This study aims to determine the maximum possible energy conversion efficiency of visibly transparent solar cells using the detailed balance limit (also known as the Shockley-Queisser limit) and compare it to the efficiency of traditional single-junction solar cells. To achieve this, a new optical nanoantenna has been designed to absorb incoming light selectively, enhancing the average visible transmission while maintaining high absorption in the infrared and UV regions. The color appearance of the antennas has also been evaluated through colorimetrical characterization. Our findings indicate that it is possible to achieve high average visible transparency and energy conversion efficiency of over 80 and 18%, respectively, by carefully selecting semiconductor materials. Such solar cells are versatile enough to be integrated seamlessly into smart windows, agrivoltaic concepts in open and protected cultivation, mobile devices, and appliances without compromising their appearance or functionality. The dimensions and optics of the proposed antennas and visibly transparent solar cells have been thoroughly discussed.

Background: In the last decade, there has been much interest in the area of solid polymer electrolyte (SPE) to address the issues of electrolyte leakage and evaporation in electrochromic devices (ECD). ECD is a state-of-the-art technology having the ability to change from transparent state to opaque state under the influence of a small applied voltage for energy saving applications. Methods: In this work, tungsten oxide (WO3) films were fabricated via the sol-gel spin-coating method. Subsequently, ECDs were assembled based on SPE and liquid polymer electrolyte (LPE), respectively using indium doped tin oxide (ITO) coated glass as conducting electrodes and WO3 films as working electrode. Results: Cyclic voltammetry (CV) results revealed reduced ionic conductivity of conducting ions in SPE based ECD (SECD) owing to increased viscosity by addition of PMMA. However, lesser time was required for the colouration process. LPE based ECD (LECD) showed higher colouration efficiency (CE) compared to its SECD counterpart. This is attributed to its larger optical modulation. Conclusions: This work presents a comparison between the performance of LECD and SECD in terms of electrochromic (EC) and optical properties. They were analysed through CV, chronoamperometry (CA) and ultraviolet-visible (UV-Vis) spectrophotometer. Furthermore, this work provides an insight on the employment of solid-state electrolytes in ECDs in view of the persistent leakage and evaporation problems in ECD implementation.

In this study, optical multispectral sensors based on perovskite semiconductors have been proposed, simulated, and characterized. The perovskite material system combined with the 3D vertical integration of the sensor channels allow for realizing sensors with high sensitivities and a high spectral resolution. The sensors can be applied in several emerging areas, including biomedical imaging, surveillance, complex motion planning of autonomous robots or vehicles, artificial intelligence, and agricultural applications. The sensor elements can be vertically integrated on a readout electronic to realize sensor arrays and multispectral digital cameras. In this study, three- and six-channel vertically stacked perovskite sensors are optically designed, electromagnetically simulated, and colorimetrically characterized to evaluate the color reproduction. The proposed sensors allow for the implementation of snapshot cameras with high sensitivity. The proposed sensor is compared to other sensor technologies in terms of sensitivity and selectivity.

The photovoltaic performance of perovskite solar cells (PSCs) can be improved by utilizing efficient front contact. However, it has always been a significant challenge for fabricating high-quality, scalable, controllable, and cost-effective front contact. This study proposes a realistic multi-layer front contact design to realize efficient single-junction PSCs and perovskite/perovskite tandem solar cells (TSCs). As a critical part of the front contact, we prepared a highly compact titanium oxide (TiO2) film by industrially viable Spray Pyrolysis Deposition (SPD), which acts as a potential electron transport layer (ETL) for the fabrication of PSCs. Optimization and reproducibility of the TiO2 ETL were discreetly investigated while fabricating a set of planar PSCs. As the front contact has a significant influence on the optoelectronic properties of PSCs, hence, we investigated the optics and electrical effects of PSCs by three-dimensional (3D) finite-difference time-domain (FDTD) and finite element method (FEM) rigorous simulations. The investigation allows us to compare experimental results with the outcome from simulations. Furthermore, an optimized single-junction PSC is designed to enhance the energy conversion efficiency (ECE) by > 30% compared to the planar reference PSC. Finally, the study has been progressed to the realization of all-perovskite TSC that can reach the ECE, exceeding 30%. Detailed guidance for the completion of high-performance PSCs is provided.

