Light Absorption In Solar Cells Research Articles

Electrochemical Self-Assembly of Cu­SCN / Dye Hybrid Thin Films and Their Optical Properties

Introduction: Combination of inorganic and organic materials offers unlimited new opportunities. While “composites” stands for their physical mixtures, “hybrids” and “inorganic/organic compounds” are especially interesting for their new functionalities, as they are achieved by self-organization due to “chemistry” among the constituents. We have established electrochemical self-assembly (ESA) of inorganic/organic hybrid thin films from one pot containing all the ingredients. 1,2) In this work, we have employed cathodic electrodeposition of CuSCN as the test bed for the ESA with various organic dyes to understand its principle and evaluated optical properties of the product thin films. Experiments: CuSCN / dye hybrid thin films were cathodically electrodeposited according to the reaction, [Cu(II)(SCN)]+ + e- → Cu(I)SCN, in the presence of various organic dyes shown in Fig. 1. Photoluminescence (PL) and PL excitation (PLE) spectra were measured between 77 and 298 K on a Horiba Fluorolog-3 equipped with a high power Xe lamp excitation source and lq. N2-cooled PMT detector. Results and discussion: Anionic xanthene dyes which afford ESA with ZnO were not successful with CuSCN except FLNCS, whereas zwitter ionic RB and all the cationic dyes yielded colorful thin films as they were loaded into CuSCN. Soft and hard, acid and base (HSAB) principle nicely explains the behavior of FLNCS, as its –NCS is soft Lewis basic, finding stable coordination to soft Lewis acidic Cu(I) site of CuSCN, just like the hard –COO- being good with hard Zn(II) of ZnO. On the other hand, partial replacement of Cu+ ions with cationic dyes (RB with its ammonium moiety) can account for their successful ESA. These two mechanisms were confirmed by the decrease of dye loading in baths containing excess SCN− and Cu2+, respectively. RB, R6G, NB and DAST show strong PL both as their solutions and in solid states with their PLEs nicely matched with their absorption spectra, while that of the hybrid thin films was totally quenched except for DAST (CuSCN/DAS hybrid thin film). The energy diagram drawn for the energy levels of individual components suggest hole transfer from HOMO of photoexcited organic chromophore to valence band of inorganic CuSCN, except for NB. Hybridization of NB with CuSCN might have altered its energetic structure to exhibit photo-induced carrier generation of the hybrid thin films, thus suggesting usefulness of the hybrid thin films with RB, R6G and NB as light absorbers in solar cells. On the other hand, the DAS+ chromophore exhibits PL even when it is loaded into CuSCN, with its energy in between solution (= monomer) and powder of DAST. While PL of solution and powder become sharp, blue-shifted and intensified at 77 K, as typically expected by exciton confinement, that of the hybrid film is red-shifted and not much intensified, suggesting a strong excitonic interaction with CuSCN to offer a new type of luminescent material.

Morphology‐Tailored Halide Perovskite Platelets and Wires: From Synthesis, Properties to Optoelectronic Devices

AbstractThe recent emergence of metal‐halide perovskites as light absorbers in solar cells has attracted lots of attention on their synthesis and properties. In particular, low‐dimensional metal‐halide perovskites like platelets and wires are expected to regulate their optical and electrical properties in reference to bulk counterparts as a result of quantum confinement and anisotropy. In this review, first, the recent solution‐ and vapor‐based approaches on synthesizing metal‐halide perovskite platelets and wires are highlighted. Then, their optical and electrical properties along with application in photonics and optoelectronics such as lasers, light emitting diodes, photodetectors, and phototransistors are discussed. At last, the importance of such perovskite platelets and wires on improving material stability and transport properties is emphasized, and potential integration of perovskites with other low‐dimensional materials in multifunctional systems is proposed.

