Na0.5Bi0.5TiO3-based ceramics have been paid great attention as Pb-free piezoelectric and electrical energy storage materials. Here, adding 10 mol% BiFeO3 in Na0.5Bi0.5TiO3–SrTiO3 binary system, 0.5Na0.5Bi0.5TiO3–0.4SrTiO3–0.1BiFeO3 ceramics were prepared by a conventional solid-state reaction method. Dielectric measurements reflected a near-plateau dielectric response at high temperature, e.g., the mid-dielectric permittivity of 2052 with the variation within ±10% from 57 to 371 °C and within ±15% from 54 to 371 °C for the ceramic sintered at 1100 °C. At a moderate electric field of 70 kV/cm, a capacitor made by the ceramic has an electrical energy storage density of 0.95 J/cm3, while the polarization has yet saturated at the moderate electric field. These results suggest that 0.5Na0.5Bi0.5TiO3–0.4SrTiO3–0.1BiFeO3 ceramic is a promising novel material with thermally stable dielectric permittivity and high electrical energy storage property for applications in high-temperature electronics.

The validity of Mn element on enhanced energy storage performance and fatigue resistance of Mn-doped 0.7Na0.5Bi0.5TiO3–0.3Sr0.7Bi0.2TiO3 lead-free ferroelectric ceramics (BNT–BST–xMn) is certified by doping. The effects of Mn modification on the dielectric behavior, ferroelectric, energy storage properties, and AC impedance are comprehensively investigated. It is found that the average grain size of the ceramics modified by Mn additions is reduced slightly. Moreover, the relaxor properties are evidently enhanced with the increased Mn content. The AC impedance spectra can even better clarify the dielectric response and relaxor behavior. The results suggest that both of the dielectric response and relaxor behavior are determined by defects especially concentration of the oxygen vacancy. The superior energy storage properties are realized at x = 0.05 with an energy storage density (Wrec) of 1.33 J/cm3 as well as energy storage efficiency (η) of 86.2% at 100 kV/cm, accompanied with a superior thermal stability. BNT–BST–5Mn ceramics can maintain a stable energy storage performance within 106 fatigue cycles, indicating an excellent fatigue resistance.

Potassium and cerium co-doped Bi4Ti2.86W0.14O12 ceramics with a formula of (K0.5Ce0.5)xBi4−xTi2.86W0.14O12 (abbreviated as KC100x-BITW, x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) were prepared by a conventional solid-state reaction method. The effect of (K0.5Ce0.5) complex doping amount on the structure, dielectric, and piezoelectric properties of the KC100x-BITW ceramics was investigated. X-ray diffraction results indicated that the KC100x-BITW ceramics are Aurivillius-type phase with the bismuth layer structure. (K0.5Ce0.5) complex addition first increases and then decreases the grain size which can be observed by scanning electron microscopy. With the increase of (K0.5Ce0.5) complex doping amount, the Curie temperature (TC) was slightly decreased from 632 to 608 oC. The dielectric and piezoelectric properties were optimized in KC100x-BITW ceramics with x = 0.08 as follows: d33 = 24 pC/N, kp = 8.2%, Qm = 6766, εr = 135 (@100 kHz), tanδ = 0.28% (@100 kHz), Tc = 611 oC, and resistivity ρ = 2.9 × 106 Ω cm at 500 oC, indicating that the KC100x-BITW ceramics are suitable for high-temperature piezoelectric sensing applications.

A new series of ternary perovskite 0.975(0.8Bi1/2Na1/2TiO3–0.2Bi1/2K1/2TiO3)–0.025Bix/3Mgy/3Nbz/3O3 (BNT–BKT–BMN, BMN-xyz) ceramics were designed and synthesized. The effect of the element ratio in the doping component BMN on the strain, ferroelectric, piezoelectric, and dielectric properties of the BNT–BKT matrix were studied. The BMN-430 composition without Nb element exhibits the typical features of non-ergodic relaxor, which is characterized by a higher piezoelectric coefficient d33 and a butterfly-shaped strain curve with negative strain. The introduction of trace Nb can significantly enhance the ergodicity of the system, reflecting in the high positive strain response and strain coefficient $\lpar {d_{33}^\ast \gt 750\;{\rm pm/V}} \rpar$ of BMN-321 composition. In contrast, there is no significant difference in the properties between the presence and absence of Mg element. The temperature-dependent electrical behaviors of BMN-xyz ceramics were analyzed based on impedance spectroscopy. This study may be helpful to the design of the chemical modification strategy for the BNT-based relaxor ferroelectrics.