Color imaging experiment demonstrates a photochromic behavior of mixed-halide perovskites upon dark and light excitation, while the color emitted by the crystals changes from red to yellow and vice versa with the intensity of excitation light source. Unlike the photochromic property commonly observed in solution-state polymer materials, solid-state perovskite materials with photochromic behavior might open wide applications in consumer products and electronic devices. In the next part, we report on a reversible photoluminescence (PL) peak in iodide-based organic-inorganic lead halide perovskite materials under a 2-photon absorption process, while tuning the excitation wavelength. Intriguingly, two shorter wavelength peaks are visible and become prominent when the excitation photon energy is being tuned in the high energy spectrum, while laser power is remained constant. The same phenomenon of reversible PL peak is also observed in various iodine-based organicinorganic halides as well as all-inorganic perovskite single crystals and polycrystals. We attribute to the reversible PL peak phenomenon to the photoinduced structural deformation and the associated change in the optical bandgap of iodide perovskites under the femtosecond laser excitation. Our findings will introduce a degree of freedom in future research as well as adding functionalities to optoelectronic applications in these emerging perovskite materials-based devices.

Dye sensitized solar cells (DSSCs) have been in the research limelight for some years and plenty of research were devoted to the investigation of material properties for device enhancement. The electrical modeling facilitates the simulation of the device characteristics of the DSSCs. In order to develop highly efficient DSSCs, it is crucial to elucidate the electric mechanism within the cell through the electrical modeling. In this work, we propose a simplified explicit method to estimate the four parameters (photo-generated current (Iph), saturation current (Is), ideality factor (n) and series resistance (Rs)) used in the equivalent circuit by using the single diode model. By using the proposed explicit method, two series of simulated I-V curves (blocking layer and chenodeoxycholic acid additive) were generated from LTspice software by using the experiment data of current-voltage (I-V) measurements reported in our previous research. The simulated I-V curves derived from the software show good fitting to the corresponding experimental I-V curves, which demonstrate that the simplified explicit method reported here can be used to serve as an effective approach to evaluate the electrical properties of the DSSCs.

The front contact of solar cells greatly influences the optoelectronic performance of perovskite solar cells (PSCs) by controlling the coherent light propagation as well as charge transport within the device. Herein, the nanophotonic front contact consisting of multilayer nanodomes and nanoholes for high‐efficiency perovskite single‐junction and perovskite/perovskite tandem solar cells (PVK/PVK TSCs) is investigated. The optical and electrical characteristics of solar cells are investigated by conducting an advanced 3D numerical approach with the combination of finite‐difference time‐domain (FDTD) and finite‐element method (FEM) simulations embedded with the particle swarm optimization (PSO) algorithm. The numerical modeling is validated by fabricating a set of efficient PSCs, optimized to a power conversion efficiency (PCE) of 17.9%, VOC of 1.07 V, JSC of 21.8 mA cm−2 and fill factor (FF) of 77%. The nanophotonic device results in improved JSC by 10−15%, resulting from 10−15% enhanced light incoupling compared with the planar device, while also strengthening the omnidirectional capabilities at angles of illumination as high as 40°. The optimized nanophotonic front contact results in PCEs of >23% and >30% (matched JSC ≈18 mA cm−2) for single‐junction PSCs and PVK/PVK TSCs, respectively. Details of the nanophotonic front contact, device, and fabrication process are provided.

A hybrid energy harvesting system that simultaneously generates electrical energy and chemical energy with an increased overall energy conversion efficiency is designed. A photovoltaic system together with photosynthesis-executing plants forms the system. The photosynthesis-executing plants are placed directly behind or under the solar cells, but the presence of the solar cells does not affect the photosynthesis process of the plant. The spectral characteristics of the solar cells are tuned to allow for optimal plant growth. To achieve the required spectral absorption, the solar cells are tailored by using a high-band-gap (1.95 eV) mixed-halide perovskite. A guide on how to achieve an efficient hybrid energy-harvesting system is introduced. Furthermore, the suggested solar module enables a simple manufacturing process, which is consistent with the fabrication of most thin-film solar modules.

We report on the preparation and optimization of low temperature (<200 degrees C) processed TiO2 film as an electron transport layer (ETL) for high-performance perovskite solar cells (PSCs) compatible with flexible substrates. A high-quality ETL is spin-coated from hydrothermal synthesized single-phase crystalline anatase TiO2 nano particles (NPs) with an average diameter of 6 similar to 10 nm. The surface of the high crystallite TiO2 NPs reveals a tendency toward interparticle necking, facilitating compact scaffolds, resulting in PSCs with high power conversion efficiencies (PCEs). The influence of low and high temperature treated TiO2 ETL on the device performance is studied. The best planar device fabricated in superstrate configuration (sup-C) exhibits a PCE of 17.1% with a J(SC) of 20.3 mA/cm(2). The PCE can be increased by similar to 25%, up to 23%, by moving from planar architecture in sup-C to the textured solar cell in substrate configuration (sub-C). The PSC covered with a nanophotonicstructured front contact allows gaining 8% and 15% on V-OC and J(SC), respectively, where 2/3 of J(SC) gain is attributed to improved light incoupling, while the remaining 1/3 is due to increased diffraction at long wavelengths. The optical and electrical characteristics of the devices are investigated by 3D finite-domain time domain (FDTD) and finite element method (FEM) rigorous simulations. Detailed guidelines on the nanophotonic design are provided.

