Materials For Solar Cell Applications Research Articles

Strong band filling induced significant excited state absorption in MAPbI3 under high pump power

Perovskite has been considered as promising material for solar cell application. Understanding the carrier dynamics in perovskite material plays a vital role for further improvement of the power conversion efficiency of solar cells. In this article, carrier dynamics of MAPbI3 under different pump powers have been investigated by ultrafast pump-probe transient absorption spectroscopy. Complete processes of carrier cooling and recombination under different pump powers have been characterized and compared carefully. It is found that a significant carrier band filling happened during cooling process under high pump power, which results in a strong excited state absorption at the photon energy of 2.353 eV. High carrier density induced strong Auger effect appears not only in the band edge but also the higher conduction band. And subsequently, a large part of carriers keeps hot for more than 5 ns indicating that MAPbI3 is meaningful for hot carrier extraction in solar cells. A critical carrier concentration of 9.32 × 1017 cm−3 has been determined at which Auger effect starts to work. It could provide some guidance for perovskite solar cell application.

Optimization of ZnO doped TiO2 nanopillars as photoanode for dye sensitized solar cells

Abstract Recent advances in nanotechnology have contributed to the development of engineered nanoscale materials as innovative prototypes to be used for various applications due to their unique features, including a large surface area, structural and optical properties. The introduction of low-cost, high-efficiency Dye Sensitized Solar Cells (DSSCs) have emerged as a potential alternative to the conventional thin film solar cells. In this work, hierarchical nanopillar layers of ZnO/TiO2 grown on TiO2 seed layer were synthesized successfully using a simple and cost- effective Spin coating and Hydrothermal methods. The synthesized sample was characterized by XRD, HR-SEM, UV-DRS, BET and Photoconductivity analysis. The XRD analysis reveals the structure and crystalline nature of the synthesized samples and the crystallite size was found to be 83 nm. The morphology and the average particle size of the synthesized sample were examined by the HR-SEM analysis from which the value was estimated to be 84 nm. UV-DRS analysis gives the absorbance spectrum of the sample in which the absorbance peak is located at 203 nm. Kubelka-Munk function was used to calculate the optical band gap which was found to be 2.7 eV. BET analysis indicates that the specific surface area of the sample with 25.29 m2/g and the field dependent dark and photoconductivity studies recorded greater conductivity owing to factors such as higher surface area and good optical studies. These results strongly suggest that the synthesized sample would be a promising material for solar cell applications especially as photoanode in DSSCs.

Fullerene-Based Interlayers for Breaking Energy Barriers in Organic Solar Cells.

Organic solar cells (OSCs) are lightweight, flexible, and have easy solution processability, thus making them advantageous for large-area device fabrication. The interlayer materials between the electrodes and organic active layer are vital elements for device fabrication. Recently, solution-processable fullerene derivatives have been studied intensively as efficient electrode interlayer materials for solar cell applications. In this Minireview, we summarize recent advances using fullerene derivatives as interlayers in OSCs. The examples include fullerene interlayers from small molecules to polymers, and to organic composites or organic/inorganic hybrid materials. We focus on the comprehensive efforts in developing fullerene-based interlayers and present the understanding of multiple functionalities of these materials as cathode interlayers in bulk hetero-junction (BHJ) OSCs. Our motivation is to describe our current understanding, recent progress, and outstanding issues of fullerene interlayers in OSCs, and propose future potential directions and opportunities.

