Solar Cell Configuration Research Articles

Coral-like perovskite nanostructures for enhanced light-harvesting and accelerated charge extraction in perovskite solar cells

A novel coral-like perovskite nanostructured layer was grown on a compact perovskite foundation layer by the facile surface modification with dimethylformamide/isopropanol (DMF/IPA) as co-solvent. Surface morphological characterizations with SEM and XRD analyses revealed a growing mechanism of the new morphology, which was composed of the perovskite decomposition and recrystallization, excessive-PbI2 extraction, and sequential formation of coral-like nanostructured perovskite layer. The coral-like perovskite nanostructures resulted in significant light scattering, enhancing the light-harvesting efficiency, and thus augmenting the photocurrent density. Moreover, the geometric configuration of the perovksite solar cells was changed from planar to bulk heterojunction, which results in the acceleration of charge separation and extraction due to the high surface area at the interface between the obtained perovskite and hole-transport layers. The optimal perovskite solar cell exhibited an impressive power conversion efficiency (PCE) of 19.47%, as compared to that of the pristine cell (17.19%).

Efficient light harvesting in hybrid quantum dot-interdigitated back contact solar cells via resonant energy transfer and luminescent downshifting.

In this paper, we propose a hybrid quantum dot (QD)/solar cell configuration to improve performance of interdigitated back contact (IBC) silicon solar cells, resulting in 39.5% relative boost in the short-circuit current (JSC) through efficient utilisation of resonant energy transfer (RET) and luminescent downshifting (LDS). A uniform layer of CdSe1-xSx/ZnS quantum dots is deposited onto the AlOx surface passivation layer of the IBC solar cell. QD hybridization is found to cause a broadband improvement in the solar cell external quantum efficiency. Enhancement over the QD absorption wavelength range is shown to result from LDS. This is confirmed by significant boosts in the solar cell internal quantum efficiency (IQE) due to the presence of QDs. Enhancement over the red and near-infrared spectral range is shown to result from the anti-reflection properties of the QD layer coating. A study on the effect of QD layer thickness on solar cell performance was performed and an optimised QD layer thickness was determined. Time-resolved photoluminescence (TRPL) spectroscopy was used to investigate the photoluminescence dynamics of the QD layer as a function of AlOx spacer layer thickness. RET can be evoked between the QD and Si layers for very thin AlOx spacer layers, with RET efficiencies of up to 15%. In the conventional LDS architecture, down-converters are deposited on the surface of an optimised anti-reflection layer, providing relatively narrowband enhancement, whereas the QDs in our hybrid architecture provide optical enhancement over the broadband wavelength range, by simultaneously utilising LDS, RET-mediated carrier injection, and antireflection effects, resulting in up to 40% improvement in the power conversion efficiency (PCE). Low-cost synthesis of QDs and simple device integration provide a cost-effective solution for boosting solar cell performance.

TCAD 2D numerical simulations for increasing efficiency of AlGaAs – GaAs Solar Cells

The performance of solar cells has improved quickly in recent years, the latest research focuses on thin cells, multijunction cells, solar cells of the group III-V compounds, Tandem cells, etc. In the present work, numerical simulations are developed, using SENTAURUS TCAD as a tool, in order to obtain a solar cell model based on Galium Arsenide (GaAs). This solar cell corresponds to the so-called "Thin Films" due to the fact that can make layers thinner than we would have if we work with conventional semiconductors, such as; Silicon or Germanium; thus opening the possibility of placing the cell as a top layer within a tandem solar cell configuration with compounds of group III-V. That is why two types of simulations are performed with respect to the contact of the rear contact; one corresponds to the cell with a lower contact equal to the length of the cell and the other with a small contact of 5 μm. In addition, the cell undergoes an optimization process by modifying the geometry and doping of the layers that comprise it, in order to improve its performance. To achieve this objective, the initial conditions and the appropriate simulation parameters must be determined, which have been selected and corroborated with the literature, allowing us to arrive at coherent results and optimal models of solar cell design through numerical simulations.

