Absorber Layer In Solar Cells Research Articles

Evaluation of the optical properties of the lead-free mixed-halide iron perovskite CH3NH3FeI2Br for application in solar cells: A computational study

Performance of the proposed lead-free mixed halide iron perovskite CH3NH3FeI2Br as the light absorber layer of the perovskite solar cells is evaluated based on the analysis of the calculated optical properties. Crystal structure of this mixed halide iron perovskite is optimized at spin-polarized DFT GGA-PBE/FP-LAPW+lo level of theory. Structural analysis shows that the optimized unit cell parameters of this CH3NH3FeI2Br perovskite are all smaller than their corresponding values for the pure iodide iron perovskite CH3NH3FeI3. Thermodynamic analysis based on the total SCF energies calculated for the CH3NH3FeI2Br, CH3NH3FeI3, I2 and Br2 lattices shows also that the mixed halide iron perovskite CH3NH3FeI2Br is more stable than the pure iodide iron perovskite CH3NH3FeI3 by 1477.5 kJmol−1. Band structure, density of states and band gaps are calculated with the GGA-PBE(mBJ)/FP-LAPW+lo method. Analysis of the results show that the mixed halide iron perovskite CH3NH3FeI2Br is a direct band gap semiconductor having band gaps of 3.041 and 0.689 eV for its spin-up and spin-down states, respectively. The absorption spectrum calculated for the mixed halide iron perovskite MAFeI2Br and its corresponding Brewster angles calculated for the TiO2/perovskite and perovskite/spiro interfaces, the proposed mixed halide iron perovskite MAFeI2Br can be regarded as a promised candidate for application as light-harvesting layer of perovskite solar cells due to its good optical performance in the 500–630 nm range of wavelengths of the sunlight spectrum. Stability of the proposed CH3NH3FeI2Br perovskite is also validated based on the analysis of the calculated octahedral and Goldschmidt tolerance factors (0.465 and 1.009, respectively).

A thin Cu interlayer-mediated control of phase evolution of Cu2ZnSnS4 thin films grown by RF magnetron sputtering of a single elementary target with high white light sensitivity

Although sputter deposition from a single target to prepare Cu2ZnSnS4 (CZTS) thin films appears attractive, it must suppress the growth of secondary phases that detrimentally affect performance of CZTS based thin film solar cells. Here we demonstrate a rational strategy for deposition of phase pure kesterite CZTS films by RF magnetron sputtering using a single target prepared from elemental powders via a thin Cu interlayer-mediated control of phase evolution. The films grown from a target of stoichiometric elemental proportion were Cu poor that determined the reaction pathway during sulfurization and resulted in growth of spurious phases despite a large variation in the sulfurization configuration. Inserting a 195 nm thick Cu interlayer between successively sputtered precursor layers provided improved compositional stability through thermally activated diffusion of Cu from the intermediate layer towards both the sides and resulted in the formation of kesterite CZTS even at a modest sulfurization temperature of 500 °C. The obtained phase-pure films have a bandgap of ~1.58 eV. The films show excellent photoresponse behavior characterized by increase in current by three orders of magnitude at a bias of 3 V upon white light illumination, typically that required for a potential absorber layer in thin film solar cells.

Precise Definition of a “Monolayer Point” in Polymer Brush Films for Fabricating Highly Coherent TiO2 Thin Films by Vapor-Phase Infiltration

In this work, we show that in order to fabricate coherent titania (TiO2) films with precise thickness control, it is critical to generate a complete polymer brush monolayer. To date, demonstrations of such dense polymer monolayer formation that can be utilized for inorganic infiltration have been elusive. We describe a versatile bottom-up approach to covalently and rapidly (60 s processing) graft hydroxyl-terminated poly(2-vinyl pyridine) (P2VP-OH) polymers on silicon substrates. P2VP-OH monolayer films of varying thicknesses can subsequently be used to fabricate high-quality TiO2 films. Our innovative strategy is based upon room-temperature titanium vapor-phase infiltration of the grafted P2VP-OH polymer brushes that can produce TiO2 nanofilms of 2-4 nm thicknesses. Crucial parameters are explored, including molecular weight and solution concentration for grafting dense P2VP-OH monolayers from the liquid phase with high coverage and uniformity across wafer-scale areas (>2 cm2). Additionally, we compare the P2VP-OH polymer systems with another reactive polymer, poly(methyl methacrylate)-OH, and a relatively nonreactive polymer, poly(styrene)-OH. Furthermore, we prove the latter to be effective for surface blocking and deactivation. We show a simple process to graft monolayers for polymers that are weakly interacting with one another but more challenging for reactive systems. Our methodology provides new insight into the rapid grafting of polymer brushes and their ability to form TiO2 films. We believe that the results described herein are important for further expanding the use of reactive and unreactive polymers for fields including area-selective deposition, solar cell absorber layers, and antimicrobial surface coatings.