Novel synthesis of Cu2CoSnS4-carbon quantum dots nano-composites potential light absorber for hybrid photovoltaics

A novel and simple synthesis of the absorber layer is indispensable in order to reduce the cost and processing of quantum solar cells. In this work, we developed novel Cu2CoSnS4-carbon quantum dot (CCTS:CQD) nano-composite as an absorbing material for solar cell applications. CCTS:CQD nano-composites were prepared by direct pyrolysis of CCTS precursors and citric acid. The proportions of citric acid precursor to CCTS were varied from 0.1 to 0.7. The properties of the synthesized nano-composite were studied using a UV–vis spectrophotometer in the wavelength range of 300–900 nm. CCTS:CQD has a property of dynamic photoluminescence that depends on the excitation wavelength. The results of the x-ray diffraction revealed that the CCTS:CQD nano-composites were predominantly polycrystalline in nature. The formation of CCTS:CQD was confirmed by a high-resolution transmission electron microscope (HRTEM), which exhibits the size ∼3 nm. The thin films of CCTS:CQD nano-composites were deposited on glass/ITO substrates by spray pyrolysis technique at 170 °C. Current–voltage (I–V) measurements carried out in dark and light conditions revealed CCTS: CQD thin films with good photo-response. The purpose of the present study is to develop CCTS: CQD nano-composite p-type absorber layer suitable for thin film solar cells.

Performance enhancement of CIGS thin-film solar cells with a functional-window NiO thin layer

Abstract Cu(In1-χGaχ)Se2 (CIGS) films have been considered as promising materials for solar cell applications owing to high absorption coefficient, bandgap grading, flexibility, and high conversion efficiency. In particular, the bandgap grading has been widely researched as a back surface field effect to reduce the carrier recombination. Recently, the front surface field has been researched by the application of a transition metal oxide (TMO) to increase the power conversion efficiency (PCE). Among them, NiO is an outstanding TMO layer because of its wide bandgap (∼3.7 eV), stable cubic structure, the low electron affinity of 1.33–1.85 eV and p-type characteristics. Consequently, the application of the NiO layer has been researched on the CIGS solar cells as an effective electron blocking barrier, which is to suppress the carrier recombination. Even though much research has proceeded on the versatile properties of the NiO, there is rarely research to apply the NiO layer on the CIGS solar cells yet. In this study, we introduced the application of NiO layer deposition on the CIGS solar cell to improve the PCE. The NiO layer (20 nm) was deposited on the CIGS solar cell using the E-beam evaporator system at room temperature. We investigated the effect of the application of the p-NiO layer on the CIGS solar cells, comparing the efficiencies and dark J-V curves. These results are in good agreement with time-resolved photoluminescence measurements on the carrier lifetime. The PCE of the device with the p-NiO layer was measured as 16.35% and the PCE of the device without the p-NiO layer was measured as 15.81%. After the application of the p-NiO layer, we gained the improvement with 0.54% of the PCE.

Effects of boron and hydrogen doping on the enhancement of photoresponsivity and photoluminescence of BaSi2 epitaxial films

BaSi2 is an emerging material for solar cell applications. We investigate the defect properties of 0.5 μm thick BaSi2 films by photoresponse and photoluminescence (PL) measurements. The photoresponsivity of BaSi2 films measured under a bias voltage of 0.3 V applied between the front-surface and rear-surface electrodes at room temperature was enhanced by doping B atoms of the order of 1018 cm−3. Much further enhancement was achieved after atomic H supply for 5 min by a RF plasma gun. These results suggest that the doping of B and H atoms is an effective means to passivate the defects in BaSi2 films. PL measurements at 8–9 K highlighted the existence of localized states within the bandgap. Measured PL spectra were decomposed into two or four Gaussian curves. The enhancement of photoresponsivity was ascribed to the decrease of deep defect levels.

Fabrication and characterization of perovskite (CH3NH3PbI3) solar cells

Perovskite material has emerged as an attractive strategy to efficiently convert light into electricity. We are using organic–inorganic–halide CH3NH3PbI3 as a heart of solar cells with the device structure: FTO/compact TiO2/mesoporous TiO2/perovskite/spiro-MeOTAD/Au. The 1.51 eV energy bandgap is in the perovskite material which is great for power conversion efficiency. We are studying the degradation of perovskite solar cell device in the presence of UV light and white light, for a clear understanding of degradation we are measuring I–V characteristics and dielectric properties under various conditions. The schematic energy level diagram shows that electron–hole transport in the tuneable energy band of the intermediate layer of the device. Due to high light absorption, photovoltaic and diffusion length properties of perovskite is the most appropriate material for solar cell application.