Field stitching approach for the wave optical modeling of black silicon structures.

The interest in black silicon structures as an anti-reflective interface at the front side of silicon solar cells increased strongly with the rise of diamond wire sawing. The application of optical modeling in order to predict optimal structure parameters could be highly valuable. However, due to the random nature of the structure as well as dimensions in the range of the wavelengths of interest, optical modeling is still a challenge. Within this work, the stitching method of rigorously calculated fields is extended and applied to a black silicon structure. A Fourier transform is used to determine the angular intensity distribution in the far field. In combination with the OPTOS formalism, this allows modeling of silicon substrates with black silicon front side and shows a reasonably good agreement with optical measurement results. Implementing the investigated structure into a solar cell configuration reveals not only a low reflectance but also a very good light trapping performance close to that of a Lambertian scatterer.

All-Nanoparticle SnO2/TiO2 Electron-Transporting Layers Processed at Low Temperature for Efficient Thin-Film Perovskite Solar Cells

Solution-processed metal halide perovskite materials have revealed outstanding optoelectronic features that make them uniquely suited for photovoltaic applications. Although a rapid progress has led to performances similar to inorganic thin film technologies, the fabrication method of some of the most widely used electron selective layers, based on either mesoporous architectures or high annealing temperatures, may limit yet a future large-scale production. In that regard, planar perovskite solar cell configurations that can be processed at low temperatures are more desirable. Herein, we demonstrate that a few tens of nanometers thick bilayer, made of two types of inorganic oxide nanoparticles, can perform as a robust and low-temperature-processed electron-selective contact for planar perovskite solar cells. Aside from boosting the average efficiency of planar opaque devices, the proposed method allowed us to preserve the main photovoltaic characteristics when thinner active layers, usually exhibiting a n...

A Facile Preparative Route of Nanoscale Perovskites over Mesoporous Metal Oxide Films and Their Applications to Photosensitizers and Light Emitters

AbstractBy two‐step sequential Pb2+ adsorption and reaction with methylammonium‐iodide (MAI) or ‐bromide (MABr) at a low concentration level of 0.06–0.10 m over mesoporous TiO2 or ZrO2 film, a well‐defined nanoscale CH3NH3PbI3 (MAPbI3) photosensitizer or CH3NH3PbBr3 (MAPbBr3) light emitter could be prepared in situ, respectively in a reproducible and atom‐economical way. The as‐prepared nanoscale perovskites are compared with their thin film counterparts in terms of light absorption/emission, crystallinity, surface morphology, and energy‐conversion efficiency. The nanoscale perovskite‐decorated films display more transparency than the bulky film due to the much lower amount deposited, while blueshifted and overwhelmingly brighter photoluminescence is observed in the “nano” relative to the “bulk” due to quantum size confinement. Transmission electron microscopy images also clearly show that a few nanometer‐sized perovskite dots are deposited homogeneously over the surface of TiO2‐ or ZrO2‐particulate film in the course of the current preparative route. When the nano‐MAPbI3 is tested as a photosensitizer in a solid‐state dye‐sensitized solar cell configuration with a very thin (≈650 nm) TiO2 mesoporous film, it has a promising initial power conversion efficiency of 6.23%, which outperformed the result of 2.28% from a typical organic molecular dye coded as MK‐2.

Importance of CdS buffer layer thickness on Cu2ZnSnS4-based solar cell efficiency