An Optimal Au Grating Structure for Light Absorption in Amorphous Silicon Thin Film Solar Cell

Effect of different gold (Au) grating structures on light absorption in solar cell is investigated by finite elemental analysis using COMSOL multiphysics-RF module. The geometry of the solar cell consists of a 50-nm Au film on the substrate of amorphous silicon (a-Si). An optimum value of the slit width (w) of the Au grating has been obtained whereas periodicity of the grating structure remained the same. The periodicity in the grating device was chosen in such a way that the excitation of the surface plasmon polritons (SPPs) lies in the IR or NIR region where most of the spectrometers work well in practical life. Far-field transmission spectra were extracted from the grating device when illuminating with p-polarized light through the substrate side. Near-field plots of the Fano resonance (dip) associated with the excitation of the surface plasmon polritons (SPPs) were carefully examined to understand the underlying physics. It was deduced from the results that a grating device with slit width of 250–350 nm is the most efficient which reveals the fact that such device offers intermediate scattering from the grating structure and supports fundamental plasmonic mode. Hence, such devices absorb more light being most efficiently and find application in solar cell.

Design Strategy for Improving Optical and Electrical Properties and Stability of Lead-Halide Semiconductors.

Broad absorption, long-lived photogenerated carriers, high conductance, and high stability are all required for a light absorber toward its real application on solar cells. Inorganic-organic hybrid lead-halide materials have shown tremendous potential for applications in solar cells. This work offers a new design strategy to improve the absorption range, conductance, photoconductance, and stability of these materials. We synthesized a new photochromic lead-chloride semiconductor by incorporating a photoactive viologen zwitterion into a lead-chloride system in the coordinating mode. This semiconductor has a novel inorganic-organic hybrid structure, where 1-D semiconducting inorganic lead-chloride nanoribbons covalently bond to 1-D semiconducting organic π-aggregates. It shows high stability against light, heat, and moisture. After photoinduced electron transfer (PIET), it yields a long-lived charge-separated state with a broad absorption band covering the 200-900 nm region while increasing its conductance and photoconductance. This work is the first to modify the photoconductance of semiconductors by PIET. The observed increasing times of conductivity reached 3 orders of magnitude, which represents a record for photoswitchable semiconductors. The increasing photocurrent comes mainly from the semiconducting organic π-aggregates, which indicates a chance to improve the photocurrent by modifying the organic component. These findings contribute to the exploration of light absorbers for solar cells.

Enhancement of Light Absorption in Photovoltaic Devices using Textured Polydimethylsiloxane Stickers.

We designed and fabricated a random-size inverted-pyramid-structured polydimethylsiloxane (RSIPS-PDMS) sticker to enhance the light absorption of solar cells and thus increase their efficiency. The fabricated sticker was laminated onto bare glass and crystalline silicon (c-Si) surfaces; consequently, low solar-weighted reflectance values were obtained for these surfaces (6.88 and 17.2%, respectively). In addition, we found that incident light was refracted at the PDMS-air interface of each RSIPS, which redirected the incident power and significantly increased the optical path length in the RSIPS-PDMS sticker which was 14.7% greater than that in a flat-PDMS sticker. Moreover, we investigated power reflection and propagation through the RSIPS-PDMS sticker using a finite-difference time-domain method. By attaching an RSIPS-PDMS sticker onto both an organic solar cell (OSC) based on a glass substrate and a c-Si solar cell, the power conversion efficiency of the OSC and the c-Si solar cell were increased from 8.57 to 8.94% and from 16.2 to 17.9%, respectively. Thus, the RSIPS-PDMS sticker is expected to be universally applicable to the surfaces of solar cells to enhance their light absorption.