Effect of mixed halide contents on structural, electronic, optical and elastic properties of CsSnI3−xBrx for solar cell applications: first-principles study

In this study, structural, electronic, optical and elastic properties of CsSnI3−xBrx perovskites are investigated by full potential linearized augmented plane wave method (FP-LAPW) with exchange correlation functionals GGA-PBE and GGA-mBJ as implemented in Wien2k. The calculated structural parameters for all compositions are in good correlation with literature. The band structures and density of states (DOS) are calculated by GGA which indicated that all these alloys have direct band gap. Furthermore, the band gaps are also calculated by employing modified Beck-Johnson’s (mBJ) exchange potential. The obtained band gaps with this method are found to be improved as compared to GGA. The calculated optical parameters show that these materials have the competency for light absorption and to retain it. These characteristics make them promising materials for solar cell applications. The elastic constants have also been calculated which revealed that all these compounds have ductile nature. The mixed halide contents are pioneered in this study and therefore, no data is in hand for estimation.

WS2: A New Window Layer Material for Solar Cell Application

Radio frequency (RF) magnetron sputtering was used to deposit tungsten disulfide (WS2) thin films on top of soda lime glass substrates. The deposition power of RF magnetron sputtering varied at 50, 100, 150, 200, and 250 W to investigate the impact on film characteristics and determine the optimized conditions for suitable application in thin-film solar cells. Morphological, structural, and opto-electronic properties of as-grown films were investigated and analyzed for different deposition powers. All the WS2 films exhibited granular morphology and consisted of a rhombohedral phase with a strong preferential orientation toward the (101) crystal plane. Polycrystalline ultra-thin WS2 films with bandgap of 2.2 eV, carrier concentration of 1.01 × 1019 cm−3, and resistivity of 0.135 Ω-cm were successfully achieved at RF deposition power of 200 W. The optimized WS2 thin film was successfully incorporated as a window layer for the first time in CdTe/WS2 solar cell. Initial investigations revealed that the newly incorporated WS2 window layer in CdTe solar cell demonstrated photovoltaic conversion efficiency of 1.2% with Voc of 379 mV, Jsc of 11.5 mA/cm2, and FF of 27.1%. This study paves the way for WS2 thin film as a potential window layer to be used in thin-film solar cells.

Three-step growth of highly photoresponsive BaSi2 light absorbing layers with uniform Ba to Si atomic ratios

Barium disilicide (BaSi2) shows great promise as a light absorbing material for solar cell applications. Thus, it is important to form high-quality BaSi2 films with a low defect density. We previously found that the photoresponsivity of a-axis-oriented BaSi2 epitaxial films was enhanced drastically when formed under Si-rich conditions by molecular beam epitaxy. However, the degree of a-axis crystal orientation normal to the sample surface was degraded. In this work, we investigated the origin of this degradation by cross-sectional transmission electron microscopy (X-TEM). It was found that excess Si atoms in BaSi2 films diffused out and precipitated around the BaSi2/Si interface, resulting in the formation of Si layers with an interface roughness of 0.2–0.3 μm when grown under Si-rich conditions. Furthermore, extended defects stemming from such rough interface regions were detected by deep level transient spectroscopy, and they acted as hole trap defects. To achieve high photoresponsivity in BaSi2 films under Si-rich conditions while avoiding such Si precipitation, we proposed a three-step growth method for BaSi2 films. X-TEM observations confirmed uniform Ba to Si atomic ratios throughout the entire layer and smooth BaSi2/Si interfaces. In addition, relative to films grown by the conventional two-step method, the a-axis orientation was improved significantly, and the photoresponsivity increased by approximately five times to reach 0.5 A/W at a wavelength of 800 nm under a bias voltage of −0.1 V. This corresponds to an external quantum efficiency above 90%.

