Efficient Thin Film Solar Cells Research Articles

Enhancement in the efficiency of Sb2Se3 solar cell with the adding of high electrical concentration CdS:Al film

As a new general photovoltaic, antimony selenide (Sb2Se3) thin-film solar cell is now limited by the open-circuit voltage (Voc). In this study, an ultra-thin CdS:Al film obtained by co-sputtering CdS and Al targets as a N+ layer was employed in Sb2Se3 thin-film solar cells. The desposition condition of CdS:Al was optimised and solar cells with FTO/CdS:Al/CdS/Sb2Se3/Au structure were fabricated. Compared with the device without an N+ layer, the device with the N+ layer exhibited preferable photoelectric response, enlarged depletion-region width, better diode quality and reduced carrier recombination. As a result, improvements of 19% in Voc and 30% in efficiency of the Sb2Se3 thin-film solar cell were realised.

Using Cu-Zn-Sn-O Precursor to Optimize CZTSSe Thin Films Fabricated by Se Doping With CZTS Thin Films.

The copper–zinc–tin oxide (CZTO) precursor was synthesized to avoid sudden volume expansion from CZTO precursor to Cu2ZnSnS4 (CZTS) thin films and smooth CZTSSe thin-film surfaces without pinholes. The CZTO precursor was prepared by coprecipitation and ball milling to form nanoink of CZTO. Based on the CZTO precursor, the CZTS thin film was fabricated and then selenized to make pinhole-free and flat Cu2ZnSn(S,Se)4(CZTSSe) thin films. The results show that the CZTO precursor greatly contributed to elevating the homologous surface characteristics and crystallinity of CZTSSe thin films by controlling selenium temperature, selenium time, and selenium source temperature. Finally, the conversion efficiency of the CZTSSe thin-film solar cell fabricated from the CZTO precursor was 4.11%, with an open-circuit voltage (Voc) of 623 mV, a short circuit current density (Jsc) of 16.02 mA cm−2, and a fill factor (FF) of 41.2%.

Optimized design of silver nanoparticles for broadband and high efficiency light trapping in thin film solar cells

This paper reports a high-efficiency approach to improve the photoelectric-conversion efficiency of thin-film solar cells by plasmonic scattering and local near-field amplification of silver nanoparticles. We employ a three-dimensional (3D) electromagnetic model and use the finite-difference time-domain (FDTD) and rigorously coupled-wave analysis methods to investigate the interaction of light with such a metallic particle. The numerical results show that the absorption and scattering spectra depend upon the properties of the embedded particles and the refractive index of the surrounding material. Strong redshifts and high-order modes are observed in the response spectrum with the increase of the particle size and the refractive index of the surrounding material. With an optimized design having [Formula: see text], [Formula: see text], and [Formula: see text] nm, the performance of cell device is improved over a broad spectral range. Moreover, some of the absorption, in the resonance region, is beyond the Yablonovitch limit. The corresponding light-generated photocurrent is increased from 14.2 mA/cm2 to 18.3 mA/cm2, with a 28.9% enhancement compared with conventional cells with antireflective coatings (ARCs).

Simulating the performance of a highly efficient CuBi2O4-based thin-film solar cell

In this study, copper bismuth oxide (CuBi2O4) absorber-based thin film heterojunction solar cell structure consisting of Al/FTO/CdS/CuBi2O4/Ni has been proposed. The proposed solar cell device structure has been modeled and analyzed by using the solar cell capacitance simulator in one dimension (SCAPS-1D) software program. The performance of the proposed photovoltaic device is evaluated numerically by varying thickness, doping concentrations, defect density, operating temperature, back metal contact work function, series and shunt resistances. The current density–voltage behaviors at dark and under illumination are investigated. To realize the high efficiency CuBi2O4-based solar cell, the thickness, acceptor and donor densities, defect densities of different layers have been optimized. The present work reveals that the power conversion efficiency can be enhanced by increasing the absorber layer thickness. The efficiency of 26.0% with open-circuit voltage of 0.97 V, short-circuit current density of 31.61 mA/cm2, and fill-factor of 84.58% is achieved for the proposed solar cell at the optimum 2.0-μm-thick CuBi2O4 absorber layer. It is suggested that the p-type CuBi2O4 material proposed in the present study can be employed as a promising absorber layer for applications in the low cost and high efficiency thin-film solar cells.

