Fabrication Of Thin Film Solar Cells Research Articles

Self-assembled growth of quasi-vertically oriented Sb2S3 thin films for substrate structured solar cells

Antimony sulfide (Sb2S3) is an appealing one-dimensional light-harvesting material for thin-film solar cells due to the high absorption coefficient, suitable bandgap and abundance of constituent elements. The orientation of the Sb2S3 thin film is considered as one of the most important factors affecting the performance of the device. According to the minimum energy principle, Sb2S3 is prone to grow parallel to the substrate along the [hk0] orientation which is harmful to the device performance. On the other hand, [hk1]-oriented films are much more beneficial but additional processes such as annealing are often required. In this work, stoichiometric Sb2S3 thin films consist of compact, highly [hk1]-oriented grains have been prepared via a self-assembled growth by magnetron sputtering and post-sulfurization. After carefully optimized the preparation process, a champion device (2.89% power conversion efficiency) was obtained with an open-circuit voltage of 696 mV and a short-circuit current density of 12.48 mA/cm2 under AM 1.5G solar radiation. Interestingly, the high open-circuit voltage of our device is already comparable to the state-of-the-art Sb2S3 solar cells. This work demonstrates a great potential of the sputtering and post-sulfurization method in fabrication of high-efficiency substrate Sb2S3 thin-film solar cells.

Towards a promising systematic approach to the synthesis of CZTS solar cells

This study aims to enhance the CZTS device's overall efficiency, the key research area has been identified in this study is to explore the effects of a novel, low-cost, and simplified, deposition method to improve the optoelectronic properties of the buffer layer in the fabrication of CZTS thin film solar cells. Herein, an effective way of addressing this challenge is through adjusting the absorbers' structure by the concept of doping, sensitized CdS thin film by the bi-functional linker, and an environmentally friendly catalytic green agent. The Linker Assisted and Chemical Bath Deposition (LA-CBD) method was introduced as an innovative and effective hybrid sensitization approach. In the one-step synthesis process, Salvia dye, Ag, and 3-Mercaptopropionic acid (MPA) were used. Generally, the results for all samples displayed varying bandgap as achieved between (2.21–2.46) eV, hexagonal structure with considerably decreased strain level, broader grain size, and dramatically enhanced crystalline property. Hence, the rudimentary CdS/CZTS solar cell devices were fabricated for the application of these novel CdS films. Preliminary CZTS thin film solar cell fabrication results in the highest conversion efficiency of 0.266% obtained CdS + Salvia dye, indicating the potential use of the CdS films as a buffer layer for CZTS photovoltaic devices.

Antimony Selenide Solar Cells Fabricated by Hybrid Reactive Magnetron Sputtering.

The fabrication of Sb2Se3 thin-film solar cells deposited by a pulsed hybrid reactive magnetron sputtering (PHRMS) was proposed and examined for different growth conditions. The influence of growth temperature and Se pulse period were studied in terms of morphology, crystal structure, and composition. The Sb2Se3 growth showed to be dependent on the growth temperature, with a larger crystal size for growth at 270 °C. By controlling the Se pulse period, the crystal structure and crystal size could be modified as a function of the supplied Se amount. The solar cell performance for Sb2Se3 absorbers deposited at various temperatures, Se pulse periods and thicknesses were assessed through current-voltage characteristics. A power conversion efficiency (PCE) of 3.7% was achieved for a Sb2Se3 solar cell with 900 nm thickness, Sb2Se3 deposited at 270 °C and Se pulses with 0.1 s duration and period of 0.5 s. Finally, annealing the complete solar cell at 100 °C led to a further improvement of the Voc, leading to a PCE of 3.8%, slightly higher than the best reported Sb2Se3 solar cell prepared by sputtering without post-selenization.

Co-Electrodeposition of Metallic Precursors for Cd-Doped Cu2ZnSnS4 (CZCTS) Kesterite Absorber for Photoelectrochemical Water Splitting