Graphene to Advanced MoS2: A Review of Structure, Synthesis, and Optoelectronic Device Application

In contrast to zero-dimensional (0D), one-dimensional (1D), and even their bulk equivalents, in two-dimensional (2D) layered materials, charge carriers are confined across thickness and are empowered to move across the planes. The features of 2D structures, such as quantum confinement, high absorption coefficient, high surface-to-volume ratio, and tunable bandgap, make them an encouraging contestant in various fields such as electronics, energy storage, catalysis, etc. In this review, we provide a gentle introduction to the 2D family, then a brief description of transition metal dichalcogenides (TMDCs), mainly focusing on MoS2, followed by the crystal structure and synthesis of MoS2, and finally wet chemistry methods. Later on, applications of MoS2 in dye-sensitized, organic, and perovskite solar cells are discussed. MoS2 has impressive optoelectronic properties; due to the fact of its tunable work function, it can be used as a transport layer, buffer layer, and as an absorber layer in heterojunction solar cells. A power conversion efficiency (PCE) of 8.40% as an absorber and 13.3% as carrier transfer layer have been reported for MoS2-based organic and perovskite solar cells, respectively. Moreover, MoS2 is a potential replacement for the platinum counter electrode in dye-sensitized solar cells with a PCE of 7.50%. This review also highlights the incorporation of MoS2 in silicon-based heterostructures where graphene/MoS2/n-Si-based heterojunction solar cell devices exhibit a PCE of 11.1%.

Understanding effects of defects in bulk Cu2ZnSnS4 absorber layer of kesterite solar cells

One of the main causes of degraded performance is the defects in the bulk Cu2ZnSnS4 absorber layer of the kesterite solar cells. In this study, a numerical simulator SCAPS-1D used to understand the effects of each point of antisite defects with the presence of the band tail on the electrical characteristics of Cu2ZnSnS4 solar cells step-by-step. The effects of capture cross-section of SnZn deep multilevel defect and defect concentration of CuZn + ZnCu on cell performances have been analyzed. The results highlight that the control of capture cross-section of the multilevel defects is an important key to take into account for further improvements of Cu2ZnSnS4 solar cell performance.

EFFECT OF TIN PRECURSORS ON THE DEPOSITION OF Cu2ZnSnS4 THIN FILMS

Cu2ZnSnS4 is a potential compound semiconducting material for solar absorber layer in thin film heterojunction solar cells. Chemical spray pyrolysis technique has been successfully employed to deposit these thin films using two different tin precursors. Thin films were characterized by studying their structural, composition, electrical and optical properties. X-ray diffraction pattern reveals that these films exhibit polycrystalline nature with kesterite structure. Lattice parameters of Cu2ZnSnS4 films are found to be a = b = 0.544 nm and c = 1.084 nm. Optical band gap, evaluated from spectral transmittance data, is close to ideal energy gap (1.5 eV) exhibit highest conversion efficiency. Optical absorption coefficient of these films is ≥ 104 cm-1 . These films exhibit p-type nature. A humble attempt is made to fabricate a typical heterojunction Cu2ZnSnS4 thin film solar cell.