We present a strategy for photon management in front contact of perovskite solar cells (PSCs) compatible with tandem and flexible PSCs capable of optimizing device characteristics while providing an additional mechanism to overcome excessive focusing that affects the device's photostability. Rigorous validation of the numerical modeling used was performed by fabricating PSCs in a superstrate configuration optimized to reach high performance, ECE = 17.4%, V-OC = 1.02 V, J(SC) = 22.3 mA/cm(2), and FF = 77%. These 3D electromagnetic simulations combining the finite-difference time-domain (FDTD) and finite element method (FEM) techniques provide detailed insights of the photonic and electrical effects in PSCs. Numerical optimization of the dual capabilities of a novel nanostructured front contact enables control of the absorbed power density distribution to maximize efficiency while simultaneously minimizing nanostructure-related sub-wavelength focusing effects. In-depth analysis of the proposed photon management reveals enhanced electrical characteristics to maximize charge extraction leading to J(SC) enhancements of similar to 15 that can be as high as 33% for ultra-thin active layers suitable for flexible PSCs compared to planar PSCs performance. Furthermore, we show that the design of the front contact layer's nanostructure enables control of the power density distribution in the device to engineer PSCs' photostability without compromising performance enhancements afforded by the nanophotonic front contact. Details of the nanophotonic front contact, device, and fabrication process are provided.

Image sensing technology has a great impact on our daily life as well as the entire society, such as health, safety and security, communication systems, and entertainment. The conventional optical color sensors consist of side by side arranged optical filters for three basic colors (blue, green, and red). Hence, the efficiency of such optical color sensors is limited by only 33%. In this study, a vertically stacked color sensor is investigated with perovskite alloys, which has the potential to provide the efficiency approaching 100%. The proposed optical sensor will not be limited by color Moire error or color aliasing. Perovskite materials with suitable bandgaps are determined by applying the energy shifting model and the optical constants are used for further investigations. Quantum efficiencies and spectral responsivities of the described color sensors are investigated by three-dimensional electromagnetic simulations. Investigated spectral sensitivities are further analyzed for the

The tunable bandgap properties of perovskite materials allow attaining highly efficient tandem solar cells. An optimum bandgap for tandem solar cells can be reached by tuning the composition of halide elements in the perovskite material systems. However, realizing efficient tandem solar cells is complex, which needs a considerable understanding of device geometry and associated materials as compared to the single-junction solar cells. In this study, planar perovskite/perovskite and perovskite/silicon tandem solar cells are designed by considering realistic interface morphologies and device geometries, which can exhibit energy conversion efficiencies ~30%. Herein, the optics and optimization of solar cells are investigated by finite-difference time-domain (FDTD) simulations in three dimensions. Contact materials used in the nanophotonic design of tandem solar cells were prepared by the atomic layer deposition (ALD) of zinc oxide films. Investigated solar cells are compared in terms of their quantum efficiencies, short-circuit current densities and calculated power densities. A detailed discussion on nanophotonic device designs is provided.

Perovskite/perovskite tandem solar cells (Pk/Pk TSCs) have a substantial potential to outperform the ShockleyQueisser limit of single-junction solar cells. However, optimum material bandgap selection and device processability impede the progress in acquiring efficient Pk/Pk TSCs. The choice of charge transport/contact materials additionally has a significant influence on the photovoltaic performance of Pk/Pk TSCs. Hence, the actual fabrication of a two-terminal Pk/Pk TSC becomes tricky, which requires a detailed understanding of the underlying optical and electrical properties of the device. In this study, a wide bandgap (similar to 1.72 eV) lead iodinebromide (Pb-I-Br) and a narrow bandgap (similar to 1.16 eV) tin lead-iodide (Sn-Pb-I) perovskite absorbers are considered as potential sub-cells for realizing highly efficient planar Pk/Pk TSCs. Furthermore, energetically associated hole and electron selective contacts are prepared by atomic layer deposition (ALD) of metal oxides. The optics of solar cells is investigated by three-dimensional finite-difference time-domain (FDTD) optical simulations, and finite element method (FEM) electrical simulations are exploited to determine realistic photovoltaic performance parameters. A comprehensive study is carried out to provide a complete guideline for the realization of energy conversion efficiency exceeding 30% in Pk/Pk TSCs.