Cu2ZnSnS4 (CZTS) thin films were grown on Mo-coated soda lime glass (SLG) substrates by the sulfurization of DC magnetron-sputtered Zn, Sn and Cu metallic precursors under a sulfur atmosphere at 550 °C for 45 min. Understanding the composition and structure of the CZTS absorber layer is necessary to obtain efficient solar cells. With this aim, x-ray diffractometry, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy were used to investigate the CZTS absorber layers. CZTS absorber films were obtained and found to be Cu-poor and Zn-rich in composition, which are both qualities desired for efficient solar cells. CdS was used as a buffer layer and was grown by the chemical bath deposition technique. The optical properties of CdS films on SLG were searched for using a spectroscopic ellipsometer and the results revealed that the bandgap increases with film thickness increment. CZTS-based solar cells with different CdS buffer layer thicknesses were prepared using a SLG/Mo/CZTS/CdS/ZnO/AZO solar cell configuration. The influence of the CdS buffer layer thickness on the performance of the CZTS solar cells was investigated. Device analysis showed that electrical characteristics of solar cells strongly depend on the buffer layer’s thickness. Highly pronounced changes in VOC, fill factor and JSC parameters, which are the main efficiency limiting factors, with changing buffer layer thicknesses were observed. Our experiments confirmed that decreasing the CdS thickness improved the efficiency of CZTS solar cells down to the lowest thickness limit.

Nanocrystalline Pyrite for Photovoltaic Applications

AbstractTransition metal sulfides (TMSs) are of special interest in energy conversion and storage devices. Amongst all sulfides, fool's gold or iron pyrite (FeS2) is potentially an attractive candidate for photovoltaic applications. Iron pyrite has risen to prominence due to its distinct properties and abundance in nature to meet the large scale needs. It is considered as environmentally benign solar absorber material with high absorption coefficient, α > 6 x105 cm−1 for λ ≥ 700 nm and suitable energy bandgap (Eg=0.95 eV). Numerous physical and chemical methods have been employed to deposit nanocrystalline pyrite thin films directly from source materials or indirectly by sulfuration. This review gives an overview of pyrite as a low cost photovoltaic absorber material for contemporary solar cell structures. In addition, practical approaches like the rational design of nanocomposites, band gap engineering and nanostructure synthesis of pyrite for improving its properties particularly photovoltaic properties are also deliberated. Moreover, limitations, challenges, remedies and prospects of pyrite as potential photovoltaic material are also reviewed to further advance the development of pyrite‐based solar cell configurations.

Increased performance of thin-film GaAs solar cells by rear contact/mirror patterning

Current thin-film GaAs solar cells typically have a completely metal covered rear side that functions as back contact, rear mirror and stable carrier to the solar cell. However, the bottom contact layer, that typically remains whole in this configuration, absorbs a large amount of photons that would otherwise be reflected back into the cell structure. This work identifies and quantifies the performance limits by non-optimal rear contact reflectance in the standard configuration of thin-film GaAs solar cells and proposes a design solution. In this study we show that the total reflectance at the back of the solar cell is increased from 63.5% to 93.2% by partially etching the absorbing GaAs contact layer and applying a dielectric material in the etched regions. Both shallow junction and deep junction cells were produced, and for deep junction solar cells the patterning resulted in a more than linear increase in the open circuit voltage and a linear increase in the short circuit current, which is in good agreement with previously reported numerical models.

Diminished band discontinuity at the p/i interface of narrow-gap a-SiGe:H solar cell by hydrogenated amorphous silicon oxide buffer layer

We optimized hydrogenated amorphous silicon oxide (a-SiOx:H) as a buffer layer at the p/i interface of hydrogenated amorphous silicon germanium (a-SiGe:H) solar cells. This buffer layer was intended to effectively diminish the band discontinuity between the high-bandgap p-window layer and low-gap a-SiGe:H absorption layer, thereby enhancing the cell performance. The open-circuit voltage (Voc) increased by 3.7% as the [CO2]/[SiH4] gas ratio increased from 0 to 0.06. In addition, the short-circuit current density (Jsc) gradually increased with the gas ratio. Using the optimized a-SiOx:H buffer layer, a high performance of 9.6% was recorded for narrow-gap a-SiGe:H thin film solar cells. a-SiGe:H solar cells with optimized a-SiOx:H buffer layers, used as middle subcells, are expected to enhance the total Voc of triple-junction configuration solar cells.