Enhanced magnetic, antibacterial and optical properties of Sm doped ZnO thin films: Role of Sm doping

Abstract Thin films of Sm3+ ions doped ZnO were prepared by dip coating method. To enhance the oxygen vacancy in the host ZnO lattice and obtain crystallinity, the thin films were annealed at 400 °C for 2 h in air. X-ray diffractions (XRD) study displays the hexagonal wurtzite structure of ZnO with crystallite size in the range of 27.37–24.21 nm. The induced carrier concentration, intrinsic defects and oxygen vacancies produced a blue shift in the band gap (Eg) with an increase in Sm doping percentage. The surface morphology is granular with slight agglomeration. Thin films have shown violet photoluminescence. The emissions intensity can be tailored by increasing the Sm percentage which is due to the increase in defect concentration as well as find application in optoelectronic devices. Room temperature ferromagnetism is recorded in the thin films. Hysteresis show that 1 at. wt. % Sm doped ZnO has larger saturation magnetization than 5 at. wt. % Sm doped thin films. The work has established that rare earth element doping in ZnO produces diluted magnetic semiconductors which can be part of absorber layer of solar cell, to store data in memory devices and optoelectronics applications. Antibacterial studies were conducted for Staphylococcus aureus (S. Aureus), klebsiella pneumonia (K. B), Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) bacterial strains by applying the agar well diffusion method to suspension containing undoped ZnO and Sm doped ZnO nanoparticles. The enhancement in the zone of inhibition with an increase in samarium exhibits high antibacterial activity. The results predict that Sm doped ZnO is a good possibility of food packing, removal of the tumor, treatment of pneumonia and a diagnosis of malign diseases.

Real-Time Optimization of Anti-Reflective Coatings for CIGS Solar Cells.

A new method combining in-situ real-time spectroscopic ellipsometry and optical modeling to optimize the thickness of an anti-reflective (AR) coating for Cu(In,Ga)Se2 (CIGS) solar cells is described and applied directly to fabricate devices. The model is based on transfer matrix theory with input from the accurate measurement of complex dielectric function spectra and thickness of each layer in the solar cell by spectroscopic ellipsometry. The AR coating thickness is optimized in real time to optically enhance device performance with varying thickness and properties of the constituent layers. Among the parameters studied, we notably demonstrate how changes in thickness of the CIGS absorber layer, buffer layers, and transparent contact layer of higher performance solar cells affect the optimized AR coating thickness. An increase in the device performance of up to 6% with the optimized AR layer is demonstrated, emphasizing the importance of designing the AR coating based on the properties of the device structure.

Effect of substrate type on RF magnetron sputtered CuInS2 thin films properties based on nanoparticles synthesized by solvothermal route

Stereometric and fractal analyses have been performed on the three-dimensional surface microtexture of the sputtered copper indium disulfide films on various substrates. The target used in the sputtering was made from nanoparticles synthesized by the solvothermal route. The effects of substrate on structural and morphological properties of the films were investigated. The obtained CuInS2 films were polycrystalline textured, preferentially oriented in (112) crystallographic direction. Also, the (112) peak intensity changes with the substrate type. From atomic force microscopy (AFM) analysis, it can be concluded that the growth of the film on molybdenum substrate is promising for photovoltaic applications particularly as absorber layer in solar cells. The surface microtexture characterization in terms of surface dimensions, volume, curvature, shape was analyzed according to ISO 25,178–2: 2012 standard.

Structural, electronic and optical properties of Ag2MgSn(S/Se)4 quaternary chalcogenides as solar cell absorber layer: An Ab-initio study

In this work, generalized gradient approximation (GGA) and the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional within the framework of density functional theory (DFT) are used to investigate the structural, electronic and optical properties of Ag2MgSn(S/Se)4 quaternary chalcogenides in kesterite and stannite phases. The kesterite and stannite phases of Ag2MgSn(S/Se)4 are optimized and the values of lattice constants are calculated. The predicted energy bandgaps are found to be direct in nature along the Γ direction, with highest bandgap energy of less than 1.64 eV for Ag2MgSnS4 in kesterite phase. The total and partial density of states are analysed in detail. The optical properties such as imaginary and real parts of dielectric function, refractive index, reflectivity and extinction coefficient are also discussed. Further, in order to understand the light trapping capacity, we examine the absorption coefficients of Ag2MgSnS4 and Ag2MgSnSe4 materials and explore their applicability as solar cell absorber layers. The predicted values of all parameters will help researchers to carry out further investigations on these materials for photovoltaic applications.