In this study, a high-quality TiO2 compact layer (CL) is prepared by Spray Pyrolysis Deposition (SPD), which is employed as a potential ETL for the realization of PSCs. To optimize the ETL, the thickness of the TiO2-CL is varied from 20 nm to 200 nm with a step size of 20 nm, where the photovoltaic performance of each is systematically computed. The optics of the solar cell is investigated by 3D finite-difference time-domain simulations, where electrical parameters are analyzed through finite element method simulations. The optimized thickness of the TiO2-CL ETL exhibits a maximum energy conversion efficiency of 19.46%. Detailed guidelines for the optimization process and device design are provided.

Dr. M. Shahiduzzaman Nanomaterials Research Institute (NanoMaRi) Kanazawa University Kakuma, Kanazawa 920-1192, Japan Dr. M. A. Islam[++], Prof. N. Amin Institute of Sustainable Energy Universiti Tenaga Nasional (@The National Energy University) Jalan IKRAM-UNITEN Kajang, Selangor 43000, Malaysia Dr. Y. Ishikawa Graduate School of Materials Science Department of Materials Science Aoyama Gakuin University 4 Chome-4-25 Shibuya, Shibuya City, Tokyo 150-8366, Japan Prof. Y. Uraoka Graduate School of Materials Science Nara Institute of Science and Technology 8916-5 Takayama, Ikoma, Nara 630-0192, Japan Prof. D. Knipp Geballe Laboratory for Advanced Materials Department of Materials Science and Engineering Stanford University Stanford, CA 94305, USA E-mail: dknipp@stanford.edu DOI: 10.1002/smtd.202000454

Color image sensing by a smartphone or digital camera employs sensor elements with an array of color filters for capturing basic blue, green, and red color information. However, the normalized optical efficiency of such color filter-based sensor elements is limited to only one-third. Optical detectors based on perovskites are described, which can overcome this limitation. An efficient color sensor design has been proposed in this study that uses a vertically stacked arrangement of perovskite diodes. As compared to the conventional color filter-based sensors, the proposed sensor structure can potentially reach normalized optical efficiency approaching 100%. In addition, the proposed sensor design does not exhibit color aliasing or color Moiré effects, which is one of the main limitations for the filter-based sensors. Furthermore, up to our knowledge, for the first time, it could be theoretically shown that both vertically arranged sensor and conventional color filter-based sensor provide almost comparable color errors. The optical properties of the perovskite materials are determined by optical measurements in combination with an energy shift model. The optics of the stacked perovskite sensors is investigated by threedimensional finite-difference timedomain simulations. Finally, colorimetric characterization was carried out to determine the color error of the sensors.

Photon management of perovskite solar cells (PSCs) is studied by the use of nanohole front contact, which allows improving the JSC of the PSC by providing an improved light incoupling. The front contact integrated with spherical nanocone shaped holes represent a refractive index grating allowing for light incoupling approaching unity while minimizing reflection losses. Besides, the front contact has a comparable refractive index (n~2.5) with the perovskite absorber, which minimizes the front reflections in PSC. Optics and optimization of front contact and solar cell are investigated by three-dimensional (3D) finite-difference time-domain (FDTD) simulations whereas finite element method simulations are used to study the electrical response of the device. Investigations reveal a maximum light incoupling enhancement of 10~12% for the optimized PSC, leading to 10 to 27% JSC enhancement with respect to the planar reference PSC.

The necessity of thin and highly doped metal oxide films is discussed for realizing efficient perovskite single and perovskite/silicon tandem solar cells.

The short-circuit current density and energy conversion efficiency of single-junction perovskite and perovskite/perovskite tandem solar cells can be increased by photon management. In this study, optical metasurfaces were investigated as potential light trapping structures oppose to commonly used pyramidal surface textures. Herein, metal oxide-based non-resonant metasurfaces were investigated as potential light-trapping structures in perovskite solar cells. The zinc oxide nanowire-based building blocks of the metasurface can be prepared by a templated electrodeposition through a mask of resist. The phase of the incident light can be controlled by the edge length of the subwavelength large zinc oxide nanowires. An array of zinc oxide nanowires was prepared and characterized in the current study. Three-dimensional (3D) finite-difference time-domain (FDTD) optical simulations were used to compare solar cells covered with non-resonant metasurfaces with commonly used light trapping structures. As compared to the solar cells covered with zinc oxide pyramid surface texture, solar cells with the integrated non-resonant metasurfaces exhibit almost identical quantum efficiencies and short-circuit current densities. Investigations of such metasurfaces will not only improve the photon absorption in perovskite solar cells but also reveal a pathway to make high-efficiency next-generation solar cells. Detailed guidelines for the realization of non-resonant metal oxide metasurfaces will be provided.