlGaN electron source layer (ESL) with total-TDDs of approximately ∼7-8 × 108 cm-2. Subsequently, structurally a symmetric p-n junction for UVB emitters was accomplished. Finally, the influence of excimer laser annealing (ELA) on the activation of Mg concentration and on suppression of unwanted impurities as well as on the annihilation of the localized energy state in the p-AlGaN HSL were thoroughly investigated. ELA treatment suggested a reduced Ga-N bonding ratio and increased Ga-O, as well as Ga-Ga bonding ratios in the p-AlGaN HSL. After ELA treatment the localized coherent state was suppressed and, ultimately, the photoluminescence emission efficiency as well as conductivity were drastically improved in the p-AlGaN HSL. By using lightly polarized p-AlGaN HSL assisted by ELA treatment, quite low resistivity in p-type AlGaN HSL at room temperature (hole concentration is ∼2.6 × 1016 cm-3, the hole mobility is ∼9.6 cm2 V1 s-1 and the resistivity is ∼24.39 Ω. cm) were reported. ELA treatment has great potential for localized activation of p-AlGaN HSL as well as n- and p-electrodes on n-AlGaN and p-AlGaN contact layers during the flip-chip (FC) process in low operating UVB emitters, including UVB lasers.

Enhanced Thermoelectric Transport and Stability in Atomic Layer Deposited-HfO2/ZnO and TiO2/ZnO-Sandwiched Multilayer Thin Films.

Herein, enhancements in thermoelectric (TE) performance, both the power factor (PF) and thermal stability, are exhibited by sandwiching HfO2 and TiO2 layers onto atomic layer deposited-ZnO thin films. High-temperature TE measurements from 300 to 450 K revealed an almost two-fold improvement in electrical conductivity for TiO2/ZnO (TZO) samples, primarily owing to an increase in carrier concentration by Ti doping. On the other hand, HfO2/ZnO (HZO) achieved the highest PF values owing to maintaining Seebeck coefficients comparable to pure ZnO. HZO also exhibited excellent stability after multiple thermal cycles, which has not been previously observed for pure or doped ZnO thin films. Such improvement in both TE properties and thermal stability of HZO can be attributed to a shift in crystalline orientation from the a axis to c axis, as well as the high bond dissociation energy of Hf-O, stabilizing the ZnO structure. These unique properties exhibited by HZO and TZO thin films synthesized by atomic layer deposition pave the way for next-generation transparent TE devices.

Segregation-free bromine-doped perovskite solar cells for IoT applications.

Perovskite solar cells have attracted much attention as next-generation solar cells because of their high efficiency and low fabrication costs. Moreover, perovskite solar cells are a promising candidate for indoor energy harvesting. We investigated the effect of bandgap tuning on the characteristics of triple cation-based perovskite solar cells under fluorescent lamp illumination. According to the current density-voltage curves, perovskite solar cells with a wider bandgap than the conventional one exhibited improved open-circuit voltage without sacrificing short-circuit current density under fluorescent lamp illumination. Moreover, the wider bandgap perovskite films including a large amount of bromine in the composition did not show phase segregation, which can degrade the photovoltaic performance of perovskite solar cells, after fluorescent lamp illumination. Our results demonstrate the facile strategy to improve the performance of perovskite solar cells under ambient lighting and great potential of perovskite solar cells for indoor applications such as power sources for the internet of things.

Easy and green preparation of a graphene-TiO2 nanohybrid using a supramolecular biomaterial consisting of artificially bifunctionalized proteins and its application for a perovskite solar cell.

We report a novel preparation method for a graphene/TiO2 nanohybrid using a supramolecular biomaterial (CDT1). CDT1 can offer an increase in the dispersibility of graphene in water and subsequent complexation of graphene and TiO2. This nanohybrid was applied to a perovskite solar cell and success was achieved in improving its photoelectric conversion efficiency.

Instantaneous Semiconductor-to-Conductor Transformation of a Transparent Oxide Semiconductor a-InGaZnO at 45 °C.

