Harvesting In Solar Cells Research Articles

Enhanced SWIR Absorption in PMMA‐Coated TiN‐Based Metamaterial

AbstractAchieving highly efficient absorption in the short wavelength infrared (SWIR) spectral region is crucial for advancing numerous technologies. SWIR absorption enhances energy harvesting in solar cells, improves the sensitivity of infrared sensors, and enables precise control of thermal radiative properties in thermal emission devices. These advancements are essential for applications such as thermal imaging, night vision, and thermophotovoltaic systems. The study presents a simple, cost‐effective design of a polymer‐coated multilayer perfect absorber (MPA) metamaterial optimized for the SWIR spectral region. The proposed MPA structure is composed of four distinct layers: a top layer made of polymethyl methacrylate (PMMA) polymer, a second layer featuring arrays of circular titanium nitride (TiN) disks, a dielectric middle layer consisting of a pure zinc oxide (ZnO) film, and a bottom metallic layer formed by a thin film of TiN. The results demonstrate that the MPA achieves near‐perfect absorption, with a remarkable 99% efficiency centered at a wavelength of 1.3 µm. The absorption properties are further investigated with respect to various structural parameters to ensure better performance of the absorber. These absorbers hold great promise for applications in energy absorption, infrared sensing, thermal emission, and related fields.

A comprehensive investigation of the synthesis, spectral, DFT, and optical properties of a novel oxadiazolyl-pyrano[3,2-c]quinoline for photosensor applications

The condensation reaction of pyranoquinoline-3-carbaoxldehyde 1 with benzohydraide afforded hydrazone 2 which upon oxidative cyclization yielded 6-ethyl-4‑hydroxy-3-(5-phenyl-1,3,4-oxadiazol-2-yl)-2H-pyrano[3,2-c]quinoline-2,5(6H)‑dione (EHPOPQ, 3). The DFT and B3LYP/6–311++G(d,p) basis set were used to compute the optimized molecular geometry. The global reactivity descriptors were examined and showed that hydrazone 2 exhibited high softness while aldehyde 1 had more electronegativity and high global electrophilicity. Subsequently, the reactive sites of the present compounds were located by tracing the MEP map. The GIAO method was used to calculate the 1H and 13C NMR. The current comprehensive investigation of the novel (EHPOPQ) reveals its significant potential for applications in nonlinear optics (NLO) and photovoltaics. Through high-level computational methods, EHPOPQ has an exceptionally high first hyperpolarizability (βtot) of 950 × 10−30 esu, which is substantially higher than that of the conventional NLO material urea. This high βtot value suggests that EHPOPQ could dramatically enhance the efficiency and performance of NLO devices such as frequency converters and optical modulators. In parallel, the detailed spectroscopic analysis of EHPOPQ's optical properties provided critical insights for photovoltaic applications. The optical band gap was measured to be 3.07 eV, indicating a direct band gap transition suitable for efficient light harvesting in solar cells. Additionally, dispersion parameters were carefully analyzed, which are essential for understanding the interaction of light with the material. The experimental characterization of EHPOPQ-based photovoltaic devices showed promising results. Current-voltage (J-V) measurements under varying illumination intensities revealed significant enhancements in the device's short-circuit current (from 1.2 µA to 4.3 µA) and open-circuit voltage (from 0.25 V to 0.47 V) as light intensity increased. These findings demonstrate the material's heightened photoresponsivity and suggest its potential as an efficient light conversion material for solar energy applications. These specific findings underline the importance of EHPOPQ in advancing both NLO and photovoltaic technologies, offering a pathway to more efficient and effective devices.

Cu metal nanoparticles in transparent electrodes for light harvesting in solar cells

We report on copper nanoparticles produced by laser ablation, in acetone and methanol, from a Cu target using a 1064 nm nanosecond pulsed laser. The morphology, size, structure and chemical composition of the nanoparticles are investigated as a function of the solvent employed. Different analyses confirm the metallic nature of the nanoparticles, without amorphous carbon or copper oxides shells. Then, the nanoparticles are embedded between two transparent electrodes, aluminium-doped zinc oxide (AZO) and zirconium-doped indium oxide (IZrO) as top and bottom layers, respectively. The Glass/IZrObott/Cu nanoparticles/AZOtop structures are synthesized and optimized as plasmonic and conductive structure for photovoltaic applications. Optical properties show a strong dependence on the thermal annealing at 200 °C and type of copper nanoparticles embedded in transparent electrodes. The transparent electrode with the lowest Egap limits the Egap to the whole structure. The best structure shows a mean value of transmittance in the visible-NIR range of ∼79% with an Egap of 3.43 eV and, moreover, it shows diffused transmittance between 2.5 and 6% in VIS-NIR range and a sheet resistance of 79 Ω/sq. The performances of the best structure are tested measuring the internal quantum efficiency of a tandem solar cell, getting values as high as 89%.