Lead-free perovskite layers may provide a good alternative to the commonly used lead-halide-based perovskite absorber layers in photovoltaics. Energy level alignment of the active semiconductor with contact layers is a key factor in device performance. Kelvin probe force microscopy was used during vapor deposition of C60 onto formamidinium tin iodide to investigate contact formation with detailed local resolution of these materials that are significant for photovoltaic cells. Significant differences dependent on the growth rate of C60 were detected. Sufficiently high deposition rates were essential to reach compact C60 films needed for good contact. A space charge layer larger than 90 nm within the C60 layer was established without indication of interfacial dipoles. The present analysis gives a clear indication of a well-functioning contact of fullerenes to formamidinium tin iodide that is suitable for the use in photovoltaic devices provided that thin compact fullerene films are formed.

In the last years, perovskite solar cells have attracted great interest in photovoltaic (PV) research due to their possibility to become a highly efficient and low-cost alternative to silicon solar cells. Cells based on the widely used Pb-containing perovskites have reached power conversion efficiencies (PCE) of more than 20 %. One of the major hurdles for the rapid commercialization of perovskite photovoltaics is the lack of deposition tools and processes for large areas. Chemical vapor deposition (CVD) is an appealing technique because it is scalable and furthermore features superior process control and reproducibility in depositing high-purity films. In this work, we present a novel showerhead-based CVD tool to fabricate perovskite films by simultaneous delivery of precursors from the gas phase. We highlight the control of the perovskite film composition and properties by adjusting the individual precursor deposition rates. Providing the optimal supply of precursors results in stoichiometric perovskite films without any detectable residues.

The energy level alignment that occurs at the interfaces in planar-hetero structured perovskite photovoltaic devices strongly influences the charge transport across the interface, and thus plays a crucial role in overall device performance. To directly observe the energy level alignment requires pristine homogeneous surfaces that are free of contamination including adventitious carbon. Co-evaporation offers the ability to grow perovskite thin films in-situ, and the method involves thermally evaporating the perovskite precursors such as PbI2 and CH3NH3I. Early reports have shown that the perovskite film formation and stoichiometry are problematic at ultralow coverages. In particular, it was reported that there was excessive PbI2 and a deficiency in CH3NH3I. Using photoemission spectroscopy, we investigated the perovskite precursor PbI2 on gold and highly oriented pyrolytic graphite (HOPG) surfaces. Results show that the nature of the surface and the deposition conditions can strongly influence the film formation. Excessive iodine observed in the initial evaporation stages appears to be substrate dependent, and this may influence the overall energy level alignment.

The majority of highly efficient perovskite light-emitting diodes (PeLED) contain PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrenesulfonate) as hole transport layer (HTL). However, the hygroscopic and acidic nature of PEDOT:PSS may lead to deterioration of PeLED performance. Moreover, due to its inferior electron-blocking properties, an additional electron-blocking layer (EBL) is required to establish charge balance and consequently obtain superior emission characteristics in typically electron-rich PeLED structures. In this work, PTAA (poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)) serving both as HTL and EBL is employed to substitute PEDOT:PSS in PeLED. The perovskite CsPbBr3 is chosen as emissive layer (EML) material due to its high color purity and photoluminescence (PL) quantum yield. Dense CsPbBr3 films are fabricated on PTAA-coated ITO substrates by employing a one-step spin-coating approach based on nonstoichiometric perovskite precursor solutions. To suppress non-radiative recombination, a small amount of methylammonium bromide (MABr) is incorporated in the CsPbBr3 lattice. The resulting films exhibit excellent coverage and PL intensity. PeLED containing pure CsPbBr3 films as EML show a green emission with a peak at 520 nm, maximum luminance of 11,000 cd/m2, an external quantum efficiency (EQE) of 3.3 % and a current efficiency (CE) of 10.3 cd/A. Further enhancement to 21,000 cd/m2, 7.5 % and 27.0 cd/A is demonstrated by PeLED with MABr-doped CsPbBr3 layers.