Electrodeposition is widely studied in the fabrication of semiconductors for solar application, because of the low cost and easy scalability of this technique. For instance, in the last decades large effort has been dedicated to the electrodeposition of Cu2ZnSnS4 (CZTS) through different approaches, including either direct co-electrodeposition of the sulfide, the deposition of metallic alloy precursors or by stacked elemental layer, depositing Cu, Zn and Sn in sequence, then converting it into kesterite with thermal treatment in sulfur atmosphere.1–4 While being a promising alternative to CIGS (CuInGaS2), thanks to the non-toxicity and higher abundance of its constituting elements, CZTS absorbers still encounter some difficulties to their integration of high-performance solar devices. In fact, the electronic and optical properties of the material are affected by the narrow stoichiometric window acceptable for kesterite formation, inducing the segregation of secondary phases, along with the formation of lattice defects that act as recombination sites.5 A reported strategy to suppress the latter limitation is to introduce doping elements such as Ag6 and Cd7,8, partially substituting metallic atoms in the semiconductor, Cu and Zn respectively. The larger atomic radii of these elements can prevent the formation of antisite defects such as CuZn, largely increasing the semiconductor performance7. Here we propose a synthesis route of CZCTS through the co-electrodeposition of a thin film Cu-Sn-Zn-Cd alloy followed by sulfurization treatment. The deposition on SLG/Mo substrate is achieved with a sulfate-based electrolyte with citrate complexing agents and performed in three-electrode potentiostatic conditions. Proper bath formulation is designed to obtain a desirable Zn-rich, Cu-poor composition, varying the degree of Zn substitution with Cd. An alternative 2-step deposition of CuZnSn/Cd stacked precursor is also investigated, as an attempt to compensate the effect of the low H+ adsorption energy of cadmium leading to the formation of blisters in the quaternary alloy. Sulfurized samples characterization shows the formation of good quality of kesterite CZCTS, in spite of the segregation of secondary phases on the surface. Cd doping of CZTS is observed through the characteristic shift of the main kesterite XRD peak (112) and an increase of the average size of grains. The photocurrent of finalized photocathodes with structure SLG/Mo/CZCTS/CdS/Pt is measured under 10 mW/cm2 AM 1.5 radiation reporting an improvement with respect to the undoped analogue, increasing the current density at 0 V vs RHE from -5.73 to -7.18 mA/cm2 in the best case.Bibliography Colombara, D. et al. Electrodeposition of kesterite thin films for photovoltaic applications: Quo vadis? Phys. Status Solidi Appl. Mater. Sci. 212, 88–102 (2015).Ge, J. & Yan, Y. Controllable Multinary Alloy Electrodeposition for Thin-Film Solar Cell Fabrication: A Case Study of Kesterite Cu2ZnSnS4. iScience 1, 55–71 (2018).Clauwaert, K., Binnemans, K., Matthijs, E. & Fransaer, J. Electrochemical studies of the electrodeposition of copper-zinc-tin alloys from pyrophosphate electrolytes followed by selenization for CZTSe photovoltaic cells. Electrochim. Acta 188, 344–355 (2016).Jiang, F. et al. Pt/In2S3/CdS/Cu2ZnSnS4 Thin Film as an Efficient and Stable Photocathode for Water Reduction under Sunlight Radiation. J. Am. Chem. Soc. 137, 13691–13697 (2015).Polizzotti, A., Repins, I. L., Noufi, R., Wei, S. H. & Mitzi, D. B. The state and future prospects of kesterite photovoltaics. Energy Environ. Sci. 6, 3171–3182 (2013).Yuan, Z. K. et al. Engineering Solar Cell Absorbers by Exploring the Band Alignment and Defect Disparity: The Case of Cu- and Ag-Based Kesterite Compounds. Adv. Funct. Mater. 25, 6733–6743 (2015).Tay, Y. F. et al. Solution-Processed Cd-Substituted CZTS Photocathode for Efficient Solar Hydrogen Evolution from Neutral Water. Joule 2, 537–548 (2018).Su, Z. et al. Device Postannealing Enabling over 12% Efficient Solution-Processed Cu2ZnSnS4 Solar Cells with Cd2+ Substitution. Adv. Mater. 32, 1–12 (2020).

A discrete boundedness-by-entropy method for finite-volume approximations of cross-diffusion systems

Abstract An implicit Euler finite-volume scheme for general cross-diffusion systems with volume-filling constraints is proposed and analyzed. The diffusion matrix may be nonsymmetric and not positive semidefinite, but the diffusion system is assumed to possess a formal gradient-flow structure that yields $L^\infty $ bounds on the continuous level. Examples include the Maxwell–Stefan systems for gas mixtures, tumor-growth models and systems for the fabrication of thin-film solar cells. The proposed numerical scheme preserves the structure of the continuous equations, namely the entropy dissipation inequality as well as the non-negativity of the concentrations and the volume-filling constraints. The discrete entropy structure is a consequence of a new vector-valued discrete chain rule. The existence of discrete solutions, their positivity, and the convergence of the scheme is proved. The numerical scheme is implemented for a one-dimensional Maxwell–Stefan model and a two-dimensional thin-film solar cell system. It is illustrated that the convergence rate in space is of order two and the discrete relative entropy decays exponentially.

Engineering of CIGS nanoparticle inks for colloidal stability, uniform film formation and application as HTL for perovskite solar cells

In this work, synthesis of CuIn0.75Ga0.25S2 (CIGS) nanoparticles, the formation of stable dispersion, deposition of high-quality films and, fabrication of thin-film Perovskite solar cells are reported. The stability of nanoparticle ink is crucial in the formation of device-quality films. The chalcogenide-based materials are widely used in thin-film solar cells; in particular, Cu(In,Ga)S2 are used as an absorber and hole transporting layer. In the present study, the nanoparticles of about 20 nm size and bandgap of 1.5 eV are synthesized using a heat-up method. A variety of solvents are used as dispersing media and the stability of the inks is evaluated by precise optical monitoring. We observe a clear dependence of ink stability to the polarity index of the solvent, where the best stability occurs at a polarity index of about 0.26–0.36, corresponding to a range of solvents including chloroform. The thin films that are spin-coated using CIGS chloroform ink show large cracks, presumably due to the high vapor pressure of chloroform and evaporation-induced stress in the film. We resolve this problem through low-temperature deposition, which resulted in highly uniform pin-hole and crack-free films. Finally, the optimum deposition condition is used to fabricate perovskite solar cells having about 16.5% efficiency with CIGS as a hole transport layer.