Multidentate anchoring through additive engineering for highly efficient Sb2S3 planar thin film solar cells

Sb2S3 is a promising candidate for the flexible solar cells or the top subcells in tandem solar cells due to its wide-bandgap, less toxic, acceptable cost and progressive power conversion efficiency (PCE). However, the poor quality and high trap states of Sb2S3 films limit the device performance further enhancement. Herein, we adopt a multidentate ionic liquid, tetramethylammonium hexafluorophosphate ([TMA][PF6]) as a novel additive to address this issue. The octahedral [PF6]− contains six different oriented fluorine atoms with the lone pair electrons, which could coordinate with Sb atoms due to the multidentate anchoring. Thus, the high-quality Sb2S3 film with low trap states has been achieved. Moreover, the Fermi level of the Sb2S3 film has been upshifted, thereby showing an effective charge transfer. As a result, all photovoltaic parameters of the optimized Sb2S3 devices are obviously enhanced, boosting the final PCE from 4.43 (control device) to 6.83 %. Our study about the multidentate anchoring is manifested to be an effective method to enhance the Sb2S3 device performance.

Defects and Surface Electrical Property Transformation Induced by Elemental Interdiffusion at the p-n Heterojunction via High-Temperature Annealing.

Heterojunction annealing is widely used to improve the efficiency of kesterite thin-film solar cells. However, the efficiency will decrease when the annealing temperature is high, and the reason why high-temperature postdeposition annealing results in the deterioration of device performance is not well-studied, which restricts the efficiency promotion of kesterite solar cells. This study investigates the effect of high-temperature postdeposition annealing on the p-n heterojunction and, thus, on the performance of the solar cell. The surface potential of the absorber layer inverts, the number of deep-level defects increases, and the CdS/CZTSe interface barrier height increases after high-temperature postdeposition annealing. A combination of different characterization methods reveals that excessive elemental diffusion at the p-n heterojunction during high-temperature postdeposition annealing is the key reason for deterioration of the performance of CZTSe devices. This study discloses the mechanism for the change in device properties with high-temperature postdeposition annealing and will also be helpful for understanding the mechanism of efficiency change as the solar cell keeps working.

Role of intermediate band and carrier mobility in Sn/Fe doped CuAlS2 thin film for solar cell: An ab-initio study

Formation of intermediate band in environmentally stable and wide band gap semiconductor, CuAlS2, have been studied towards potential, low cost and efficient thin film solar cell material. We investigate the effect of sustainable low-cost dopant (Sn and Fe) in CuAlS2 film by means of density functional theory within the modified Becke-Johnson approximation for the calculation of electronic and optical properties. Polar film of CuAlS2 in (001) direction shows lower band gap than the bulk CuAlS2 due to the excess Cu and Al atoms. Doping of Sn and Fe in CuAlS2 form partially filled, isolated intermediate band. Absorption coefficients for Sn and Fe doped films show higher absorption under visible energy region than the pristine bulk and film. Fe and Sn doped films show efficiencies of 34.67 and 35.64%, respectively within spectroscopic limited efficiency. By means of present study, Sn and Fe doping formed intermediate band, improved absorption in visible light and power conversion efficiency. We suggest Sn doped CuAlS2 as the promising material due to higher effective mass ratio of charge carriers, hence lower rate of recombination, indicates improved performance of CuAlS2 based thin film solar cell.