Synthesis, thermal stability and structural transition of cubic SnS nanoparticles

Recently identified cubic polymorph of SnS (SnS-CUB) is a promising low-cost material for solar cell applications. We report on the thermal stability, structural and optical properties of SnS-CUB nanoparticles. The average crystallite size of cubic SnS nanoparticles synthesized by wet chemical method at 20 °C is about 34.9 nm and unit cell lattice parameter a = 11.59 Å. We found that cubic phase remained structurally stable up to 400 °C even though sulfur is partially re-evaporated. The sample annealed at 450 °C contains both cubic and orthorhombic phases. When the annealing temperature is increased to 500 °C, the sample completely transforms to orthorhombic structure. Raman spectroscopy showed the formation of minor secondary phases Sn2S3 and SnO2 at temperatures ≥500 °C. Three distinct regions of weight loss are observed in thermogravimetric curve (TGA) of cubic SnS nanoparticles; around 300 °C, 600 °C and 800 °C. Weight loss of 10% observed near 600 °C was due to rapid re-evaporation of sulfur from SnS. Annealing at 500 °C decreases the direct optical bandgap value 1.68 eV–1.3 eV (direct), 1.0 eV (indirect) is also an indication of the structural transition of SnS-CUB to orthorhombic SnS. Cubic SnS nanoparticles were strongly absorbing light photons in the visible wavelength range of 400 nm–700 nm. The orthorhombic SnS with an indirect bandgap of 1 eV has extended the absorption edge to 1000 nm. By combining both cubic and orthorhombic SnS, the absorption can be extended to a wide wavelength range.

Synthesis of Cu2ZnSnSe4 from nitrate and selenite inks for use as an absorbent layer in the design of solar cells

This research was conducted to identify two acceptable precursors and methods of synthesis for the manufacture of photovoltaic cells. The kesterite Cu2ZnSnSe4, a promising material for solar cell applications, was synthesized from metal salts of Cu, Zn, Sn, and Se, by two low-cost routes: the direct dissolution of metal nitrates, and coprecipitation of selenites. In both cases, inks were obtained and deposited as thin-films by the Doctor Blade technique on glass substrates coated with molybdenum. The films were annealed in an oven at 550 °C by 30 minutes. The phases of each thin film were analyzed by X-ray diffraction and Raman scattering. The morphology and the thickness of the layers were observed using a scanning electron microscope. The optical band gap was determined by ultraviolet-visible spectroscopy and the Tauc equation. The results confirmed the main phase of kesterite material, consistent with a tetragonal crystalline system oriented along the plane (112). These values are consistent with those found by Raman spectroscopy, where the main vibrational mode was identified at 173 cm−1 and 196 cm−1, characteristic of mode A vibration, and 243 cm−1 of mode B vibration; typical of kesterite. Simultaneously, a band gap of 0.89 eV was identified. These results demonstrate the effectiveness of the selenite’s coprecipitation method for synthesis of kesterite, without evidence of secondary phases. This determines the possibility of using this material in solar cell applications.

Thin Film of Perovskite (Mixed-Cation of Lead Bromide FA1−xMAxPbBr) Obtained by One-Step Method