Minority-carrier lifetime and photoresponse properties of B-doped p-BaSi2, a potential light absorber for solar cells

600-nm-thick B-doped p-BaSi2 layers were grown on (111)-oriented n-Si substrates by molecular beam epitaxy, and the dependences of the minority carrier lifetime τ and photoresponsivity on the hole concentration p were investigated. p was varied from 1.4 × 1016 to 3.9 × 1018 cm−3. The highest τ of 2 µs was obtained for the sample with the lowest p of 1.4 × 1016 cm−3, reaching two orders of magnitude higher than that of the sample with the highest p of 3.9 × 1018 cm−3. The low-concentration-doped sample also exhibited an excellent external quantum efficiency (EQE) as large as 80% at a wavelength of approximately 800 nm at a reverse bias voltage of 0.2 V. This value is higher than any other EQEs we have ever achieved for BaSi2, showing the great potential of p-BaSi2 as a light absorber in solar cells.

2D homologous organic-inorganic hybrids as light-absorbers for planer and nanorod-based perovskite solar cells

We present the fabrication and characterization of two dimensional (2D) perovskites (PEA)2(MA)m-1PbmI3m+1 (PEA=phenylethylammonium, MA=methylammonium, m=1,2,3) for application as light absorbers in solar cells. Films of 2D perovskite series show high stability under humid air, with band gaps decreasing with increasing m values, from 2.36eV for (PEA)2PbI4 (m=1) to 1.94eV for (PEA)2(MA)2Pb3I10 (m=3). Owning to the smaller bandgap, favorable vertical growth characteristics, and appropriate energy band structure of (PEA)2(MA)2Pb3I10, planer perovskite solar cells based on (PEA)2(MA)2Pb3I10 exhibit best cell performance. Incorporation of TiO2 nanorod arrays into (PEA)2(MA)2Pb3I7 based perovskite solar cells are further found to be useful in improving the cell performance, ascribing to the improved quality and coverage of the perovskite films, as well as the enhanced electronic contact between the perovskites and the electron transporting layer. By optimizing the TiO2 NR lengths, an efficiency of 3.72% is obtained for (PEA)2(MA)2Pb3I10 perovskite cells with 600nm-long TiO2NRs as scaffolds, which is more than a time higher than that of the planer analogue device. Our study to design 2D perovskite solar cells demonstrates the importance of material structure and device configuration for efficient solar cells, highlighting the validity of TiO2 nanorods in functionalizing 2D perovskites for photovoltaic applications.

Band gap tuning of nickelates for photovoltaic applications

Hybrid perovskites have achieved tremendous success as a light absorber in solar cells during the past few years. However, the stability issue casts shadow on their practical applications. Perovskite oxides may offer an alternative. In this study, the metal–insulator transition in perovskite neodymium nickelates (NdNiO3) is systematically tuned by adjusting the oxygen partial pressure during film growth. Room temperature insulating films with different band gaps are obtained. Testing photovoltaic cells have been prepared by combining the nickelates with Nb-doped SrTiO3, and photovoltaic performance has been optimized. Our study offers a new route for designing novel photovoltaic materials.

Increase the absorption plasm and the flow of light energy in ultra-thin films gaas solar nano-structured metal

The silicon thin film solar cells in the visible region, The low absorption which reduces its efficiency. The use of metallic nanostructures help, to increase light absorption and reduce the size of the entire structure will be. The process of light absorption in solar cells is one of the factors in improving the performance of solar cells. Silicon thin film solar cells, in the visible region, the absorption is low. Using arrays of metallic nanostructures, Semiconductors such as silicon or germanium on, Radiation absorption, a significant amount used in the top layer. Metal nanostructures for their ability to excite PLASMONS, (Collective oscillations of free electrons) are being considered. PLASMONS, surface electromagnetic waves, They are strictly limited to the field level, And that's why the border field strength is high, As a result, the surface PLASMON excitation, Square in the vicinity of heavily reinforced silicon and thus the absorption of light, The silicon layer is increased significantly. Keyword: Plasmon light energy; NANO-structured metal

Ultraviolet Plasmonic Aluminium Nanoparticles for Highly Efficient Light Incoupling on Silicon Solar Cells.