Review on incorporation of alkali elements and their effects in Cu(In,Ga)Se2 solar cells

Cu(In,Ga)Se2 (CIGS) is a promising candidate to replace crystalline silicon solar cells and dominate the photovoltaic market in the future. Alkali elements such as sodium (Na), potassium (K), rubidium (Rb), and Cesium (Cs) are commonly accepted as indispensable parts to boost cell efficiencies of CIGS thin-film solar cells. Therefore, a comprehensive understanding of alkali effects on the electronic and chemical properties of the CIGS layer as well as the underlying mechanisms is of paramount importance for achieving high-performance solar cells. This paper reviews the development process and incorporation pathways of alkalis and then overviews the roles of different alkali elements and their effects on CIGS cells in detail. Furthermore, the unsolved problems and future development prospects are also proposed. Overall, the understanding and development of widely adopted alkali-fluoride post-deposition treatments (PDTs) are still underway, and together with newly updated research, it will likely enable the CIGS technology to make the conversion efficiency closer to its theoretical limit.

Optimization of Ga content gradient in Cu(In,Ga)Se<sub>2</sub> solar cells through machine learning and device simulation

Cu(In,Ga)Se<sub>2</sub> (CIGS) solar cell is a kind of highly efficient thin film solar cell, for which Ga ratio (Ga/(Ga+In), GGI) gradient engineering is an efficient approach to achieving high open circuit voltage under no short circuit current loss. In this work, we firstly evaluate the room and the strategies for improving the device performance of the CIGS solar cells based on the comparison among their theoretical efficiency limits. Then we investigate the different schemes of “V” type GGI gradient and their effects on device performance through machine learning and device simulation. Based on these studies, we optimize the scheme of “V” type GGI gradient and obtain a high efficiency of 26% from device simulation. The carrier kinetics for the effect of modifying GGI gradient on device performance are analyzed. This work provides an approach to optimizing the GGI gradient to obtain highly efficient CIGS solar cells, which is referable for experimental optimization.

Investigation of the effect of annealing conditions on electrodeposited CdTe thin films from non-aqueous bath

We have investigated the effect of annealing conditions onto the cadmium telluride (CdTe) layers obtained using potentiostatic electrodeposition from non-aqueous electrolyte. A conventional three-electrode geometry consisting; working (FTO), counter (Platinum) and reference (Ag/AgCl) electrodes were employed. The samples electrodeposited at − 0.625 V were annealed at 420 °C and cooled down with different procedures. The samples were characterized to study the structural, optical, morphological, compositional and transport properties. Quenched sample is found better as compared to naturally cooled and as-deposited samples. Growth of cubic polycrystalline crystal structure with improved crystallinity of CdTe is revealed from annealed samples. Highly stoichiometric CdTe layers with densely packed globular surface morphology of particle size ~ 2 μm obtained upon annealing the samples is proposed to be suitable for high efficiency thin film solar cells (TFSCs). The micro-structural Raman analysis supports the increased crystallinity and stoichiometric growth of sample after annealing. Highly ohmic behavior with higher carrier concentration and ideality factor measured for quenched samples is reported to be associated to sink in grain boundaries due to grain growth results the densification of sample leads to less defective layers. The results imply that annealing conditions have significant impact on the properties of CdTe samples and the quenched films may be most appropriate as an absorber layer for TFSC applications.

First-principles study of the stability, electronic and optical properties of CdTe under hydrostatic pressure

CdTe is a promising candidate material for stable and high efficiency thin-film solar cells. In the present study, we systematically investigated the effect of hydrostatic pressure on the stability, electronic and optical properties of CdTe based on density functional theory (DFT). From the calculations of phonon dispersions, CdTe is still dynamically stable at high pressure (5.76 GPa). An increase in the band gap is found for CdTe under different pressure conditions, which agrees well with the available experimental results. Moreover, the optical absorption coefficient of CdTe with under pressure is reduced in the visible light region.

Impurity Phases and Optoelectronic Properties of CuSbSe2 Thin Films Prepared by Cosputtering Process for Absorber Layer in Solar Cells

