Surface Of Solar Cell Research Articles

Influences of PbS Quantum Dot Layers on Power Conversion Efficiency of Single Junction GaAs Solar Cells

PbS quantum dots were coated on the surface of single junction GaAs solar cells by a drop coating method. The thickness of PbS quantum dot layer was controlled through changing the number of coating layers. The influences of PbS coating layers on characteristics of GaAs single junction solar cells were investigated through I-V characteristic measurements, optical reflectance spectra, and quantum efficiencies. The results indicated that, the short-circuit current can be improved up to 15% with two PbS coating layers. Other parameters such as Voc and FF are hardly affected by the number of PbS coating layers. Based on the results of optical reflectance spectra and quantum efficiencies, the enhancement in the short-circuit current can be attributed to the surface antireflection layer and the ability to transfer high energy photon-generated charge carriers.

CdSe/CdS core/shell in polyacrylamide polymer matrix for Quantumdots Luminescent solar concentrator

Luminescent solar concentrator (LSC) are used to enhance photoresponsivity of solar cell. The Quantumdots luminescent solar concentrator (QDLSC) consists of CdSe/CdS core/shell nanoparticles embedded in polyacrylamide polymer matrix positioned on the top surface of the silicon solar cell. This procedure improves the conversion efficiency of the bare silicon solar cell. The conversion efficiency of the solar cell has increased from 7.3% to 10.3%. this improvement is referred to the widening of the response spectral region window of the a- Si. Solar cell.

Microfiber Optic Arrays as Top Coatings for Front-Contact Solar Cells toward Mitigation of Shading Loss

Microfiber optic array structures are fabricated and employed as an optical structure overlaying a front-contact silicon solar cell. The arrays are synthesized through light-induced self-writing in a photo-crosslinking acrylate resin, which produces periodically spaced, high-aspect-ratio, and vertically aligned tapered microfibers deposited on a transparent substrate. The structure is then positioned over and sealed onto the solar cell surface. Their fiber optic properties enable collection of non-normal incident light, allowing the structure to mitigate shading loss through the redirection of incident light away from contacts and toward the solar cell. Angle-averaged external quantum efficiency increases nominally by 1.61%, resulting in increases in short-circuit current density up to 1.13 mA/cm2. This work demonstrates a new approach to enhance light collection and conversion using a scalable, straightforward, light-based additive manufacturing process.

Investigation of triphenylamine-based sensitizer characteristics and adsorption behavior onto ZnTiO3 perovskite (1 0 1) surfaces for dye-sensitized solar cells using first-principle calculation

Four different Triphenylamine-based dyes, named as TPA-1, TPA-2, TPA-3 and TPA-4 as shown below, with substituents containing different linkages, earlier described inTiO2dye-sensitized solar cells (DSSCs), are described. The dyes are examined as potential dyes for perovskite ZnTiO3 based dye sensitized solar cells (DSSCs). The simulated characteristics include: Electronic absorption spectra, light harvesting efficiency, energy of dye adsorption to the semiconductor ZnTiO3 electrode, energy level alignment and spontaneity of charge transfer across the dye interfaces with ZnTiO3 and with solution redox couple. The characteristics have been comparatively investigated for all dyes. The absorption spectra for each dye, in its free and adsorbed forms, are discussed. Energy levels and electrochemical parameters are investigated to assess electron transfer efficiency between the excited dyes and the ZnTiO3 particles. Among the series, the dye TPA-3 shows superior behaviors, in terms of spontaneity of charge transfer with ZnTiO3 conduction band. The dye exhibits bidentate mode bonding with the semiconductor surface (1 0 1) as evidenced from its high adsorption energy. Such bonding enables stronger adherence between the dye and the semiconductor and enables more efficient charge transfer. The results encourage more theoretical and experimental study on TPA-3@ZnTiO3 DSSCs, with promising conversion efficiency and stability.