Plasmonic metal nanoparticles supporting localized surface plasmon resonances have attracted a great deal of interest in boosting the light absorption in solar cells. Among the various plasmonic materials, the aluminium nanoparticles recently have become a rising star due to their unique ultraviolet plasmonic resonances, low cost, earth-abundance and high compatibility with the complementary metal-oxide semiconductor (CMOS) manufacturing process. Here, we report some key factors that determine the light incoupling of aluminium nanoparticles located on the front side of silicon solar cells. We first numerically study the scattering and absorption properties of the aluminium nanoparticles and the influence of the nanoparticle shape, size, surface coverage and the spacing layer on the light incoupling using the finite difference time domain method. Then, we experimentally integrate 100-nm aluminium nanoparticles on the front side of silicon solar cells with varying silicon nitride thicknesses. This study provides the fundamental insights for designing aluminium nanoparticle-based light trapping on solar cells.

Effects of silver nanoparticles size and shape on light scattering

The scattering from metal nanoparticles near their localized surface plasmon resonance is a promising way to increase the light absorption in solar cells. In this article, we investigate the light scattering of silver (Ag) nanoparticles on the microcrystalline silicon (μc-Si) substrate with various sizes and shape by finite element method. The results show that large spherical particles lead to enhanced scattering efficiency, whereas reduced coupling efficiency. The scattering cross section and coupling efficiency are very sensitive to the shape of the particles. Compared with spherical particles, hemispherical and cylindrical particles show much lower and broader scattering cross section, containing two surface plasmon resonance modes, and much higher coupling efficiency at longer wavelengths. However, with the increase in the longitudinal size (or height) of the particles, the coupling efficiency decreases, especially at shorter wavelengths, due to backscattering by the longitudinal resonance mode. Finally, we simulate the absorption enhancement in μc-Si thin film solar cells by Ag nanoparticle arrays with various shape. These results will be useful for enhancing performance of the μc-Si thin film solar cells by optimizing the light-trapping design.

2D/3D perovskite hybrids as moisture-tolerant and efficient light absorbers for solar cells.

The lifetime and power conversion efficiency are the key issues for the commercialization of perovskite solar cells (PSCs). In this paper, the development of 2D/3D perovskite hybrids (CA2PbI4/MAPbIxCl3-x) was firstly demonstrated to be a reliable method to combine their advantages, and provided a new concept for achieving both stable and efficient PSCs through the hybridization of perovskites. 2D/3D perovskite hybrids afforded significantly-improved moisture stability of films and devices without encapsulation in a high humidity of 63 ± 5%, as compared with the 3D perovskite (MAPbIxCl3-x). The 2D/3D perovskite-hybrid film did not undergo any degradation after 40 days, while the 3D perovskite decomposed completely under the same conditions after 8 days. The 2D/3D perovskite-hybrid device maintained 54% of the original efficiency after 220 hours, whereas the 3D perovskite device lost all the efficiency within only 50 hours. Moreover, the 2D/3D perovskite hybrid achieved comparable device performances (PCE: 13.86%) to the 3D perovskite (PCE: 13.12%) after the optimization of device fabrication conditions.

Analytical Calculation of Energy levels of mono- and bilayer Graphene Quantum Dots Used as Light Absorber in Solar Cells

In this paper by solving Dirac equation, we present an analytical solution to calculate energy levels and wave functions of mono- and bilayer graphene quantum dots. By supposing circular quantum dots, we solve Dirac equation and obtain energy levels and band gap with relations in a new closed and practical form. The energy levels are correlated with a radial quantum number and radius of quantum dots. In addition to monolayer quantum dots, AA- and AB-stacked bilayer quantum dots are investigated and their energy levels and band gap are calculated as well. Also, we analyze the influence of the quantum dots size on their energy spectrum. It can be observed that the band gap decreases as quantum dots’ radius increases. On the other hand, increase in the band gap is more in AB-stacked bilayer quantum dots. Using the obtained relations, the band gap is obtained in each state. Comparing the energy spectra obtained from the tight-binding approximation with those of our obtained relations shows that the behavior of the energies as function of the dot size is qualitatively similar, but in some cases, quantitative differences can be seen. As quantum dots radius increases, the analytical results approach to the tight-binding method results.