Role of ZnS Particles in the Performance of Cu2ZnSnS4 Thin Film Solar Cells: A Comparative Study by Active Control of Zinc Deposition in Coevaporated Precursors

Formation of ZnS particles in the Cu2ZnSnS4 (CZTS) light absorber layer of CZTS solar cells may impede the photocarrier collection as well as the open circuit voltage. Coevaporation of Cu, Zn, Sn, and S elements can provide a uniform and well‐mixed Cu–Zn–Sn–S precursor at atomic level, yet the annealing/sulfurization process does not preserve such elemental distribution. The Zn element in the formed CZTS absorber thin films from such a uniform precursor distributes unevenly, especially aggregating near the rear interface, and thus deteriorates the film quality. Herein, the movement pathway of the Zn element in the coevaporated precursor during annealing is investigated through energy dispersive X‐ray spectroscopy (EDX) mapping and secondary ion mass spectroscopy (SIMS) profiling. With the understanding of the segregation behavior of the Zn element, an active manipulation of the initial distribution of Zn in the precursor is accordingly designed to effectively alleviate the accumulation of Zn near the rear Mo/CZTS interface and therefore improve the crystalline quality of the absorber. The results suggest that properly controlling the precursor.

Enhanced recombination next to laser-patterned lines in CIGSe solar cells revealed by spectral and time-resolved photoluminescence

Laser-based patterning of CIGSe solar cell absorber layers for monolithic series connection by nanosecond (ns) and picosecond (ps) laser pulses introduces material modifications in the vicinity of the patterned lines, which affect the CIGSe composition, the electrical properties, the extent of the dead area and finally the efficiency of the complete solar cell. Here, spectral and time-resolved photoluminescence is used to show that Cu vacancies and anti-sites are formed next to the edges of the scribe lines, which lead to the formation of additional energy states in the band gap near the valence band edge. A significant reduction in charge carrier lifetime is noted as the scribed lines are approached from unaffected areas of the material. Since this effect is absent in the mechanical needle patterning, it can clearly be attributed to the influence of the laser pulses. Despite the laser-induced material modification, laser-based CIGSe patterning outperforms needle-based patterning. Advantages regarding the width of the affected edge areas were observed when using ns pulses instead of ps pulses, which could be due to the lower peak intensities.

Annealing time effect on CIGS thin films

Chalcopyrite copper indium gallium (di)selenide (Cu(In, Ga)Se2 (CIGS)) thin film has been examined as an absorber layer for solar cells because of its suitable absorption value, stability and economy in manufacture. CIGS thin films belong to the I–III–VI2 group of the periodic table with the appropriate direct bandgap (1.5 eV). In this study, CIGS thin films were annealed at ∼200°C for four different annealing times (15, 30, 45 and 60 min) to investigate the effect of the annealing time on the crystalline structure and optical properties of CIGS thin films prepared by using the sol–gel dip-coating technique. CIGS thin films annealed at ∼200°C for 60 min were found to have the best structural and optical properties in this study. As the crystallite size increased with the rise in the annealing time, the lattice strain decreased, indicating the elimination of crystallite defects in the CIGS thin-film structure. Hence, the structural changes affected the optical properties slightly and the rise in the optical absorbance (A%) resulted in a decrease in the optical transmittance (T%).

Fermi Energy Limitation at β-CuGaO2 Interfaces Induced by Electrochemical Oxidation/Reduction of Cu

β-CuGaO2 possesses a direct band gap of 1.5 eV and is therefore expected as a suitable light absorber layer for thin-film solar cells. To evaluate the potential of β-CuGaO2 as a light absorber, the...