X-ray imaging is a valuable technique used for medical imaging and non-destructive inspection of industrial products. However, the radiation may put humans at risk of developing cancer. Consequently, highly sensitive X-ray detectors, which enable X-ray imaging at a low dose rate, are required. Metal halide perovskite materials have demonstrated excellent X-ray detection performance including a high sensitivity owing to their high absorption coefficient, high carrier mobility, and long carrier lifetime. However, perovskite thick films with a large area, which is essential to realize the application of such materials to X-ray imaging devices have not been extensively investigated. To this end, in this study, a polymer is employed as a buffer layer to avoid film exfoliation, which makes it difficult to fabricate perovskite thick films, and a 110-μm-thick CsPbBr3 film is successfully obtained using a scalable solution method. In addition, an X-ray detector based on the CsPbBr3 thick film is fabricated, which demonstrates a sensitivity of 11,840 μC Gyair–1 cm–2. This sensitivity is approximately 600 times higher than that of the existing commercial a-Se X-ray detectors.

In this work, lead halide perovskite photodetectors were fabricated by a laser-assisted rapid fabrication method. A microchannel was engraved on an indium tin oxide (ITO) coated polyethylene terephthalate (PET) conductive flexible substrate using a CO2 laser source. The channels were filled by methylammonium lead halide perovskite (CH3NH3PbI3) using the capillary motion of perovskite first-step method precursor. CYTOP and the low-cost commercially available FluroPel were used as a top protective coating layer to suppress the decomposition of the perovskite channel. X-ray diffraction pattern (XRD) was used to measure the stability of the perovskite. Strong humidity resistant and self-healing behavior were observed in both devices. The performance of the photodetectors was compared by measuring electrical and optical characteristics over time. This study will help in the low-cost fabrication of perovskite-based devices.

Development of high-efficiency solar cell modules and new application fields are significant for the further development of photovoltaics (PV) and creation of new clean energy infrastructure based on PV. Especially, development of PV-powered EV applications is desirable and very important for this end. This paper shows analytical results for efficiency potential of various solar cells for choosing candidates of high-efficiency solar cell modules for automobile applications. As a result of analysis, Si tandem solar cells are thought to be some of their candidates. This paper also overviews efficiency potential and recent activities of various Si tandem solar cells such as III-V/Si, II-VI/Si, chalcopyrite/Si, perovskite/Si and nanowire/Si tandem solar cells. The III-V/Si tandem solar cells are expected to have a high potential for various applications because of high efficiency with efficiencies of more than 36% for 2-junction and 42 % for 3-junction tandem solar cells under 1-sun AM1.5 G, lightweight and low-cost potential. Recent results for our 28.2 % efficiency and Sharp’s 33% mechanically stacked InGaP/GaAs/Si 3-junction solar cell are also presented. Approaches to automobile application by using III-V/Si tandem solar cells and static low concentration are presented.

This research automates edge detection for perovskite crystal grains using machine learning (ML). Once the edges of the crystal grains are located, a flood-fill algorithm can be used to find the distribution of crystal grain areas. The ML algorithm uses GNU Octave to run a regularized logistic regression algorithm that classifies each pixel of an input image as part of an edge or not part of an edge. The basic features used for the algorithm are each pixel’s grayscale intensity, its Sobel derivative. Higher order Sobel derivatives, higher degree polynomial terms, and intensities convolved by various kernels were used as additional features to improve the program’s accuracy and true-positive rate. Training data is obtained by using non-ML Canny Edge Detection to annotate the edges an SEM image of a pure perovskite solar cell (PSC). The classifier exhibits an 85.58% accuracy and produces an edge mask that clearly outlines the crystals visually. The ML edge mask exhibits far fewer false-positive mis-classifications for pixels in the middle of the crystals than Canny. However, the ML mask’s edges are fainter, owing to a lower true-positive classification rate. Using more kernels, higher order derivatives, and higher degree polynomial terms all significantly increased the true positive rate of the classifier, leading to thicker edges. This algorithm can greatly accelerate perovskite solar cell research (and potentially any research requiring particle size analysis), automating a process scientists previously had to perform by hand. This will facilitate the search for a solution for the world’s growing demands for renewable energy.