When there is a choice of materials for an application, particular emphasis should be given to the development of those that are low-cost, nontoxic, and Earth-abundant. Chalcostibite CuSbSe2 has gained attention as a potential absorber material for thin-film solar cells, since it exhibits a high absorption coefficient. In this study, CuSbSe2 thin films were deposited by radio frequency magnetron cosputtering with CuSe2 and Sb targets. A series of CuSbxSe2 thin films were prepared with different Sb contents adjusted by sputtering power, followed by rapid thermal annealing. Impurity phases and surface morphology of Cu–Sb–Se systems were directly affected by the Sb sputtering power, with the formation of volatile components. The crystallinity of the CuSbSe2 thin films was also enhanced in the near-stoichiometric system at an Sb sputtering power of 15 W, and considerable degradation in crystallinity occurred with a slight increase over 19 W. Resistivity, carrier mobility, and carrier concentration of the near-stoichiometric thin film were 14.4 Ω-cm, 3.27 cm2/V∙s, and 1.33 × 1017 cm−3, respectively. The optical band gap and absorption coefficient under the same conditions were 1.7 eV and 1.75 × 105 cm−1, which are acceptable for highly efficient thin-film solar cells.

Observation of [VCu1–Ini2+VCu1–] Defect Triplets in Cu-Deficient CuInS2

Copper indium disulfide (CuInS2) is a semiconductor with a direct energy band gap of 1.53 eV—an optimal value for highly efficient thin-film solar cells. But it has reached only ∼11% power conversi...

Hundred-fold reduction in Iron diffusivity in titanium nitride diffusion barrier on steel by microstructure engineering

Titanium nitride (TiN) barrier films can enhance the efficiency of thin-film solar cells on steel by preventing Fe contamination in semiconductor layers. This work uses microstructure engineering to obtain low diffusivity of iron in TiN barrier layers. Three different microstructures were analyzed, each obtained by tuning deposition parameters using pulsed direct current sputtering. We show that metal diffusion in TiN proceeds via two mechanisms – bulk and grain-boundary diffusion. The performance of polycrystalline TiN barrier layers is limited by grain-boundary diffusion. By tuning the microstructure, a remarkably low diffusivity was achieved, only 1.5×10−18cm2s−1 at 700°C, a 100-fold improvement over the state-of-the-art. Activation energy suggests that the diffusion in TiN barrier proceeds via N-vacancies, not grain-boundary defects. For application where electrical insulation is also required, the TiN can be combined with insulating SiNx to form a bilayer barrier, without any loss in performance. The optimized TiN barrier can also be used for stainless steel with a Fe diffusivity of just 9×10−18cm2s−1 at 700°C. However, the TiN barrier on stainless steel suffers from very high chromium diffusion, a previously unknown effect. This suggests that counter to accepted wisdom; stainless steel is not always superior to mild-steel for electronic applications. The work provides quantitative data to aid design of diffusion barriers for electronic devices on steel.

Inter-relationship of the Structural Properties of Quaternary Chalcogenides CuZn2Ga(S/Se)4: A First-Principles Study

Quaternary chalcogenides based on stannite I-II $$_2$$ -III-VI $$_4$$ structure are the best potential candidates to overcome the current generation of solar harvesting materials. First-principles electronic structure simulations were performed on semiconducting CuZn $$_2$$ Ga(S/Se) $$_4$$ (CZGS/Se) to understand the inter-relationship of the structural properties. These structures contain a cubic close packing (ccp) array of S/Se-centered tetrahedrons, coordinated by one Cu, two Zn and one Ga atom occupying one half of the ccp tetrahedral voids. The remarkable variations in the crystal structures are explained by the influence of ionic radii of various atoms. The electronic and optical properties calculated using hybrid functional (Heyd, Scuseria and Ernzerhof, HSE06) show a suitable band gap of 1.59 eV for CZGSe with high optical absorption. The current density and maximum upper limit of theoretical energy conversion efficiency (P(%)) of CZGSe is enhanced when compared to that of CZGS. Our results suggest that the stannite CZGSe structure could be a promising candidate for efficient earth-abundant thin-film solar cell applications.