The emphasis on ubiquitous technology means that future technological applications will depend heavily on transparent conducting materials. To facilitate truly ubiquitous applications, transparent conductors should be fabricated at low temperatures (<50 °C). Here, we demonstrate an instantaneous (<100 ns) and low-temperature (<45 °C at the substrate) method, excimer laser irradiation, for the transformation of an a-InGaZnO semiconductor into a transparent highly conductive oxide with performance rivaling traditional and emerging transparent conductors. Our analysis shows that the instantaneous and substantial conductivity enhancement is due to the generation of a large amount of oxygen vacancies in a-InGaZnO after irradiation. The method's combination of low temperature, extremely rapid process, and applicability to other materials will create a new class of transparent conductors for the high-throughput roll-to-roll fabrication of future flexible devices.

Effect of Gold Nanoparticle Distribution in TiO2 on the Optical and Electrical Characteristics of Dye-Sensitized Solar Cells.

Photoanodes comprising Au nanoparticles (GNPs) and thin TiO2 layers with a stacked structure were fabricated by repeating the application of TiO2 paste and GNP solutions on conductive glass to vary the distribution of GNPs in the TiO2 layer. The plasmon-enhanced characteristics of dye-sensitized solar cells (DSSCs) with such photoanodes were investigated. Both the absorption of the TiO2 layer and the performance of the DSSC are found to be most increased by plasmonic enhancement when GNPs are concentrated near the position in the TiO2 layer, which is the penetration depth of the incident light of wavelength corresponding to the maximum absorption of the N719 dye (~ 520 nm). When a GNP layer with a relatively high density of 1.3 µg/cm2 density was formed at its position, and two GNP layers with a relatively low density of 0.65 µg/cm2 were formed near the front side of the incident light, the short-circuit current density (Jsc) and energy conversion efficiency (η) of the DSSC were found to be 10.8 mA/cm2 and 5.0%, increases of 15 and 11%, respectively, compared with those of the DSSC without GNPs. Our work suggests that optimization of the distribution of GNPs in the TiO2 layer is very important for improving the performance of DSSCs fabricated by utilizing GNPs.

Fabrication of Nanoshell-Based 3D Periodic Structures by Templating Process using Solution-derived ZnO.

Fabrication methods for a 3D periodic nanostructure with excellent and unique properties for various applications, such as photonic and phononic crystals, have attracted considerable interest. Templating processes using colloidal crystals have been proposed to create nanoshell-based 3D structures over a large area with ease. However, there are technical limitations in structural design, resulting in difficulties for structural flexibility. Here, we demonstrate a combination of proximity field nanopatterning and infiltration processes using solution-derived ZnO for a nanoshell-based 3D periodic structure with high structural flexibility and controllability. A unique process of infiltration of a solution-derived material into a polymeric template prepared by a proximity field nanopatterning process achieves the fabrication of a pre-formed layer that works as a protective layer for the template and framework for the inverse structure. Subsequently, this process shows the controllability of nanoshell thickness and significant improvement in the structure height shrinkage factor (16%) compared to those of a previous non-vacuum infiltration method (34%). The proposed method offers high controllability and flexibility in the design of structural sizes, leading to further development toward nanoshell-based 3D structures for various applications including energy devices and sensors.

Biotemplated Synthesis of TiO2-Coated Gold Nanowire for Perovskite Solar Cells.

Fibrous nanomaterials have been widely employed toward the improvement of photovoltaic devices. Their light-trapping capabilities, owing to their unique structure, provide a direct pathway for carrier transport. This paper reports the improvement of perovskite solar cell (PSC) performance by a well-dispersed TiO2-coated gold nanowire (GNW) in a TiO2 cell layer. We used an artificially designed cage-shaped protein to synthesize a TiO2-coated GNW in aqueous solution under atmospheric pressure. The artificially cage-shaped protein with gold-binding peptides and titanium-compound-biomineralizing peptides can bind GNWs and selectively deposit a thin TiO2 layer on the gold surface. The TiO2-coated GNW incorporated in the photoelectrodes of PSCs increased the external quantum efficiency within the range of 350-750 nm and decreased the internal resistance by 12%. The efficient collection of photogenerated electrons by the nanowires boosted the power conversion efficiency by 33% compared to a typical mesoporous-TiO2-nanoparticle-only electrode.

Interface Optoelectronics Engineering for Mechanically Stacked Tandem Solar Cells Based on Perovskite and Silicon.