Performance, limits, and thermal stress analysis of high concentrator multijunction solar cell under passive cooling conditions

Concentration of solar radiation onto the surface of triple-junction solar cells causes high cell temperature and system failure. Recently, several cooling methods were proposed for these systems. However, quantitative evaluation of the essential heat transfer coefficients to maintain stable operation of these systems at different meteorological and operating conditions is not found in the literature. Therefore, in this study, a comprehensive three-dimensional coupled thermal and structural model is proposed for the latest triple-junction AZUR SPACE solar cell. The model is used to investigate the performance of an HCPV system under different solar concentration ratios (CRs), ambient temperature, direct solar irradiance, wind speed, backside heat transfer coefficient, and copper-II substrate area ratios. In addition, a new structure of the solar cell is proposed by modifying the typical solar cell assembly by changing the area of the rear copper layer. The results indicate that by increasing the ambient temperature, CR and direct solar irradiance significantly increase the predicted cell temperature at the same backside heat transfer coefficient. In addition, increasing copper-II substrate area ratios significantly reduces the average cell temperature at the same backside heat transfer coefficient and CR. At the highest backside heat transfer coefficient, when the copper-II substrate area increased, the cell temperature decreased to a certain limit and subsequently remained constant. Critical values of the highest backside heat transfer coefficient were about 200, 600, 1000, and 1600 W/m2 K at CRs of 50, 500, 1000, and 1500 Suns, respectively. In addition, at the highest backside heat transfer coefficient of 1600 W/m2 K, the critical area ratio values were about 2, 3, 4, and 6 at CRs of 50, 500, 1000, and 1500 Suns, respectively.

Influence of TiO2 layer on ultimate efficiencies for planar and nano-textured CH3NH3PbI3 solar cells

The influence of TiO2 layer on the ultimate efficiencies, η, i.e. efficiencies without considering carrier recombination, for the planar and nano-textured CH3NH3PbI3 (MAPbI3) perovskite solar cells (SCs) are investigated. In planar TiO2/MAPbI3 heterojunction SCs, in order to achieve the largest power conversion efficiency (PCE), the TiO2 layer thickness, d1, is important. With the finite difference time domain (FDTD) method, we demonstrated that when the MAPbI3 layer thickness, d2, is 250 nm, which is a common-most MAPbI3 layer thickness for perovskite SCs, η achieves maximum when d1 is 80 nm. Fabricating nano textures on SC surface is an important method to improve the PCE. We studied the effects of d1 and d2 on the optimized η, η0, for two kinds of nano-textured perovskite SCs: the SCs with the nontextured TiO2 layer and the column-shaped nano hollow (CLH) textured MAPbI3 layer, defined as the nontextured-TiO2/CLH-MAPbI3 SCs, and the SCs with CLH textured TiO2 and CLH textured MAPbI3 layers of the same hollow axes and radius, defined as the CLH-(TiO2/MAPbI3) SCs. Generally, when d1 and d2 are fixed, η0 for the CLH-(TiO2/MAPbI3) SC is larger than that for the nontextured-TiO2/CLH-MAPbI3 SC by ca. 5%.

Characterization of Core-Shell Spherical Lens for Microtracking Concentrator Photovoltaic System

The optical characteristics of a radially symmetrical core-shell spherical (CSSP) lens is analyzed for its suitability to application in microtracking concentrator photovoltaic systems (MTCPVs). The CSSP lens is compared to a conventional homogenous spherical lens through both ray-tracing simulations and outdoor experiments. Simulation results show that the CSSP lens is superior to the conventional homogenous spherical lens in terms of its optical efficiency for long focal lengths, for which the CSSP lens exhibits less spherical and chromatic aberrations. Outdoor experiments are conducted using test concentrator photovoltaic (CPV) modules with prototype CSSP and homogenous spherical lenses; the trend of the measured short circuit current agrees with the that of the simulated optical efficiency for both lenses. Furthermore, compared to the homogenous lens, the CSSP lens significantly increases module efficiency because of its better illumination uniformity at the solar cell surface. The optical characteristics of the CSSP lens are preferable for MTCPVs with a spherical lens array to achieve a higher module efficiency for a wider incidence angle although further studies on more practical system configurations are needed.