Preparation and Photovoltaic Properties of Ternary AgBiS2 Quantum Dots Sensitized TiO2 Nanorods Photoanodes by Electrochemical Atomic Layer Deposition

Ternary AgBiS2 quantum dots (QDs) were assembled onto TiO2 nanorods (NRs) film for QD-sensitized solar cell (QDSSC) application by a simple electrochemical atomic layer deposition method (ECALD). Various kinds of methods such as XRD, SEM, EDX and TEM were employed to characterize the structure and morphology of the deposits. The results indicate that stoichiometric AgBiS2 QDs of cubic structure were synthesized and homogeneously anchored on the TiO2 NRs. Furthermore, the optical absorbance of AgBiS2 sensitized TiO2 NRs was greatly enhanced in visible region compared to that of bare TiO2. The QDSSCs based on the AgBiS2 sensitized TiO2 NRs photoanodes were constructed and a maximum photoconversion efficiency of 0.95% with a short-circuit current density of 4.22 mA/cm2, an open-circuit voltage of 0.53 V and a fill factor of 0.43, has been achieved. The inspiring parameters demonstrate that AgBiS2 QDs can be a prospective light absorber in solar cells.

Realistic Simulation of Metal Nanoparticles on Solar Cells

We present a strategy for simulating the scattering effect of an array of self-aggregated (SA) metal nanoparticles (NPs) on the light absorption in solar cells. We include size and shape effects of the NPs, the effect of a layered substrate and the effect of the interaction between NPs. The simulation relies on realistic characterization by SEM microscopy of the random NP arrays. Time and memory limitations of numerical approaches are overcome using semianalytical expressions. Size and shape considerations deal with truncated-sphere shapes by using a polarisability tensor. This is a development of other models leading to equivalent dipoles from the external source and the radiated fields from the rest of NPs. Once an equivalent array of 3-D dipoles is found, the total electromagnetic field and optical simulations are performed. The general trends show good agreement with experimental measurements. A critical analysis of the model is presented, and some improvement strategies are discussed for future studies.

Influences of Nanostructure Arrays on Light Absorption in Amorphous Silicon Thin-Film Solar Cells

By means of finite-difference time-domain (FDTD) numerical method, we investigate the possibility to enhance the light absorption in solar cells by employing different nanostructures. The solar cells are made of 100-nm-thick amorphous silicon (α-Si). The impacts of gold nanohole arrays, dielectric nanosphere arrays, and gold nanoparticle arrays on the light absorption are simulated, compared, and analyzed. The results show that gold nanohole arrays functioning as the back reflective layer, dielectric nanosphere arrays, and gold nanoparticle arrays can significantly enhance the light absorption for the solar cells, and the former two can increase the short-circuit current by more than 40 %, showing a great potential to improve the utilization efficiency of solar energy.

Direct Conversion of CH3NH3PbI3 from Electrodeposited PbO for Highly Efficient Planar Perovskite Solar Cells.

Organic-inorganic hybrid perovskite materials have recently been identified as a promising light absorber for solar cells. In the efficient solar cells, the perovskite active layer has generally been fabricated by either vapor deposition or two-step sequential deposition process. Herein, electrochemically deposited PbO film is in situ converted into CH3NH3PbI3 through solid-state reaction with adjacent CH3NH3I layer, exhibiting a large-scale flat and uniform thin film with fully substrate coverage. The resultant planar heterojunction photovoltaic device yields a best power conversion efficiency of 14.59% and an average power conversion efficiency of 13.12 ± 1.08% under standard AM 1.5 conditions. This technique affords a facile and environment-friendly method for the fabrication of the perovskite based solar cells with high reproducibility, paving the way for the practical application.