Fluorescent metal nanoclusters: prospects for photoinduced electron transfer and energy harvesting.

Research on noble metal nanoclusters (MNCs) (elements with filled electron d-bands) is progressing forward because of the extensive and extraordinary chemical, optical, and physical properties of these materials. Because of the ultrasmall size of the MNCs (typically within 1-3 nm), they can be applied in areas of nearly all possible scientific domains. The greatest advantage of MNCs is the tunability that can be imposed, not only on their structures, but also on their chemical, physical, and biological properties. Nowadays, MNCs are very effectively used as energy donors and acceptors under suitable conditions and hence act as energy harvesters in solar cells, semiconductors, and biomarkers. In addition, ultrafast photoinduced electron transfer (PET) can be practised using MNCs under various circumstances. Herein, we have focused on the energy harvesting phenomena of Au-, Ag-, and Cu-based MNCs and elaborated on different ways to apply them.

Crystal Chemistry, Optic and Magnetic Characterizations of a New Copper Based Material Templated by Hexahydrodiazepine.

Crystals of the new organic-inorganic material (DAP-H2)[CuBr4] (1); (DAP = hexahydrodiazepine (C5H14N2)) were successfully synthesized by slow evaporation and characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermal analysis, UV-Vis-NIR diffuse reflectance spectroscopy, and magnetic measurements. X-ray investigation demonstrates that 1 crystallizes in the monoclinic space group C2/c. The supramolecular crystal structure of 1 is guided by several types of hydrogen bonding which connect anions and cations together into a three-dimensional network. The optical band gap was determined by diffuse reflectance spectroscopy to be 1.78 eV for a direct allowed transition, implying that it is suitable for light harvesting in solar cells. The vibrational properties of this compound were studied by infrared spectroscopy, while its thermal stability was established by simultaneous TGA-DTA from ambient temperature to 600 °C. The study of the photoresponse behavior of an optoelectronic device, based on (C5H14N2)[CuBr4], has shown a power conversion efficiency (PCE) of 0.0017%, with J sc = 0.0208 mA/cm2, V oc = 313.7 mV, and FF = 25.46. Temperature dependent magnetic susceptibility measurements in the temperature range 1.8-310 K reveal weak antiferromagnetic interactions via the two-halide superexchange pathway [2J/k B = -8.4(3) K].

INFLUENCE OF SILVER NANOPARTICLES ON TOTAL ABSORPTION FLUXES OF METHYL AMMONIUM LEAD TRI-IODIDE PHOTOCELL

Plasmonic nanoparticles exhibit a great ability to dramatically improve photon harvesting in solar cells. They provide an exceptionally very innovative way of transforming the solar cell and photovoltaic cell industries. In photovoltaic cell research, nano-plasmonics especially noble metal nanoparticles have emerged as a new frontier runner plasmons to be incorporated in photovoltaic structures. These nano plasmons concentrate photons and channel them inside a perovskite layer. However, challenges on its effectiveness have emerged and need to be addressed. These challenges includes the loss in absorption fluxes, increased light trapping band, developing inexpensive fabrication techniques, scaling plasmonics into manufacturing levels and integrating them into perovskite active nanostructures. In this paper, we address the challenge posed by low total absorption fluxes and decreased total enhancement across the whole solar spectrum using silver nanoplasmonics to improve its total absorption fluxes. We therefore document a numerical analysis of total absorption enhancements of a model CH3NH3PbI3 perovskite photocell whose active absorber layer is embedded with spherical plasmonic silver nanoparticles of different diameters at different array spacing. It is still unknown to what extent the organic cation (framework) affects the optical and electronic properties of CH3NH3PbI3 perovskites. Further, there a number of questions that have been raised in relation to the inorganic framework or lattice though computational has suggested that CH3NH3PbI3 is influenced by different geometric parameters related to CH3NH3+ on its nitrogen K-edge (or the nitrogen 1s-orbital electrons). Therefore, new ways in which the organic cation can interact with the inorganic Pb–I lattice is believed to affect its XA spectrum and therefore its electronic structure. It has been suggested that hybridized CH3NH3+ levels in the (lead-and-iodide dominated) valence band appear to dominate in CH3NH3PbI3 crystals and the band gap in CH3NH3PbI3 can change due to the rotation of the CH3NH3+ cation, mostly by affecting the conduction band. The influence of particle size, array spacing and location is analyzed numerically and discussed in a realistic system. Results revealed that when silver nanoparticles are integrated into a CH3NH3PbI3 perovskite layer, total solar absorption enhancement increases by 8% in the infrared (IR) and by 48 % in the far-infrared (far-IR) spectra in layers of 135 nm thicknesses at minimum array spacing and maximum diameter. It was concluded that the total absorption enhancement can be improved by reinforcement from a plasmonic near-field influenced by its total cross sectional scattering effects. In this process absorption in the IR and far IR spectra is influenced in the CH3NH3PbI3 perovskite layer.