SiN/SiO2 passivation stack of n-type silicon surface

Abstract The SiN/SiO2 stack is widely used to passivate the surface of n-type monocrystalline silicon solar cells. In this work, we have undertaken a study to compare the stack layer obtained with SiO2 grown by both rapid thermal and chemical ways to passivate n-type monocrystalline silicon surface. By varying the plateau time and the plateau temperature of the rapid thermal oxidation, we determined the parameters to grow 10 nm thick oxide. Two-step nitric acid oxidation was used to grow 2 nm thick silicon oxide. Silicon nitride films with three refractive indices were used to produce the SiN/SiO2 stack. Regarding this parameter, the minority carrier lifetime measured by means of QSSPC revealed that the refractive index of 1.9 ensured the best passivation quality of silicon wafer surface. We also found that stacks with nitric acid oxidation showed definitely the best passivation quality. In addition to produce the most efficient passivation, this technique has the lowest thermal budget.

The n-type Si-based materials applied on the front surface of IBC-SHJ solar cells**Project supported by the National Key Research Program of China (Grant Nos. 2018YFB1500500 and 2018YFB1500200), the National Natural Science Foundation of China (Grant Nos. 51602340, 51702355, and 61674167), and JKW Project, China (Grant No. 31512060106).

Interdigitated back contact silicon hetero-junction (IBC-SHJ) solar cells exhibit excellent performance owing to the IBC and SHJ structures. The front surface field (FSF) layer composed of electric field passivation and chemical passivation has been proved to play an important role in IBC-SHJ solar cells. The electric field passivated layer n+-a-Si: H, an n-type Si alloy with carbon or oxygen in amorphous phase, is simulated in this study to investigate its effect on IBC-SHJ. It is indicated that the n+-a-Si: H layer with wider band gap can reduce the light absorption on the front side efficaciously, which hinders the surface recombination of photo-generated carriers and thus contributes to the improvement of the short circuit current density Jsc. The highly doped n+-a-Si: H can result in the remakable energy band bending, which makes it outstanding in the field passivation, while it makes little contribution to the chemical passivation. It is noteworthy that when the electric field intensity exceeds 1.3 × 105 V/cm, the efficiency decrease caused by the inferior chemical passivation is only 0.16%. In this study, the IBC-SHJ solar cell with a front n+-a-Si: H field passivation layer is simulated, which shows the high efficiency of 26% in spite of the inferior chemical passivation on the front surface.

Opto-electronic properties of stable blue photosensitisers on a TiO2 anatase-101 surface for efficient dye-sensitised solar cells

We study the electronic and optical properties of narrow energy gap blue dyes, R6, featuring a stronger electron-donating poly-aromatic hydrocarbon, 9,19-dihydrobenzo[1′,10′]phenanthro[3′,4′:4,5]thieno[3,2-b]-benzo[1,10]phenanthro[3,4-d]thiophene (BPT2), and R4, featuring 4H’,4′H-2,2′-bibenzo[1.10]phenanthro[4,3-b]thiophene (2BPT). BPT2 and 2BPT are tethered with an auxiliary diarylamine electron donor and an electron acceptor of 4-(7-ethynylbenzo[c][1,2,4]thiadiazol-4-yl)benzoic acid, respectively. We explore these dyes with varying acceptor moieties, along with their binding interaction, at a TiO2 anatase-101 surface. All isolated dye molecules absorbed light in 1.97–2.14 eV range, although their binding-to-anatase affinities were very similar; for all absorbed dyes, valance-band maxima and the conduction-band minima of the composites system are mainly localized on dye and the TiO2-slab, respectively.