All spray pyrolysis-coated CdTe\u2013TiO2 heterogeneous films for photo-electrochemical solar cells

Cadmium telluride (CdTe) thin films of different thicknesses deposited onto titanium dioxide (TiO2) nanoparticle layer by spray pyrolysis deposition (SPD) are demonstrated as major photo-active semiconductor in photo-electrochemical solar cell configuration using iodide/triiodide (I−/I3−) redox couple as a hole transport layer. The CdTe–TiO2 heterogeneous films were characterized by X-ray photoelectron spectroscopy which identified doublet split of Cd 3d and Ti 2p which confirms CdTe and TiO2. Optical absorbance and transmittance of CdTe and TiO2 films which were examined by UV–Vis spectroscopy confirm that the optical bandgap of CdTe is 1.5 eV with a dominant photo-absorption in the spectral window of 350–800 nm, while TiO2 showed a bandgap of 3.1 eV and is optically transparent in the visible spectral window. The present work examined photo-anodes comprising 1, 3, 5, and 10 SPD cycles of CdTe coated on TiO2 nanoparticle layer. The solar cell with 5 SPD cycles of CdTe resulting in 0.4% efficiency. Results can be articulated to the CdTe deposited by 5 SPD cycles provided an optimum surface coverage in the bulk of TiO2, while the higher SPD cycles leads to agglomeration which blocks the porosity of the heterogeneous films.

Highly phase-pure spray-pyrolysed Cu2SnS3 thin films prepared by hybrid thermal treatment for photovoltaic applications

The structure and physical properties of thin films of ternary photovoltaic absorber Cu2SnS3 on soda-lime glass substrate deposited by cost effective spray pyrolysis following a hybrid thermal annealing (HTA) have been investigated. The advantage of HTA-sulfurization over standard thermal annealing (STA) and rapid thermal annealing (RTA) is established for Cu2SnS3 (CTS). The X-Ray diffraction (XRD) and Raman spectroscopy reveals highly phase pure Cu2SnS3 is produced through effective relaxation of compressive stress and increased crystallinity by the HTA-sulfurization step. Additionally, scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDX) reveals that the evolution of secondary phases, CuxSy (x, y: 116, 64; 2, 1; 1.8, 1; 51, 27; 6, 6 etc) could be effectively prevented by the HTA process over the STA and RTA. The optimized HTA-CTS thin films obtained are of p-type conductivity with the carrier concentration, resistivity and mobility of 5.5 × 1020 cm−3, 9.8 × 10−3Ω-cm and 1.15 cm2V−1s−1, respectively. The optical band gap of about 1.65 eV with large absorption coefficient of 105 cm−1 demonstrates it as an ideal candidate for thin film solar cells. A solar cell configuration of glass/F:SnO2/CTS/CdS/ZnO:Al/Al shows an open circuit voltage of 225 mV.

Non-toxic configuration of indium selenide nanoparticles- Cu2ZnSnS2Se2 /carbon fabric in a quasi solid-state solar cell

Non-toxic indium selenide (In2Se3) semiconducting nanoparticles as photosensitizers and an alloyed copper-zinc-tin-sulfide-selenide (Cu2ZnSnS2Se2) coated carbon-fabric as counter electrode are assembled into a solar cell configuration for the first time. In2Se3 nanoparticles with a band gap of 1.78 eV, harvest blue-green photons as well as some portion of the red region of the solar spectrum and they exhibit a broad emission in the visible region, and the emissions via absorption of high energy- and low energy-photons show short and long excited electron lifetimes respectively. A polymeric electrolyte with poly(hydroxyethyl methacrylate) as the gelatinizing agent is employed as the hole transport layer in solar cells. Cu2ZnSnS2Se2/carbon-fabric is more efficient than carbon-fabric as a counter electrode, for the solar cell based on the former shows a lower electron transport resistance, a higher recombination resistance at the photoanode/gel interface, and an increased chemical capacitance for the photoanode, cumulatively resulting in rapid electron injection to the electrolyte at the cathode. The champion solar cell with TiO2/In2Se3-S2-/poly(hydroxyethyl methacrylate) gel-Cu2ZnSnS2Se2/carbon-fabric architecture delivers a power conversion efficiency of 4.15%, thus demonstrating that quasi solid-state quantum dot solar cells with non-toxic components can be easily fabricated and even scaled up for real time applications.