Multifunctional Enhancement for Highly Stable and Efficient Perovskite Solar Cells

AbstractWith a certified efficiency as high as 25.2%, perovskite has taken the crown as the highest efficiency thin film solar cell material. Unfortunately, serious instability issues must be resolved before perovskite solar cells (PSCs) are commercialized. Aided by theoretical calculation, an appropriate multifunctional molecule, 2,2‐difluoropropanediamide (DFPDA), is selected to ameliorate all the instability issues. Specifically, the carbonyl groups in DFPDA form chemical bonds with Pb2+ and passivate under‐coordinated Pb2+ defects. Consequently, the perovskite crystallization rate is reduced and high‐quality films are produced with fewer defects. The amino groups not only bind with iodide to suppress ion migration but also increase the electron density on the carbonyl groups to further enhance their passivation effect. Furthermore, the fluorine groups in DFPDA form both an effective barrier on the perovskite to improve its moisture stability and a bridge between the perovskite and HTL for effective charge transport. In addition, they show an effective doping effect in the HTL to improve its carrier mobility. With the help of the combined effects of these groups in DFPDA, the PSCs with DFPDA additive achieve a champion efficiency of 22.21% and a substantially improved stability against moisture, heat, and light.

The path towards efficient wide band gap thin-film kesterite solar cells with transparent back contact for viable tandem application

Wide band gap thin-film kesterite solar cell based on non-toxic and earth-abundant materials might be a suitable candidate as a top cell for tandem configuration in combination with crystalline silicon as a bottom solar cell. For this purpose and based on parameters we have extracted from electrical and optical characterization techniques of Cu2ZnGeSe4 absorbers and solar cells, a model has been developed to describe the kesterite top cell efficiency limitations and to investigate the different possible configurations with transparent back contact for four-terminal tandem solar cell application. Furthermore, we have studied the tandem solar cell performance in view of the band gap and the transparency of the kesterite top cell and back contact engineering. Our detailed analysis shows that a kesterite top cell with efficiency > 14%, a band gap in the range of 1.5–1.7 eV and transparency above 80% at the sub-band gaps photons energies are required to achieve a tandem cell with higher efficiency than with a single silicon solar cell.

Some features of selection conditions and manufacturing technology for highly efficient thin-film solar cells based on Si

The main objective of this study is to find the most advanced production technology for semi-voltaic energy converters. The paper presents the results of analysis, production and research of solar cells that have a thin film intersection on Si p- type. The authors also carried out technical analysis of manufacturing and study of heterostructured solar cells of thin layers of crystalline and amorphous silicon. The basic requirements for the production of the most effective light barriers discussed.

Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells

Summary The quaternary chalcogenide halides of group IV and V elements have attracted much attention due to their interesting semiconducting properties as well as a suitable band gap for solar cells. Here, for the first time, we report on solar cells using tin-antimony sulfoiodide (Sn2SbS2I3). Sn2SbS2I3 solar cells were fabricated using a chemical single-step deposition process with a solution containing a SbCl3-thiourea complex and SnI2 with the configuration of TiO2 and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-enzothiadiazole)] as the electron- and hole-transporting layers, respectively. The best-performing cell exhibits a power conversion efficiency of 4.04% under the illumination of standard AM 1.5G conditions (100 mW cm−2). These unencapsulated cells exhibited good stabilities at 80% relative humidity, 85°C in air, and under illumination, respectively. These results provide guidelines for fabrication of lead-free heteroleptic perovskite solar cells by hosting divalent or combinations of monovalent and trivalent metal cations.

Optimization: a proposed pathway to overcome the impasse of low efficiency in CZTS thin-film photovoltaics

The quest to improve the performance of copper zinc tin sulfide (CZTS) thin-film photovoltaics has been increasing recently. This pursuit is driven by the optimal direct bandgap, non-toxic, and abundant constituent elements of CZTS. In this work, a novel CZTS thin-film solar cell with FTO/AZO/CdS/CZTS/MoS2/Mo device structure has been numerically modeled and simulated with SCAPS-1D software. This modeled structure was achieved from a combination of different optimization processes, which involves the window layer, absorber layer, and the back interface of the device. Simulation of this device gave a promising optimized result with a conversion efficiency of 26.19%, a fill factor of 62.07%, a short-circuit current of 27.56 mA cm−2, and an open-circuit voltage of 0.94 V. Further studies from the Mott–Schottky slope showed that the average carrier concentration obtained from the C–V calculations is ~ 5.2 × 1016 cm−3. The simulation processes provide an essential guideline for the fabrication of highly efficient CZTS thin-film solar cell.