Increased Absorption with Al Nanoparticle at Front Surface of Thin Film Silicon Solar Cell

This article presents an effective structural design arrangement for light trapping in the front surface of a thin film silicon solar cell (TFSC). Front surface light trapping rate is significantly enhanced here by incorporating the Aluminium (Al) nanoparticle arrays into silicon nitride anti-reflection layer. The light trapping capability of these arrays is extensively analyzed via Finite Difference Time Domain (FDTD) method considering the wavelength ranging from 400 to 1100 nm. The outcome indicates that the structural parameters associated with the aluminium nanoparticle arrays like particle radii and separations between adjacent particles, play vital roles in designing the solar cell to achieve better light trapping efficiency. A detailed comparative analysis has justified the effectiveness of this approach while contrasting the results found with commonly used silver nanoparticle arrays at the front surface of the cell. Because of the surface plasmon excitation, lower light reflectance, and significant near field enhancement, aluminium nanoparticle arrays offer broadband light absorption by the cell.

Sensitization of silicon by singlet exciton fission in tetracene.

Silicon dominates contemporary solar cell technologies1. But when absorbing photons, silicon (like other semiconductors) wastes energy in excess of its bandgap2. Reducing these thermalization losses and enabling better sensitivity to light is possible by sensitizing the silicon solar cell using singlet exciton fission, in which two excited states with triplet spin character (triplet excitons) are generated from a photoexcited state of higher energy with singlet spin character (a singlet exciton)3-5. Singlet exciton fission in the molecular semiconductor tetracene is known to generate triplet excitons that are energetically matched to the silicon bandgap6-8. When the triplet excitons are transferred to silicon they create additional electron-hole pairs, promising to increase cell efficiencies from the single-junction limit of 29 per cent to as high as 35 per cent9. Here we reduce the thickness of the protective hafnium oxynitride layer at the surface of a silicon solar cell to just eight angstroms, using electric-field-effect passivation to enable the efficient energy transfer of the triplet excitons formed in the tetracene. The maximumcombined yield of the fission in tetracene and the energy transfer to silicon is around 133 per cent, establishing the potential of singlet exciton fission to increase theefficiencies of silicon solar cells and reduce the cost of the energy thatthey generate.

Control of the distance between porphyrin sensitizers and the TiO2 surface in solar cells by designed anchoring groups

Unsymmetrical porphyrins were rationally-designed and synthesized to investigate the relation between their structure, properties and adsorption geometries, and their relative performance as dyes in dye-sensitized solar cells. Photophysics, electrochemical and TiO2 anchoring properties of the new unsymmetrical N-glycolic acid amino phenyl porphyrins were evaluated. Most dyes showed good energy matching between excited state energies and the TiO2 conduction band. Depending on the porphyrins, anchoring to TiO2 occurred with only one carboxyl anchor group or with two N-glycolic acid amino phenyl connected to opposite and adjacent phenyl groups. It was found that cell efficiencies normalized for surface coverage are strongly affected by the adsorption geometry and spacer linker flexibility. The effective distance between the porphyrin core and the TiO2 surface has key importance in cell efficiencies. The data is consistent with a through-space electron transfer and anchoring viaN-glycolic acid substituents located in adjacent phenyl groups results in higher surface coverage normalized cell efficiencies.

Enhancement of Sb2Se3 thin-film solar cell photoelectric properties by addition of interlayer CeO2

Antimony selenide (Sb2Se3) thin films are light-absorbing materials used for low-cost, highly efficient thin-film solar cells. However, because it is deposited onto a comparatively rough substrate, stacking growth of a Sb2Se3 thin film negatively impacts formation of the heterojunction. For this study, Sb2Se3 thin-film solar cells were fabricated in a FTO/CdS/CeO2/Sb2Se3/Au configuration. An ultrathin layer of cerium dioxide (CeO2) was deposited onto the CdS surface by evaporation, and the thickness of the CeO2 interlayer was optimized to improve the photoelectric properties of the solar cells. Compared to the CdS surface in conventional Sb2Se3 thin-film solar cells (FTO/CdS/Sb2Se3/Au), the surface of the CdS buffer in our solar cells was smoothed by the CeO2 layer, which induced columnar growth of the Sb2Se3 grains. Furthermore, diffusion of Ce4+ into Sb2Se3 enhanced its crystallinity and improved the evenness of the Sb2Se3 thin-film surface. The photo-conversion efficiency (PCE) of a solar cell with a 2-nm thick CeO2 interlayer reached 5.14%.