Broadband light trapping based on periodically textured ZnO thin films.

Transparent conductive front electrodes (TCFEs) deployed in photovoltaic devices have been extensively studied for their significance in transporting carriers, coupling and trapping the incident photons in high-performing solar cells. The trade-off between the light-transmission, electrical, and scattering properties for TCFEs to achieve a broadband improvement in light absorption in solar cells while maintaining a high electrical performance has become the key issue to be tackled. In this paper, we employ self-assembled polystyrene (PS) spheres based on a sauna-like method as a template, followed by a double-layer deposition and then successfully fabricate highly-transparent, well-conductive, and large-scale periodically-textured ZnO TCFEs with broadband light trapping properties. A sheet resistance below 15 Ω sq(-1) was achieved for the periodically-textured ZnO TCFEs, with a concomitant average transmission of 81% (including the glass substrate) in the 400-1100 nm spectral range, a haze improvement in a broadband spectral range, and a wider scattering angular domain. The proposed approach affords a promising alternative method to prepare periodically-textured TCFEs, which are essential for many optoelectronic device semiconductors, such as photovoltaic and display applications.

Numerical simulation of light absorption enhancement in microcrystalline silicon solar cells with Al nanoparticle arrays

Metal nanoparticles with low cost and high performance have good potential applications in light-trapping of solar cells. In this paper, a three-dimensional model is proposed to simulate the light absorption of microcrystalline silicon (μc-Si:H) thin film solar cells. The effects of spherical and hemispherical Al nanoparticle arrays located on the front surfaces of solar cells are investigated, and the particle radius and array period are optimized by the finite element method. The results show that the optimal Al nanoparticle arrays can enhance broadband absorption in thin film solar cells. For spherical particle arrays, the key parameter that influences light absorption in solar cells is period/radius ratio (P/R) or particle surface coverage. When P/R=4-5, the optimum integrated absorption enhancement (Eabs) is over 20% under AM1.5 illumination compared with the solar cell without nanoparticles. The value of Eabs is small and decreases with the increase of P/R when P/R>5, and Eabs is less than zero when P/RP=500 nm and R=120 nm, the spectral absorption rate as a function of wavelength shows broadband absorption including four distinct peaks, which are attributed to quadrupole plasmon resonance mode, dipole resonance mode and waveguide mode respectively according to the electric field distribution in the solar cell. For hemispherical particle arrays, the maximum value of Eabs is 24.5%, which is higher than that of the solar cell with optimized spherical particle arrays. This is due to the high coupling efficiencies of the particles, so that most of the scattered light is directly coupled into the substrate. However, the value of Eabs is very sensitive to the hemispherical particle radius. As the radius decreases, the scattering cross-section and scattering efficiency of the particle decrease dramatically. As the radius increases, the dipole plasmon resonance wavelength rapidly shifts towards longer wavelength (red shift). Both of these are detrimental to absorption enhancement of solar cells. Thus we conclude that spherical Al particle arrays are more preferable in actually fabricating the light-trapping of solar cells.

Phase-pure iron pyrite nanocrystals for low-cost photodetectors.

Earth-abundant iron pyrite (FeS2) shows great potential as a light absorber for solar cells and photodetectors due to their high absorption coefficient (>105 cm-1). In this paper, high-quality phase-pure and single crystalline pyrite nanocrystals were synthesized via facile, low-cost, and environment friendly hydrothermal method. The molar ratio of sulphur to iron and the reaction time play a crucial role in determining the quality and morphology of FeS2 nanocrystals. X-ray diffraction and high-resolution transmission electron microscopy confirm that phase-pure and single crystalline pyrite nanocrystals can be synthesized with high sulphur to iron molar ratio and sufficient reaction time. For the first time, a crystalline nanogap pyrite photodetector with promising photocurrent and UV-visible photoresponse has been fabricated. This work further demonstrates a facile route to synthesize high-quality FeS2 nanomaterials and their potential in optoelectronic applications.