Rietveld refinement of crystal structure of perovskite CH3NH3Pb(Sb)I3 solar cells

The crystal structures of perovskite CH3NH3Pb1−xSbxI3 (x = 0 and 0.15) films in the solar cell configuration were studied by using Rietveld refinement. Optimizing atomic positions and site occupancies, satisfactory agreement was obtained between measured and calculated X-ray diffraction profiles. The refined composition ratio of metal, methylammonium (MA), and halogen was for the Sb-free solar cell. For the antimonized solar cell, this ratio was . The decreased MA occupancy in the antimonized solar cell was considered as a result of the compensation effect of the increased positive charge brought about by replacing Pb2+ with Sb3+.

20 renewable biowastes derived carbon materials as green counter electrodes for dye-sensitized solar cells

Twenty types of biowastes derived carbon materials (BCM) synthesized by a facile one-step pyrolysis were developed as counter electrodes for the configuration of dye-sensitized solar cells (DSSCs). The biowastes selected for the BCM preparation were divided into three groups: (i) eleven woods, including weeping willow, phoenix, camphor, Chinese fir, maple, peach, poplar, cypress, tea-oil camellia, orange, and chinaberry; (ii) seven leaves, including pine needles, camphor, palm, maple, poplar, Chinese fir, and red after-wood; and (iii) two papers, namely filter paper and facial tissue. Each of the BCM based DSSCs shows a higher efficiency than the graphite based counterparts. The efficiencies of the DSSCs employing the BCM prepared from woods and leaves vary in a range 1.23% -1.91% and 1.07%-1.85%, respectively, while that of the devices using the graphite is 0.77%. The peak efficiency in both groups of the wood and leaf based cells is achieved by employing the phoenix wood and the palm leaf as the raw materials, respectively. Compared with the porous BCM obtained from the woods and leaves, the fibrous BCM fabricated from the papers show better efficiencies of around 4.70% for use in the DSSCs. The high efficiency is mainly attributed to the superior catalytic activity and faster electron transportation for tri-iodide (I3−) reduction induced by the unique morphological and structural characteristics of the paper derived BCM, such as hierarchical fibrous carbon skeletons at nanometer and micron scales, abundant exposed microcrystal edges and defects, rough surface at nanoscale with rich burrs and convex microstructures, and oxygen-containing surface functional groups. Furthermore, the efficiency of the DSSCs employing the paper derived BCM is equal to about 88% of that of the devices using the mesoporous carbon synthesized from the phenolic resin mixtures based on polymerization-induced phase separation.

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

Al is a commonly used material for rear side metallization in commercial silicon (Si) wafer solar cells. In this study, through‐the‐silicon spectroscopic ellipsometry is used in a test sample to measure Al+Si interface optical properties like those in Si wafer solar cells. Two different spectroscopic ellipsometers are used for measurement of Al+Si interface optical properties over the 1128–2500 nm wavelength range. For validation, the measured interface optical properties are used in a ray tracing simulation over the 300–2500 nm wavelength range for an encapsulated Si solar cell having random pyramidal texture. The ray tracing model matches well with the measured total reflectance at normal incidence of a commercially available Si module. The Al+Si optical properties presented here enable quantitative assessment of major irradiance/current flux losses arising from reflection and parasitic absorption in encapsulated Si solar cells.