Engineering of photonics for antireflection and electronics for extraction of the hole using 2.5 nm of a thin Au layer have been performed for two- and four-terminal tandem solar cells using CH3NH3PbI3 perovskite (top cell) and p-type single crystal silicon (c-Si) (bottom cell) by mechanically stacking. Highly transparent connection multilayers of evaporated-Au and sputtered-ITO films were fabricated at the interface to be a point-contact tunneling junction between the rough perovskite and flat silicon solar cells. The mechanically stacked tandem solar cell with an optimized tunneling junction structure was ⟨perovskite for the top cell/Au (2.5 nm)/ITO (154 nm) stacked-on ITO (108 nm)/c-Si for the bottom cell⟩. It was confirmed the best efficiency of 13.7% and 14.4% as two- and four-terminal devices, respectively.

Selection of a novel peptide aptamer with high affinity for TiO2-nanoparticle through a direct electroporation with TiO2-binding phage complexes.

We have developed an easy and rapid screening method of peptide aptamers with high affinity for a target material TiO2 using M13 phage-display and panning procedure. In a selection step, the phage-substrate complexes and Escherichia coli cells were directly applied by electric pulse for electroporation, without separating the objective phages from the TiO2 nanoparticles. Using this simple and rapid method, we obtained a novel peptide aptamer (named ST-1 with the sequence AYPQKFNNNFMS) with highly strong binding activity for TiO2. A cage-shaped protein fused with both ST-1 and an available carbon nanotube-affinity peptide was designed and produced in E. coli. The multi-functional supraprotein could efficiently mineralize a titanium-compound around the surface of single-wall carbon nanotubes (SWNTs), indicating that the ST-1 is valuable in the fabrication of nano-composite materials with titanium-compounds. The structural analysis of ST-1 variants indicated the importance of the N-terminal region (as a motif of AXPQKX6S) of the aptamer in the TiO2-binding activity.

Creating Reversible p-n Junction on Graphene through Ferritin Adsorption.

An alternative way to construct a stable p-n junction on graphene-based field effect transistor (G-FET) through physical adsorption of ferritin (spherical protein shell) is presented. The produced p-n junction on G-FET could also operate through water-gate. Native ferritins are known to be negatively charged in wet condition; however, we found that native negatively charged ferritins became positively charged after performing electron beam (EB)-irradiation. We utilized this property to construct p-n junction on G-FET. We found also that EB-irradiation could remove the effect of charged impurity adsorbed on graphene layer, thus the Dirac point was adjusted to gate voltage Vg = 0.

High-density carrier-accumulated and electrically stable oxide thin-film transistors from ion-gel gate dielectric.

The use of indium-gallium-zinc oxide (IGZO) has paved the way for high-resolution uniform displays or integrated circuits with transparent and flexible devices. However, achieving highly reliable devices that use IGZO for low-temperature processes remains a technological challenge. We propose the use of IGZO thin-film transistors (TFTs) with an ionic-liquid gate dielectric in order to achieve high-density carrier-accumulated IGZO TFTs with high reliability, and we discuss a distinctive mechanism for the degradation of this organic-inorganic hybrid device under long-term electrical stress. Our results demonstrated that an ionic liquid or gel gate dielectric provides highly reliable and low-voltage operation with IGZO TFTs. Furthermore, high-density carrier accumulation helps improve the TFT characteristics and reliability, and it is highly relevant to the electronic phase control of oxide materials and the degradation mechanism for organic-inorganic hybrid devices.

Thermo-stable carbon nanotube-TiO2 nanocompsite as electron highways in dye-sensitized solar cell produced by bio-nano-process.