Perovskite materials for solar cell applications were prepared by a one-step method. In the following work, the spin coating technique was used for organic–inorganic hybrid perovskite formamidinium lead tribromide (FAPbBr3), methylammonium lead tribromide (MAPbBr3) and formamidinium methylammonium lead tribromide (FA1−xMAxPbBr3).Thin films of mixed FA1−xMAxPbBr3 (x = 0–1) perovskites deposited on indium tin oxide glass substrates were obtained by mixing FAPbBr3 and MAPbBr3 in different proportions. Structural x-ray diffraction (XRD), morphological (Scanning Electron Microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) and optical (uv–visible spectroscopy (UV–Vis) proprieties were investigated for all synthesized perovskites as a function of the MA/FA ratio. The (XRD) analysis shows the formation of a cubic-phase perovskite with space group Pm-3 m in the composition range 0 ≤ x ≤ 1. High absorbance levels were obtained in the infrared region 500-900 nm for mixed perovskites FAMAPbBr3. The estimated energy band-gap from the absorbance spectral measurements for FAMAPbBr3 thin films was in the range of 2.2 eV for FAPbBr3 and 2.3 eV for MAPbBr3, respectively. The photoluminescence emission of mixed FA/MA perovskite thin films was located in intermediate values between 580 nm and 555 nm.

Improved Charge Separation and Photovoltaic Performance of BiI3 Absorber Layers by Use of an In Situ Formed BiSI Interlayer

Stable and nontoxic bismuth iodide (BiI3) is emerging as a promising absorber material for solar cell applications as it possesses favorable optical properties such as a narrow bandgap (1.7 eV) and...

Energetics, Structures, and Phase Transitions of Cubic and Orthorhombic Cesium Lead Iodide (CsPbI3) Polymorphs

Cesium lead iodide (CsPbI3) perovskite has shown great potential as a light absorbing material for solar cell applications. Despite intense research leading to increasing power conversion efficiency, a major problem concerning CsPbI3 lies in the long term stability and interconversion between different CsPbI3 polymorphs, a subject barely studied from the thermodynamic perspective. We report the formation enthalpies of two CsPbI3 polymorphs, α and δ CsPbI3, using a combination of room temperature solution calorimetry in dimethyl sulfoxide (DMSO) and differential scanning calorimetry. We show that both polymorphs are stable with respect to their binary halides and confirm that the α-phase is a high temperature polymorph, metastable under ambient conditions. This work sheds light on patterns in polymorphism, possible decomposition reactions, materials stability, and compatibility within halide perovskites and related systems. Thermodynamic instability near ambient temperature of functional perovskites may be a general phenomenon related to their vibrational density of states.

Imaging and Mapping Characterization Tools for Perovskite Solar Cells

AbstractPerovskite solar cells (PSCs) have attracted much attention as efficiencies have gone beyond 24%. To achieve these impressive numbers, the PSC scientific community is working to improve the perovskite optoelectronic properties. Imaging and mapping characterization techniques have been widely used to understand the fundamental properties that allow lead halide perovskites to achieve high performance. In this review, these techniques are evaluated, from simple tools, such as electron microscopy, to more complex systems that include atomic force microscopy, synchrotron‐based X‐ray mapping, and ultrafast and photoluminescence mapping. These tools have helped understand lead halide perovskites and their impressive optoelectronic properties, which make them outstanding materials for solar cell applications.

Fabrication of Sulfur‐Incorporated Bismuth‐Based Perovskite Solar Cells via a Vapor‐Assisted Solution Process

Methylammonium (MA) bismuth iodide ((CH3NH3)3Bi2I9) is a promising perovskite material for solar cell application considering the air stability and the nontoxic lead‐free molecular constitution. However, the further improvement of the device performances is prohibited by the wide bandgap (≈2.1 eV) and unsatisfied crystallinity of the (CH3NH3)3Bi2I9 films. Herein, a developed low‐pressure vapor‐assisted solution process (LP‐VASP) method is applied to obtain the sulfur‐incorporated bismuth‐based perovskites films. Due to the presence of sulfur, both the crystal quality and the energy band property are improved effectively in the as‐fabricated lead‐free perovskite films. After a systematic study of the influence of the reaction time on the device performances, the optimized reaction time is found to be 30 min, under which, the sulfur‐incorporated MA3Bi2I9‐2xSx perovskite films exhibit a reduced bandgap of 1.67 eV and a compact morphology. The corresponding optimal PCE reaches 0.152%. This study provides a new way for the incorporation of sulfur in the lead‐free bismuth‐based perovskite solar cells.