Using first-principles calculation, we investigate water-dissociation dynamics in a Σ5 tilt grain boundary (GB) of Methyl-Ammonium Lead Triiodide (MAPbI3) perovskite. We find that the water dissociation process undergoes with two-step reaction at the GB: one of H ions of a water molecule that segregates into the GB is dissociated, migrates along the GB, and is attracted by an N atom in the MAPbI3, following the H-ion release from the ammonium. The process thereby generates OH− ion and, in turn, leads to possible initiation of the degradation for crystallinity in the perovskite.

Cesium lead iodide perovskite (CsPbI3) with excellent optical and electrical properties have attracted numerous academic attentions. Specifically, the black cubic phase CsPbI3 with a direct band gap of 1.74 eV has been most appropriate materials for various optoelectronic applications, especially for photovoltaic (PV), Light-Emitting Diodes (LED) and photodetector applications1. However, the preferred cubic phase of bulk CsPbI3 (α-CsPbI3) is usually only stable at high temperatures and it will undergo an immediate phase transformation to orthorhombic phase (δ-CsPbI3) after fabrication at room temperature. In this work, we have discovered a convenient CVD method to investigate the growth behavior of the cubic α-CsPbI3 film on the porous alumina substrate. The lead iodide and cesium iodide were used as the precursors for the deposition of CsPbI3. The porous alumina with high surface area and large pore volume was used as growth substrate. It was shown that the porous alumina promoted the growth of CsPbI3 film by absorbing the precursor and increasing the nucleation density. The prepared CsPbI3 film emitted strong and stable red light under ultraviolet light excitation at room temperature and ambient atmosphere. The lead iodide was absorbed on the surface of the porous alumina firstly then reacted with cesiumiodide to form the CsPbI3. The successful preparation of the CsPbI3 by the direct CVD method paves the way for its large scale growth and application in optoelectronic devices.

Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light emitting devices due to optoelectronic properties. Understanding the surface chemistry of these materials is of importance as surface defects can introduce trap-states which reduce their functionality. Here we use Density Functional Theory (DFT) to model surface defects introduced by Pb2+ on a CsPbBr3 NC atomistic model. Two types of defects are studied: (i) an under-coordinated Pb2+ surface atom and (ii) Pb2+ atomic or molecular adsorbents to the NC surface. From the DFT calculations we compute the density of states (DOS) and absorption spectra of the defect models to the pristine fully-passivated NC model. We observe that for the low surface defect regime explored here that neither (i) or (ii) produce trap-states inside of the bandgap and exhibit bright optical absorption for the lowest energy transition. From the models studied, it was found that the Pb2+ atomic absorbent provides broadening of the conduction band edge, which implies chemisorption of Pb2+ to the NC surface. At higher defect densities it would be expected that Pb2+ atomic absorbents would introduce trap-states and degrade the opto-electronic properties of these materials.

Bismuth ferrite (BiFeO3) and La-, Nd- and Gd-substituted bismuth ferrite of the Bi1-xLaxFeO3, Bi1-xNdxFeO3, and Bi1-xGdxFeO3 types with the atomic part of the substitution element x equal up to 0.20 were synthesized by the solid-state reaction method using powders of oxides Bi2O3, Fe2O3, and La2O3, or Nd2O3, or Gd2O3 of pure grade quality and investigated using X-ray diffraction analysis. The magnetization was measured in the magnetic field up to 6.5⋅106 A/m at 5 and 300 K. It was found that the total substitution up to 0.20 atomic part of Bi by La, Nd, and Gd leads to the paramagnetic behavior of the doped bismuth ferrite at low temperatures in a wide range of magnetic field. Strong nonlinear dependence of magnetization on the magnetic field was detected and a ferromagnetic-like dependence of magnetization was observed for small magnetic fields. This can be explained by the exchange interaction between doping magnetic ions, as well as by the exchange interaction of these ions with ions of iron. The enhancement of magnetic properties with the increase of the content of the substitution is monotone and is more pronounced for the Bi1-xGdxFeO3 ceramics.