Selenium-containing bodipy dyes as photosensitizers

“Boron-dipyrromethenes or BF2dipyrrins (BODIPY)“ are high fluorescent dyes and it is applicable in many fields for their attractive photochemical and photophysical properties. BODIPY has different sites of potential for its functional groups, where these groups can be functionalized and introduced. BODIPY can help in building blocks for the synthesization of the desired derivatives of BODIPY. The paper presents a series of existing literature on the given topic to obtain the required information for further studies. It presents that BODIPY could be utilized to wash the living cells for sensing the temperature and fluorescence imaging, in addition to that it also presents an increase of water solubility for increasing the efficiency. Different methods are utilized for the preparation of Selenium BODIPY, 2–1 pot procedure that follows the DDQ oxidation process. One of the most commonly used approaches for synthesis is the pyrrole condensation with aldehydes and the reaction within it is performed with the help of chromatography. BODIPY dyes are able to note their absorption band and stoke shifts for functionalized polymers for systems for light harvesting in solar cells. The dyes holds fluorescence molecules with relevant chemical and physical characteristics for both thermal and chemical stabilities. The substance possess low polarity and pH elements with low sensitivity and PDT as a photosensitizer. The applications of BODIPY hold sharp absorption and visible fluorescence, easy to use synthetization, ”high absorption coefficient“, and stable chemical and thermal properties. Lastly, it can be seen that BODIPY are able to produce dyes quickly and easily.

Carbon Nanodots from an In Silico Perspective.

Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications.

Thioacetamide-derived nitrogen and sulfur co-doped carbon quantum dots for “green” quantum dot solar cells

To make quantum dot sensitized solar cells (QDSCs) competitive, a power conversion efficiency (PCE) comparable to other developing solar cells is required. Significant attention has been paid to undoped or nitrogen (N) doped carbon quantum dots (N-CQDs) for use as sensitizers or light harvesters in solar cells. However, to our knowledge, the nitrogen and sulfur (S) co-doped CQDs (N, S-CQDs) have never been used as the absorbing layer alone. In the present work, we synthesize nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) from a single precursor thioacetamide (TA), via a hydrothermal method. The as-prepared N, S-CQDs were employed as a “green” photoactive layer in TiO2 film, as photoanode. The solar cell delivered an open-circuit voltage (Voc) of 0.43 V, short-circuit current (Jsc) of 0.61 mA/cm−2, fill factor (FF) of 52 %, and PCE of 1.36%; highest among all the carbon-based QDSCs. Moreover, Device-NS showed more stability over 48 h compared to Device-C and Device-N. Undeniably, the achieved PCE is not satisfactory; however, the upgraded device fabrication and structural design may improve PCE and current densities while sustaining the high open-circuit voltage. This study demonstrated the potential application of N, S-CQDs for low-cost, “green” quantum dot solar cell applications.