Photovoltaic and spectroscopic characteristics of perovskite/TiO2 heterostructure photoanodes for improving the efficiency of dye sensitized solar cells.

Perovskite-type ternary oxide nanostructured materials have gained great attention in recent years as promising materials for solar cell applications. However these ternary oxides have failed to be applied as a working electrode in DSSCs due to its poor performance and its inability to bind dye molecules to the surface. A heterostructure perovskite/TiO2 photoactive electrodes is a new strategy to improve the photon-to-current efficiency (PCE) of DSSCs. In this paper, BaZrO3 (BZ), BaTiO3 (BT) and nanocomposite [1:1] molar% from BaTiO3-BaZrO3 perovskite nanostructured materials synthesized via sonochemical sol-gel methods, are coated on the top of the TiO2 photoactive electrode. This heterostructured (perovskite/TiO2) photoelectrode has been applied for improving the performance of dye-sensitized solar cells (DSSCs). The crystallographic, morphological and optical characteristics of the different prepared perovskite nanomaterials has been investigated by XRD, SEM, TEM, Raman and UV-Vis Diffuse reflectance spectroscopic analysis, respectively. Dye-sensitized solar cells based on the different heterostructure perovskite/TiO2 electrodes are assembled, and high conversion efficiency (η) are calculated from the current density-voltage (J-V) characteristics of the solar cells. The results show an efficiency enhancement with about ∼22%, 37% and 51% in case of BZ, BTZ and BT respectively. These enhancements is attributed to high refractive index of the perovskite nanoparticles, higher incident photon-to-current conversion yield which is due to greater fraction of light scattered, as well as the less recombination of the photogenerated electrons.

Synthesis and characterization of Cu2CoSnS4 thin film via electrodeposition technique for solar cells

Quaternary compound Cu2CoSnS4 (CCTS) is a potential candidate absorber layer in thin film solar cells to produce clean and inexhaustible energy. In this work the Cu2CoSnS4 (CCTS) thin film was synthesized for the first time by co-electrodeposition of Cu–Co–Sn–S precursors on Molybdenum substrate, followed by a high temperature (500 °C) sulfurization under Argon atmosphere. The potential deposition (−0.95 V/SCE) was determined from cyclic voltammetry . The structure, composition and morphology of the CCTS thin film is characterized in detail by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and energy dispersion spectroscopy. The p-type conductivity of CCTS thin film was confirmed using Mott–Schottky analysis and the band gap value was evaluated to be 1.56 eV, which makes CCTS a promising material for solar cell applications.

Atomic-Scale Tailoring of Organic Cation of Layered Ruddlesden-Popper Perovskite Compounds.

Layered Ruddlesden-Popper (RP) phase perovskite compounds have emerged as promising photovoltaic materials for solar cell applications, but they suffer from poor absorption and strong exciton-binding energy. Herein, fluoro-, chloro-, and bromo-substitutions on the 4-position of the phenyl group in the component C6H5CH2CH2NH3+ (PEA+) are designed and synthesized to investigate their effect on the layered RP type H-PEA2MA2Pb3I10 (MA = CH3NH3) perovskite as an example. Single-crystal X-ray diffraction and temperature-dependent photoluminescence spectroscopy characterization reveal the electron-withdrawing halogen in organic cations decreases the distortion of inorganic sheets and significantly reduces the impact of two-dimensional quantum and dielectric confinement. This is further verified with an increased visible absorption and lower exciton-binding energy for these new layered RP-type perovskite compounds. A planar structured perovskite solar cell using an F-PEA2MA2Pb3I10 layer achieves a power conversion efficiency of 5.8%, which is better than that of the reference H-PEA2MA2Pb3I10.