Towards an optimum silicon heterojunction solar cell configuration for high temperature and high light intensity environment

We report on the performance of Silicon Heterojunction (SHJ) solar cell under high operating temperature and varying irradiance conditions typical to desert environment. In order to define the best solar cell configuration that resist high operating temperature conditions, two different intrinsic passivation layers were tested, namely, an intrinsic amorphous silicon a-SiOx:H with CO2/SiH4 ratio of 0.4 and a-SiOx:H with CO2/SiH4 ratio of 0.8, and the obtained performance were compared with those of a standard SHJ cell configuration having a-Si:H passivation layer. Our results showed how the short circuit current density Jsc, and fill factor FF temperature-dependency are impacted by the cell’s configuration. While the short circuit current density Jsc for cells with a-SiOx:H layers was found to improve as compared with that of standard a-Si:H layer, introducing the intrinsic amorphous silicon oxide (a-SiOx:H) layer with CO2/SiH4 ratio of 0.8 has resulted in a reduction of the FF at room temperature due to hindering the carrier transport by the band structure. Besides, this FF was found to improve as the temperature increases from 15 to 45 °C, thus, a positive FF temperature coefficient.

Simulations of Non-Monolithic Tandem Solar Cell Configurations for Electrolytic Fuel Generation

The efficient conversion of solar energy to fuels through electrochemical processes requires optimizing the photovoltage and current for an ideal coupling with the electrolysis reaction. A modular architecture for tandem photovoltaics is explored and modeled as a strategy to drive an arbitrary electrolysis reaction from sunlight to produce the maximum fuel product in a day. Non-monolithic tandem solar cells based on Si and organometal halide perovskites are simulated in two-terminal and four-terminal arrangements and coupled with experimental data on water-splitting and CO2 reduction to predict the performance of an integrated solar fuels system. An appropriately designed four-terminal system is modeled to match or exceed the output of a two-terminal system. The four-terminal configuration leads to a 15.8% increase in daily H2 production with a 1.5 eV/1.12 eV system, and a 5.3% increase with a more ideal 1.74 eV/1.12 eV combination. The four-terminal system is also simulated to match the production of formic acid and increase the production of ethylene by 20.4% in a Cu-catalyzed CO2 reduction process compared to a two-terminal tandem arrangement. The effects of series resistance in non-monolithic tandem devices are modeled as well, showing a much greater tolerance to cell width in the four-terminal systems.

Performance of silicon solar cells under filtered spectra and different light intensities

Solar cells operate under various light intensities. In addition, in a tandem solar cell configuration, the bottom cell receives a spectrum that is filtered by the top cell. The performance of the bottom cell at low light intensity is thus of great importance. In this paper, we study various types of silicon solar cells under various light intensities and filtered spectra. We find that, as expected, the short-circuit current varies linearly with the illumination intensity, regardless of the input spectrum. However, we also observe that for a constant number of incident photons but different long-pass filters (i.e., different photogeneration profiles), the short-circuit current density of the solar cells reduces with increasing cut-on wavelength of the used filter. According to our analysis, the loss in short-circuit current can be partly explained by the strong wavelength dependence of the external quantum efficiency at long wavelengths (1050–1200 nm) as well as the different carrier generation profiles under filtered spectra.

Morphology-controlled synthesis and characterization of CdTe micro-/nanoscale structures by electrodeposition method

Cadmium telluride (CdTe) micro-/nanoscale structures, including micropillars, micro-/nanorods and microflowers arrays, were successfully and controllably synthesized by electrodeposition on nickel substrates. Various characterization techniques, such as X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectroscopy, selected area electron diffraction and Raman spectroscopy, were used to characterize the structures and properties of the as-prepared films. The structural analysis revealed that the as-synthesized CdTe films deposited in different concentrations of sulfuric acid system had cubic phases and possessed a polycrystalline structure with preferred orientations along the [111] direction. The results of SEM showed that the sulfuric acid concentrations had a significant effect on the morphology evolution from micropillar arrays to microflower arrays, and a possible formation mechanism was proposed. In addition, according to the results of the optical and photoelectrochemical performances in the visible-light region, the as-synthesized films have considerable potential to be applied as absorber materials in substrate configuration solar cells.