Analysis of multilayer convective flow of a hybrid nanofluid in porous medium sandwiched between the layers of nanofluid

AbstractAgBr acts as a good sensitizer for titanium oxide, hence TiO2–AgBr nanoparticles exhibit high photocatalytic activity which helps decompose methyl orange under visible light irradiation. Methyl orange is a chemical compound that is hard to degrade and has high stability. It is photoreactive and can capture photons from the sun and is highly used as a light harvester in solar cells, hence, it is used in solar applications. In view of this, the present article deals with the analysis of heat transfer in a multilayer flow of two immiscible nanofluids in a vertical channel that finds application in the fields of solar reactors, electronic cooling, and so on. The mathematical model involving the effect of thermal radiation and the presence of heat source is in the form of a system of ordinary differential equations. This system of equations is simplified using the differential transform method‐Padé approximant and the resulting equations are solved algebraically. It is observed that the temperature of the coolant does not reach its saturation point faster due to the presence of different base fluids that differ in their thermal conductivity. This helps in maintaining the optimum temperature of the system.

Organic-quantum dot hybrid interfaces and their role in photon fission/fusion applications

Solar energy is rapidly becoming a more important aspect in today's energy systems, and solar cells are playing a major role in this shift. However, to further boost the efficiency of conventional solar cells, fundamental thermodynamic limits must be overcome. Photon fission and photon fusion, also known as photon downconversion and photon upconversion, are gaining increasing attention as a means to improve solar energy harvesting in solar cells by overcoming thermalization and transmission losses, respectively. Important developments in these fields include the use of organic–inorganic hybrid materials that can leverage the advantages of each material. In this review, we look at the development of organic–quantum dot (QD) hybrid materials and their use as components of photon fission and fusion systems. We put a particular focus on the triplet energy transfer across these organic–inorganic hybrid interfaces and how this understanding has been developed. In the later part of the review, we focus on the recent examples of these hybrid materials as crucial components in solar energy harvesting applications based on triplet–triplet annihilation photon upconversion or singlet-fission–based photon multiplication. By highlighting the most relevant discoveries toward understanding and designing organic-QD hybrid interfaces for photon fission and fusion applications, we establish a starting point for researchers to continue moving this research field forward toward practical applications.

Fabrication of Perovskite Solar Cells with Digital Control of Transparency by Inkjet Printing.

Semitransparency is an attractive and important property in solar cells since it opens new possibilities in a variety of applications such as tandem cell configuration and building-integrated photovoltaics. Metal halide perovskite has the optimal properties to function as the light harvester in solar cells and can be made as a thin film, while its chemical composition can change its band gap. However, achieving high transparency usually compromises the solar cell's efficiency. Here we report on a unique approach to fabricating semitransparent perovskite solar cells that does not rely on their composition or their thickness. The approach is based on a scalable process, inkjet printing of arrays of transparent pillars, which are composed of inert photopolymerizable liquid compositions and are partly covered by the perovskite. This material can be printed at specific locations and array densities, thus providing a digital control of both the transparency and efficiency of the solar cells. The new semitransparent device structure shows 11.2% efficiency with 24% average transparency without a top metal contact. Further development including deposition of a transparent contact enabled the fabrication of fully semitransparent devices with an efficiency of 10.6% and average transparency of 19%.

Optical studies of semiconductor perovskite nanocrystals for classical optoelectronic applications and quantum information technologies: a review

Semiconductor perovskite films are now being widely investigated as light harvesters in solar cells with ever-increasing power conversion efficiencies, which have motivated the fabrication of other optoelectronic devices, such as light-emitting diodes, lasers, and photodetectors. Their superior material and optical properties are shared by the counterpart colloidal nanocrystals (NCs), with the additional advantage of quantum confinement that can yield size-dependent optical emission ranging from the near-UV to near-infrared wavelengths. So far, intensive research efforts have been devoted to the optical characterization of perovskite NC ensembles, revealing not only fundamental exciton relaxation and recombination dynamics but also low-threshold amplified spontaneous emission and novel superfluorescence effects. Meanwhile, the application of single-particle spectroscopy techniques to perovskite NCs has helped to resolve a variety of optical properties for which there are few equivalents in traditional colloidal NCs, mainly including nonblinking photoluminescence, suppressed spectral diffusion, stable exciton fine structures, and coherent single-photon emission. While the main purpose of ensemble optical studies is to guide the smooth development of perovskite NCs in classical optoelectronic applications, the rich observations from single-particle optical studies mark the emergence of a potential platform that can be exploited for quantum information technologies.

Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells

Summary The quaternary chalcogenide halides of group IV and V elements have attracted much attention due to their interesting semiconducting properties as well as a suitable band gap for solar cells. Here, for the first time, we report on solar cells using tin-antimony sulfoiodide (Sn2SbS2I3). Sn2SbS2I3 solar cells were fabricated using a chemical single-step deposition process with a solution containing a SbCl3-thiourea complex and SnI2 with the configuration of TiO2 and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-enzothiadiazole)] as the electron- and hole-transporting layers, respectively. The best-performing cell exhibits a power conversion efficiency of 4.04% under the illumination of standard AM 1.5G conditions (100 mW cm−2). These unencapsulated cells exhibited good stabilities at 80% relative humidity, 85°C in air, and under illumination, respectively. These results provide guidelines for fabrication of lead-free heteroleptic perovskite solar cells by hosting divalent or combinations of monovalent and trivalent metal cations.

Contribution to sustainable and environmental friendly non-toxic CZTS solar cell with an innovative hybrid buffer layer

Due to non-toxicity and earth abundancy of raw materials, CZTS grabbing the attention of researchers to make it highly efficient and cost-effective solar cell harvesting. Thin-film CZTS based solar cell of higher efficiency reported with conventional CdS layer. Toxicity of Cd influences to reduce the thickness of the CdS buffer layer without compromising with the efficiency. The present paper deals with CdS/In2S3 and CdS/ZnS hybrid buffer layer which is more efficient than the solar cell using only the CdS buffer layer. The reduced thickness of the CdS layer in CZTS/CdS/In2S3/ZnO: Al and CZTS/CdS/ZnS/ZnO: Al structures have been optimized by using SCAPS-1D simulation software. This study reveals that there is an enhancement in the performance of solar cells from η = 15.68% with CdS to η = 16.52% with CdS/In2S3 and η = 15.81% with CdS/ZnS hybrid buffer layer. Variation in PV parameters with a variation of the thickness of the buffer and absorber layer has been optimized. The acceptor density of CZTS/CdS/In2S3 and CZTS/CdS/ZnS was varied and results have been optimized. A numerical study of both structures on the photovoltaic performance of CZTS solar cells has been done by using SCAPS-1D simulation software.

Atomic layer deposition of amorphous antimony sulfide (a-Sb2S3) as semiconductor sensitizer in extremely thin absorber solar cell

Atomic layer deposition of amorphous antimony sulfide (a-Sb2S3) is demonstrated with an alternating exposure of tris(dimethylamino)antimony (TDMASb) and hydrogen sulfide (H2S) at 150 °C in a custom-built viscous flow reactor. Growth mechanism and deposition chemistry are investigated by in situ quartz crystal microbalance and in situ Fourier Transform Infrared spectroscopy. Reaction hypothesis facilitating the binary reaction is established by quantum mechanical density functional theory calculations that essentially support the experimental findings. The developed material is used as a photon harvester in solar cells under extremely thin absorber configuration, with TiO2 and Spiro-OMeTAD as electron and hole transporting layers, respectively. Investigation of charge injection properties with surface photovoltage spectroscopy reveals low but non-negligible density of interfacial (sensitizer/TiO2) electronic defects. The conventional viscous flow reactor configuration is modified to showerhead-type reactor configuration to achieve better uniformity and conformality of a-Sb2S3 on highly porous TiO2 scaffolds. a-Sb2S3 device performance is optimized to achieve the highest power conversion efficiencies of 0.5% while annealed crystalline c-Sb2S3 device reaches power conversion efficiencies of 1.9% under 1 sun illumination.

Realizing Stable Artificial Photon Energy Harvesting Based on Perovskite Solar Cells for Diverse Applications.

As the fastest developing photovoltaic device, perovskite solar cells have achieved an extraordinary power conversion efficiency (PCE) of 25.3% under AM 1.5 illumination. However, few studies have been devoted to perovskite solar cells harvesting artificial light, owing to the great challenge in the simultaneous manipulation of bandgap-adjustable perovskite materials, corresponding matched energy band structure of carrier transport materials, and interfacial defects. Herein, through systematic morphology, composition, and energy band engineering, high-quality Cs0.05 MA0.95 PbBrx I3- x perovskite as the light absorber and Nby Ti1- y O2 (Nb:TiO2 ) as the electron transport material with an ideal energy band alignment are obtained simultaneously. The theoretical-limit-approaching record PCEs of 36.3% (average: 34.0 ± 1.2%) under light-emitting diode (LED, warm white) and 33.2% under fluorescent lamp (cold white) are achieved simultaneously, as well as a PCE of 19.5% (average: 18.9 ± 0.3%) under solar illumination. An integrated energy conversion and storage system based on an artificial light response solar cell and sodium-ion battery is established for diverse practical applications, including a portable calculator, quartz clock, and even environmental monitoring equipment. Over a week of stable operation shows its great practical potential and provides a new avenue to promote the commercialization of perovskite photovoltaic devices via integration with ingenious electronic devices.