Effect of Imbalanced Charge Transport on the Interplay of Surface and Bulk Recombination in Organic Solar Cells

Surface recombination has a major impact on the open-circuit voltage ($V_\text{oc}$) of organic photovoltaics. Here, we study how this loss mechanism is influenced by imbalanced charge transport in the photoactive layer. As a model system, we use organic solar cells with a two orders of magnitude higher electron than hole mobility. We find that small variations in the work function of the anode have a strong effect on the light intensity dependence of $V_\text{oc}$. Transient measurements and drift-diffusion simulations reveal that this is due to a change in the surface recombination rather than the bulk recombination. We use our numerical model to generalize these findings and determine under which circumstances the effect of contacts is stronger or weaker compared to the idealized case of balanced charge transport. Finally, we derive analytical expressions for $V_\text{oc}$ in the case that a pile-up of space charge is present due to highly imbalanced mobilities.

Vanadium Oxide as Transparent Carrier-Selective Layer in Silicon Hybrid Solar Cells Promoting Photovoltaic Performances

Vanadium pentoxide (V2O5) has been proposed as a promising selective contact for holes in organic electronic devices. In this study, the strategy was undertaken for minimizing the possible charge recombination at electrode surfaces in the silicon-based hybrid solar cells and further allowed the exceptional capability for hole extraction. This was accomplished by inserting the mixed vanadium oxide (VOx) phases based on a simplified low-temperature fabrication process. Detailed examinations of crystallinity, chemical states and compositions, topography, and optical transmittance of such VOx layer were performed, revealing the coexistence of V2O3 and V2O5 phases that facilitated the hole-selective contact due to establishing the ohmic-like interfaces as well as blocking the transport of electrons, and the optimal anneal treatment at 200 °C was further validated. On the basis of this, the insertion of a VOx electron-blocking layer in the integrated organic/inorganic hybrid solar cells was fully fabricated with solution processing methods, presenting the leading conversion efficiency of 14.4% being approximately 1.6 times superior than the conventional VOx-free hybrid solar cells. These results provided a viable rule toward realizing the high-performance and low-cost solar cells and might further offer the high potential for other functional applications based on hybrid material designs.

Using phosphor to enhance the efficiency of commercial solar cells

The non-rare-earth phosphor Ca2ZnMoO6 has a luminescence of 375–655 nm and emits near-white light. This study investigated it as a down-shifting layer to improve the efficiency of commercial flexible solar cells. The first structure was a solar cell/thick-film Ca2ZnMoO6 phosphor layer (TLDU device); a controlled light source was shone on the top, and UV light was shone on the bottom. The second structure was a solar cell/thick-film Ca2ZnMoO6 phosphor layer with an Al reflective layer (TLDR device), and only a controlled light source was used. We compared the power output efficiencies of the two structures with the efficiency of a control device. When the [Formula: see text]–[Formula: see text] properties of the three different devices were measured, the [Formula: see text] value underwent no apparent change, but the [Formula: see text] increased in the TLDU and TLDR devices. These results suggest that if placed on the bottom surface of commercial solar cells, Ca2ZnMoO6 phosphor could improve their efficiency.

Improved photovoltaic performance of monocrystalline silicon solar cell through luminescent down‐converting Gd2O2S:Tb3+ phosphor