Optimization of the Electrical Characteristics of Cadmium Telluride Based Thin Layer Solar Cell According to Thickness and Gap Energy

In the quest for better photovoltaic performance, we simulated the CdTe-based thin film solar cell in ITO/CdS/CdTe/Mo structure with SCAPS (Solar Cell Capacitance Simulator). SCAPS model makes possible to study the effect of the thickness of layers and the gap energy (Eg) of each layer (CdTe, CdS and ITO) on the electrical characteristics of outputs such as open-circuit voltage (Voc), short-circuit current density (Jsc), Form Factor (FF) and efficiency (&eta) of the cell. The results of the simulations were in good agreement with those of the literature and revealed that increasing the thickness of the ITO window layer and of the CdS buffer cell layer reduces the photovoltaic efficiency. Conversely, the conversion rate increases with the thickness of the CdTe absorbent layer. The optimized values of layer thicknesses and energy gap of the absorber layer of the CdTe solar cell provide good photovoltaic performance with an optimal efficiency of 22%.

Impact of silver dopants on structural, morphological, optical, and electrical properties of copper-zinc sulfide thin films prepared via sol-gel spin coating method

Abstract In recent days, Eco-friendly nano-composite thin film employed as an absorber layer in solar cells is one of the most worthy kind of industrial semiconductors and a variety of optoelectronics and optical device applications. Thus, nano-composite samples of copper-zinc sulfide (Cu-Zn-S) embedded with silver dopants (Ag) were perfectly synthesized using 280 °C temperature and low-cost sol-gel spin coating technique without sulfurization. For this objective, several films like pristine (S0) and Ag-doped Cu-Zn-S with different Ag concentrations 0.5% (S1), 1% (S2) and 2% (S3) were deposited on various kinds of substrates like glass, n-type and p-type silicon (Si) with 5 and 8 layer thicknesses. The impact of Ag concentration and the thickness of the prepared film on the surface morphology, structural, electrical, and optical properties of the deposited films on glass substrates were elaborated. It was found that both pristine and Cu-Zn-S films doped with various concentrations of Ag depict the polycrystalline structure of hexagonal and cubic crystal structure using X-ray diffraction. The images of the SEM (scanning electron microscopy) displayed excellent compatibility, homogeneous spreading with a smooth uniform surface, and cover all the areas of the substrates, especially the 1% Ag/Cu-Zn-S film with the structure of less porosity. The results of ICP-OES (inductively coupled plasma-optical emission spectroscopy) and EDS (energy dispersive spectroscopy) were investigated to identify the composition of the forming elements. The optical properties of pristine and Ag-doped films with 5 and 8 layer thicknesses were reported. It was found that for 5 layer deposition at 280 °C, the optical bandgap energy (Eg) reduces from 2.29 eV (S0) to 2.09 eV at 2% Ag/Cu-Zn-S (S3) films. While for 8 layer deposition, the Eg decreases from 2.16 eV (S0) to 1.91 eV at 2% Ag/Cu-Zn-S (S3) films. Hence it can be concluded that the Eg decreases with increasing the thickness of the film, which is in agreement with the achieved results in the literature. In addition, it was observed that the 1% Ag/Cu-Zn-S (S2) film has the lowest resistivity value of 0.66 Ω cm at 280 °C. From all measurements obtained by depositing films on glass substrates, we select the best films to be deposited on n- and p-types Si substrates to study the impact of the n- and p-types silicon substrates on the properties of our films. We also calculated the values of the index of refraction (n), high frequency and optical static dielectric constants (e, e˳) of deposit films on Si and glass substrates through the calculation of Eg as a function of the silver concentrations.

Electrical Properties of Compact Drop-Casted Cu2SnS3 Films

We investigated temperature-dependent electrical conduction of Cu2SnS3 (CTS) thin films in the range of 77–500 K synthesized by drop-casting molecular ink. The films were directly formed by drop-casted molecular ink, consisting of a Cu+2-Sn+2-thiourea complex dissolved in a mixture of ethylene glycol–isopropyl alcohol and annealed. The CTS films have a smooth layer with a compact structure, as revealed by cross-sectional scanning electron microscopy. The films are p-type and show a band gap of 1.18 eV. The electrical conductivity and Hall mobility of the films were found to be 1.1 S/cm and 6.72 cm2 V−1 s−1, respectively. Data from temperature-dependent measurements show hopping and thermally activated conduction below and above 300 K, with an activation energy of ∼ 10 and 90 meV, respectively. Our results suggest that the drop-casted CTS films can be used as an absorber layer in thin film solar cells at an affordable cost.