Analysis of highly efficient perovskite solar cells with inorganic hole transport material

Organo-halide perovskites in planar heterojunction architecture have shown considerable promise as efficient light harvesters in solar cells. We carry out a numerical modeling of a planar lead based perovskite solar cell (PSC) with Cu2ZnSnS4 (CZTS) as the hole transporting material (HTM) using the one-dimensional solar cell capacitance simulator (SCAPS-1D). The effects of numerous parameters such as defect density, thickness, and doping density of the absorber layer on the device performance are investigated. The doping densities and electron affinities of the electron transporting material (ETM) and the HTM are also varied to optimize the PSC performance. It has been observed that a thinner absorber layer of ∼220 nm with a defect density of 1014 cm−3 compared to the reference structure improves the device performance. When doping density of the absorber layer increases beyond 2 × 1016 cm−3, the power conversion efficiency (PCE) reduces due to enhanced recombination rate. The defect density at the absorber/ETM interface reduces the PCE as well. Considering a series resistance of 5 Ω · cm2 and all the optimum parameters of absorber, ETM and HTM layers simultaneously, the overall PCE of the device increases significantly. In comparison with the reference structure, the PCE of the optimized device has been increased from 12.76% to 22.7%, and hence the optimized CZTS based PSC is highly efficient.

Development of flexible, stable, and efficient inverted organic solar cells harvesting light in all directions

In this work, we designed low-cost, liquid-free, efficient, and highly flexible fiber-shaped inverted structure organic solar cells (FOSCs) over a flexible polyethylene terephthalate (PET) monofilament substrate. We also prepared a graphene–ZnO (G-ZnO) composite, wherein G sheets were compacted into a bunched-up structure through the binding force of Zn atoms with the C atoms of G. This composite was then utilized as a bifunctional layer i.e. electron transport and downconversion spectral in the FOSCs. The FOSCs based on the G-ZnO (D-1) demonstrated a power conversion efficiency (PCE) of 2.13% out of which 4.89% and 5% was retained after 8000 times bending and 120 h storage in ambient environmental conditions, respectively. The non-G-ZnO FOSCs (D-2) demonstrated a PCE of 1.78% and retained 5% and 6% of the initial value after 6000 bends and 48 h of storage in ambient environmental conditions, respectively. This better performance of D-1 compared to that of D-2 is due to the interfacial functionalization of G-sheets and ZnO nanoparticles inside the G-ZnO composite. Because of these interfacial chemical bonds, the G sheets were in close contact with each other and attached firmly through the ZnO molecules. As a result, these compacted G layers could serve as a strong barrier resisting the penetration of water molecules inside the device, thereby leading to an improved lifetime for the device. Additionally, the longitudinal and cross linkage of G-sheets could improve the mechanical properties of the G-ZnO composite, which in turn enhanced the flexibility of D-1. Finally, these interface functionalizations could work as linking bridges, providing an additional pathway for the transportation of free charge carriers. Therefore, D-1 demonstrated a higher Jsc by collecting a greater number of charges at the electrode compared to D-2, because the latter lacked similar functionalization.

Ultra-Low-Power Gaze Tracking for Virtual Reality

LiGaze is a low-cost, low-power approach to gaze tracking tailored to virtual reality (VR). It relies on a few low-cost photodiodes, eliminating the need for cameras and active infrared emitters. Reusing light from the VR screen, LiGaze leverages photodiodes around a VR lens to measure reflected screen light in different directions. It then infers gaze direction by exploiting the pupil's light absorption property. The core of LiGaze is to deal with screen light dynamics and extract changes in reflected light related to pupil movement. LiGaze infers a 3D gaze vector on the fly using a lightweight regression algorithm. Compared to the eye tracker of an existing VR headset (FOVE), LiGaze achieves 6.3° and 10.1° mean within-user and cross-user accuracy. Its sensing and computation consume 791 W in total and thus can be completely powered by a credit card-size solar cell harvesting energy from indoor lighting. LiGaze's simplicity and ultra-low power make it applicable in a wide range of VR headsets to better unleash VR's potential.