AbstractThis work reports on efforts to enhance the photovoltaic performance of standard p‐type monocrystalline silicon solar cell (mono‐Si) through the application of ultraviolet spectral down‐converting phosphors. Terbium‐doped gadolinium oxysulfide phosphor and undoped‐gadolinium oxysulfide precursor powders were prepared by a controlled hydrothermal decomposition of a urea homogeneous precipitation method. The resulting rare‐earth element hydroxycarbonate precursor powders were then converted to the oxysulfide by annealing at 900°C in a sulfur atmosphere. The as‐prepared phosphors were encapsulated in ethylene vinyl acetate co‐polymer resin and applied on the textured surface of solar cell using rotary screen printing. Comparative results from X‐ray powder diffraction, field emission scanning electron microscopy, scanning transmission electron microscopy, and photoluminescence spectroscopy studies on the microstructure and luminescent properties of the materials are reported. We also compared the optical reflectance and external quantum efficiency response of the cells with and without a luminescent phosphor layer. The results obtained on the terbium‐doped gadolinium oxysulfide phosphor show clearly that the down‐conversion effect induced by the terbium dopant play a crucial role in enhancing the photovoltaic cells' performance. Under an empirical one‐sun illumination, the modified cells showed an optimum enhancement of 3.6% (from 16.43% to 17.02%) in conversion efficiency relative to bare cells. In the concentration range of 1 to 2.5 mg/mL, EVA/Gd2O2S (blank) composites also improve electrical efficiency, but not as much as EVA/Gd2O2S:Tb3+ composites.

Thermomechanical stress in solar cells: Contact pad modeling and reliability analysis

This study analyses thermomechanical stresses in silicon solar cells after the soldering process by finite element modeling. An experimentally validated model shows compressive and tensile stresses, longitudinal and transversal to a busbar or a pad row on the surface of a silicon solar cell. The impact of the interconnector segments at and in between two solder pads was investigated and characteristic locations of maximum stress were identified. In addition, the influence of the layout of the contact metallization on the thermomechanical stress was identified by geometry variations to reveal design guidelines that lead to reduced thermomechanical stress in a solar cell after the soldering process. The model results reveal maxima of the tensile stress located at the outermost contacts. Furthermore, a significant influence of the distance between the outermost contact areas and the solar cell edge was determined; with decreasing distance, the compressive stress maxima are higher, but in contrast the more critical tensile stress maxima decrease. For connected pad rows tensile stress maxima are larger compared to single pad connection, which shows the influence of the interconnector segments in between the solder joints of a pad row. After several stages of thermal cycling, electroluminescence measurements showed, in compliance with the model results, contact damages, mainly at the outermost contacts. Furthermore, connected pad rows revealed a steadily growing amount of damaged contacts, whereas single solder joints showed no defects up to 400 thermal cycles.

OPTIMIZATION OF POROUS SILICON CHARACTERISTICS FOR SOLAR BATTERIES

The aim is to form the anti-reflective layers of porous silicon on the solar cell surface in the presence of the current-collecting contact comb at the effective area, as well as the study of the state of front contact system of solar cells after etching on their main characteristics.The analysis of the influence of electrochemical etching on the state of the solar cell front contact system without antireflection coating was carried out on the basis of the dependences of the reflectance spectrum of porous silicon on its thickness and refractive index. In the range of wavelengths of 550-850 nm, a minimal reflection from the porous layer surface for the thickness of porous silicon from 70 to 100 nm was found, and its refractive index ranges from 1.35 to 1.9.The critical time of staying of the solar cell structure in the electrolyte, the excess of which leads to the damage of contact fingers of the front current-collecting contact comb was found. For anodization in an electrolyte C2 H5 OH:HF=1:1, the critical time was 45 s. The reduction of the anodizing time to 10 s at anodic charge density of 0.46 C/cm2 allowed to obtain porous silicon layers without significant damage to the current-collecting comb. By reducing the duration of electrochemical treatment to 3-6 s and increasing the anode current, it was possible to completely prevent the damage of the contact system.The results of study of the main solar cell parameters before and after formation of anti-reflective layer on the basis of porous silicon showed that for mono- and multicrystalline solar cells the increase in photocurrent exceeded 50%, the efficiency increased by 25% and 22% respectively for mono- and multicrystalline samples. At the same time, for all tested samples, the open-circuit voltage decreased by 2.5%, and the fill factor degraded by 10.7% and 18.8% for mono- and multicrystalline solar cells, respectively.