Extensive investigation of structural, electronic, optical, and thermoelectric properties of hybrid perovskite ( CH 3 NH 3 PbBr 3 ) with mechanical stability constants

Recently, Organometallic halide based perovskites have emanated as an auspicious candidate as a solar cell absorber layer. In this article, we have explored the fundamental properties such as structural, electronic, optical, elastic, and thermoelectric parameters of CH3NH3PbBr3 through first-principles calculations, because it has accomplished the entire criterion to use in photovoltaic and thermoelectric applications. We have used full-potential linearized augmented plane wave method (FP-LAPW) within DFT and implemented in Wien2k. The generalized gradient approximation (GGA) parameterized by Wu-Cohen (WC) has been used to optimize the lattice parameter, while for band gap calculations different exchange-correlation potentials (LDA/GGA) have been used. The band gap up to 2.26 eV has been achieved by doing some appropriate changes in the parameter of TB-mBJ exchange-correlation potential. The nature of band gap is direct and exist at R (0.5 0.5 0.5) symmetry point of the Brillouin zone. All the optical spectral response between 2 and 5 eV is due to the transition of Br 5p with little contribution Pb 5s orbital electrons of VBM to Pb 6p orbitals in CBM and a minor contribution of second band gap components also incorporate. As well as, a high absorption coefficient shows that it may be strongly applied in photovoltaic devices. The orientation of organic cations (CH3NH3)+ has no considerable impact on the band structure formation. To render a solid foundation about the application in the thermoelectric device up to the high-temperature region, the thermoelectric parameters have been discussed at optimal carrier concentration and definite temperature range. The measurement of elastic constants, B/G and Poisson's ratio indicates the ductile nature of CH3NH3PbBr3. To the best of my knowledge, most of the investigations have been discussed first time for this material.

Synthesis of Sb(V) Complexes with Pyridyl Cations and Application for Lead-free Perovskite Solar Cells

Lead halide perovskite has emerged as a promising photovoltaic material due to its excellent power conversion efficiency (PCE). However, the toxicity problem of lead-based perovskite hampers the commercialization of perovskite solar cells. Here, we develop several Sb(V) complexes with pyridyl cations and serve as absorber layer for lead-free perovskite solar cells. The designed complexes were based on 4-tert-butylpyridine (tBP) and N-ethylpyridinium (N-EtPy) cations with bandgaps of 2.01 eV and 1.95 eV, which showed their potential for solar cells and optoelectronic applications. We also found a chemical rule for stable Sb complexes in terms of the bond connectivity of pnictogen-antimony. Initial studies produce a solar cell with a PCE of 0.9% and offer inspiration for further exploration of environment-friendly perovskite families.

Optical characterization study of thin film for PV cell applications

In this investigation n-type CdxZn1-xS and p-type PbS thin films were synthesized using chemical bath deposition (CBD) method for solar cell applications. The thin films were prepared using nitrates of cadmium and thiourea, lead and zinc. Deposition of optimised CdxZn1-xS was complete by CBD at 820 °C, in alkaline circumstances, while that of PbS ended at room temperature and both films at normal atmospheric pressure exploiting aqueous environments. Optical constant appropriate for photovoltaic applications were attempted for and to resolve this, a UV VIS IR spectrophotometer 3700 DUV was utilized. The optical band gap of deposited CdxZn1-xS films range from 2.47 eV (x = 0.6) to 2.72 eV (x = 1.0), and transmittance overhead 79% in the VIS - NIR region for the concentration range of × = 0.6 to 1.0. The band gap enlarged with increasing Zn concentration of the alloy and Cd0.6Zn0.4S sample exhibited the broadest band gap. It is observed that the concentration of zinc increased optical band gap. PbS thin films consumed a band gap of 0.89 eV and a transmittance underneath of 55% appropriate for absorber layers of solar cells. The fabricated photovoltaic cell had a small circuit current, Isc = 0.031 A, exposed voltage, Voc = 0.37 V, efficiency, η = 0.9% and a fill factor, FF = 0.66 inferring that the two materials are suitable for photovoltaic applications particularly in the VIS and IR light spectrum.