We produced a thermostable TiO2-(anatase)-coated multi-walled-carbon-nanotube (MWNT) nanocomposite for use in dye-sensitized solar cells (DSSCs) using biological supuramolecules as catalysts. We synthesized two different sizes of iron oxide nanoparticles (NPs) and arrayed the NPs on a silicon substrate utilizing two kinds of genetically modified cage-shaped proteins with silicon-binding peptide aptamers on their outer surfaces. Chemical vapor deposition (CVD) with the vapor-liquid-solid phase (VLS) method was applied to the substrate, and thermostable MWNTs with a diameter of 6 ± 1 nm were produced. Using a genetically modified cage-shaped protein with carbon-nanomaterials binding and Ti-mineralizing peptides as a catalyst, we were able to mineralize a titanium compound around the surface of the MWNT. The products were sintered, and thin TiO2-layer-coated MWNTs nanocomoposites were successfully produced. Addition of a 0.2 wt% TiO2-coated MWNT nanocomposite to a DSSC photoelectrode improved current density by 11% and decreased electric resistance by 20% compared to MWNT-free reference DSSCs. These results indicate that a nanoscale TiO2-layer-coated thermostable MWNT structure produced by our mutant proteins works as a superior electron transfer highway within TiO2 photoelectrodes.

Floating gate memory with charge storage dots array formed by Dps protein modified with site-specific binding peptides.

We report a nanodot (ND) floating gate memory (NFGM) with a high-density ND array formed by a biological nano process. We utilized two kinds of cage-shaped proteins displaying SiO2 binding peptide (minTBP-1) on their outer surfaces: ferritin and Dps, which accommodate cobalt oxide NDs in their cavities. The diameters of the cobalt NDs were regulated by the cavity sizes of the proteins. Because minTBP-1 is strongly adsorbed on the SiO2 surface, high-density cobalt oxide ND arrays were obtained by a simple spin coating process. The densities of cobalt oxide ND arrays based on ferritin and Dps were 6.8 × 10(11) dots cm(-2) and 1.2 × 10(12) dots cm(-2), respectively. After selective protein elimination and embedding in a metal-oxide-semiconductor (MOS) capacitor, the charge capacities of both ND arrays were evaluated by measuring their C-V characteristics. The MOS capacitor embedded with the Dps ND array showed a wider memory window than the device embedded with the ferritin ND array. Finally, we fabricated an NFGM with a high-density ND array based on Dps, and confirmed its competent writing/erasing characteristics and long retention time.

Silica-sol-based spin-coating barrier layer against phosphorous diffusion for crystalline silicon solar cells.

The phosphorus barrier layers at the doping procedure of silicon wafers were fabricated using a spin-coating method with a mixture of silica-sol and tetramethylammonium hydroxide, which can be formed at the rear surface prior to the front phosphorus spin-on-demand (SOD) diffusion and directly annealed simultaneously with the front phosphorus layer. The optimization of coating thickness was obtained by changing the applied spin-coating speed; from 2,000 to 8,000 rpm. The CZ-Si p-type silicon solar cells were fabricated with/without using the rear silica-sol layer after taking the sheet resistance measurements, SIMS analysis, and SEM measurements of the silica-sol material evaluations into consideration. For the fabrication of solar cells, a spin-coating phosphorus source was used to form the n(+) emitter and was then diffused at 930°C for 35 min. The out-gas diffusion of phosphorus could be completely prevented by spin-coated silica-sol film placed on the rear side of the wafers coated prior to the diffusion process. A roughly 2% improvement in the conversion efficiency was observed when silica-sol was utilized during the phosphorus diffusion step. These results can suggest that the silica-sol material can be an attractive candidate for low-cost and easily applicable spin-coating barrier for any masking purpose involving phosphorus diffusion.

Biological construction of single-walled carbon nanotube electron transfer pathways in dye-sensitized solar cells.

We designed and mass-produced a versatile protein supramolecule that can be used to manufacture a highly efficient dye-sensitized solar cell (DSSC). Twelve single-walled carbon-nanotube (SWNT)-binding and titanium-mineralizing peptides were genetically integrated on a cage-shaped dodecamer protein (CDT1). A process involving simple mixing of highly conductive SWNTs with CDT1 followed by TiO2 biomineralization produces a high surface-area/weight TiO2 -(anatase)-coated intact SWNT nanocomposite under environmentally friendly conditions. A DSSC with a TiO2 photoelectrode containing 0.2 wt % of the SWNT-TiO2 nanocomposite shows a current density improvement by 80% and a doubling of the photoelectric conversion efficiency. The SWNT-TiO2 nanocomposite transfers photon-generated electrons from dye molecules adsorbed on the TiO2 to the anode electrode swiftly.