The effects of La-substitution into SrTiO3 (STO) perovskite oxides on their phase structure, formation enthalpy and electrical conductivity have been investigated. La substitution in STO has been reported to show a significant enhancement in electronic conductivity in a wide-band-gap layered perovskite compound STO. Mixture of Lanthanum and Titanium oxide may lead to various phases including La2/3TiO3, La2Ti2O7 and La2TiO5. In this work, more than 50 structural models have been constructed by considering ionic state substituents, distance between substituents and their concentrations. We investigated the formation enthalpy, elastic properties and band gap by density functional theory (DFT) calculations. We have also investigated the effect of reducing environment on La2/3TiO3. The computed bulk modulus (∼2.4 % deviation) and band gap (∼12% deviation) of STO are in good agreement with the literature. Our results indicate that La substitution into STO could significantly reduce the band gap. Reduction in band gap is maximum when the substituents is present at low concentrations. Internal position of La substituents in STO affects the band gap marginally while energy remains almost same. Formation enthalpy of La2/3TiO3 from LaTiO3 is around 2 eV. La2/3TiO3 acts as band insulator (band gap = 2.8 eV). In reducing environment, the band gap of La2/3TiO3 significantly reduces. Sr substitution in La2/3TiO3 lower the band gap and formation enthalpy. La2Ti2O7 and La2TiO5 have higher band gap and lower bulk modulus than STO. Sr substitution is not feasible in La2Ti2O7 and La2TiO5.

Reported conversion efficiencies of lead based perovskite solar cells keep increasing steadily. But next to the demand for high efficiency, the need for analogue non-toxic material systems remains. One promising lead free absorber material is the double perovskite Cs2AgBiBr6. Interest in this and other double perovskites has been increasing in the last three years and several solar cells using different device structures have been reported. However, the efficiency of these solar cells is merely in the range of 2%. To further improve solar cell performance we prepared mixed bismuth-antimony double perovskite Cs2AgBi1-xSbxBr6 where different fractions of antimony (x=0.125, 0.25, 0.375, 0.50) are used. This was motivated by reports of lower bandgap values in these mixed system. After the optimization of preparation of these thin films, we have carefully analysed the effects on the structure, composition, electronic structure, as well as optical properties. Finally, we have fabricated Bi-Sb mixed double perovskite solar cells in a mesoscopic device architecture.

Roll-to-roll slot-die coating with a meniscus guide is used to deposit several layers in a P-I-N perovskite solar cell stack, including the perovskite layer. The use of various length meniscus guides as part of the slot-die head allows controlled coating of these layers at a common coating speed. The length of meniscus guide used is optimised and related to the rheology of the coated ink and appropriate choice of meniscus guide length provides a way to avoid flooding of the coated area and improve coating definition. Initial coating trial results suggest the low-flow limit of slot-die coating is still applicable when using a meniscus guide, which is an important and previously unreported observation, application of this theory to meniscus guide coating provides a useful tool for rapidly determining the appropriate coating conditions that can be used as part of a manufacturing process. This is further explored through the deposition of perovskite solar cells by roll-to-roll slot-die coating. The perovskite layer is deposited using a sequential slot-die deposition process using a low toxicity dimethyl sulfoxide ink for the lead iodide layer, it is found that increasing the drying oven temperature and air flow rate can be used to improve the uniformity of the layer but this can also result in deformation of the plastic substrate. Functioning perovskite solar cells are demonstrated using this technique, but a large variation is found between device performances which is attributed to the poor uniformity of the perovskite layer and damage caused to the substrate by excessive heating.

Thermoelectric materials can play an important role to develop a sustainable energy source for internet of things devices near room temperature. In this direction, it is important to have a thermoelectric material with high thermoelectric performance. Cesium tin triiodide (CsSnI3) single crystal perovskite has shown high value of Seebeck coefficient and ultra low thermal conductivity which are necessary conditions for high thermoelectric performance. Here, we report the thermoelectric response of CsSnI3 thin films. These films are prepared by cost effective wet spin coating process at different baking temperature. Films were characterized using X-ray diffraction and scanning electron microscopy. In our case, films baked at 130°C for 5 min have shown the best thermoelectric performance at room temperature with: Seebeck coefficient 115 μV/K and electrical conductivity 124 S/cm, thermal conductivity 0.36 W/m·K and figure of merit ZT of 0.137.