Chemical and Electrical Instability of MgxZn1−xO in CdTe Thin Film Solar Cell

Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O (MZO) is a promising window material for high-efficiency CdTe thin film solar cell fabrication. However, the performance of MZO-based CdTe solar cell exhibits high sensitivity to the heat treatment of MZO during device fabrication process. In this article, the chemical, microstructural and electrical instability of MZO films and their effect on device performance of CdTe thin film solar cell was studied. It is found that during the high-temperature vacuum treatment (400°C-600°C), the atomic element losses in the MZO films led to high oxygen-vacancy concentration and formation of an Mg-rich surface layer. The high-temperature treated MZO films exhibited rough surface morphology, high electronic conductivity, and low electron affinity. The rough MZO surface induced formation of trap states with high concentration in the CdTe absorber and decreased open-circuit voltage for the solar cell. The MZO conductivity and the surface electron affinity affect the carrier transport in the solar cells. This work demonstrates that the heat treatment process of the MZO window layer significantly affects the performance and reproducibility of CdTe solar cell fabrication.

An unconventional blade coating for low-cost fabrication of PCDTBT: PC70BM polymer and CH3NH3PbIxCl3-x perovskite solar cells

A low-cost and unconventional blade coating technique, called convective deposition, has been introduced for PCDTBT:PC70BM polymer and CH3NH3PbIxCl3-x perovskite solar cell fabrication. With the new technique, only 10–20 microliter droplets per one square inch substrate were used to deposit hole transporting material, as well as photoactive and electron transporting materials, sequentially to create a p-i-n structure solar cell. Thin film deposition and solar cell fabrication from the standard spin coating and the convective deposition were compared. Smaller and better distribution of PC70BM domain in the PCDTBT:PC70BM film was observed in the film prepared by the convective deposition. Unlike the conventional doctor-blade coating or the spin coating, the film thickness can simply be adjusted by the convective deposition speed. The highest averaged power conversion efficiency (PCE) of 6.34% was obtained from the polymer solar cell prepared by the convective deposition at the coating speed of 750 μm/s compared to 5.60% PCE from the spin coating at the speed of 2500 rpm. For perovskite solar cell, a heating stage was used during the convective deposition of perovskite ink, 10.61% PCE was achieved with the stage temperature of 70 °C and the 2500 μm/s deposition speed. Layer-by-layer deposition with the convective deposition used in this study offers benefits over the standard spin coating by reducing amount of material consumption in the fabrication process and being suitable for low-cost fabrication of other solution-based optoelectronic devices.

Fabrication of monoclinic-Cu2SnS3 thin-film solar cell and its photovoltaic device performance

Abstract Single-phase monoclinic Cu2SnS3 (M-CTS) thin films have a good tendency to obtain high conversion efficiency in photovoltaic devices. In this study, single-phase monoclinic Cu2SnS3 (M-CTS) thin films are prepared by a combination of sputtering and sulfurization processes. The M-CTS device shows a power conversion efficiency of 0.64% with an open-circuit voltage of 0.184 V, a short circuit current of 12.63 mA/cm2, and fill factor of 27.36. The required single-phase structure of M-CTS is confirmed by the X-ray diffraction and Raman spectroscopy. Quantitative analysis by a Rietveld refinement of the XRD patterns of CTS films reveal a monoclinic crystal structure. The M-CTS thin-film shows a compact morphology, direct optical bandgap of 0.95 eV, a thickness of ~1 μm, and electrical properties, including resistivity of 1.50 Ω-cm, hole mobility of 5.02 cm2/V, and carrier concentration of 8.30 × 1017 cm−3 with p-type conductivity. Based on these advantages, further studies are expected to drastically enhance the efficiency of M-CTS solar devices.

Silver and copper nanowire films as cost-effective and robust transparent electrode in energy harvesting through photovoltaic: A review

Presently, there is a high demand for cost-effective, solution-processed technology for fabrication of thin-film solar cell to compete with the well-stabilised Si-solar cell at industrial scale. In thin-film solar cell, the active layers such as absorber and interfacial layer can be deposited by a cost-effective chemical route but the transparent electrode, which is generally ITO, is deposited using vacuum-based expensive technology. To minimize the overall fabrication cost of thin-film solar cell, in addition to absorber and interfacial layers, the deposition of solution-processed transparent electrode is also required. To replace ITO, researcher have given major efforts to apply solution-processed Ag and Cu nanowire networks as transparent electrode owing to their excellent conductivity and transmittance. In this review, we present recent advances in the application of Ag and Cu nanowire-based transparent electrode in photovoltaic. The inherent issues pertaining to application of nanowire-based transparent electrode in fabrication of organic and perovskite solar cells is addressed.

Fabrication of Thin-Film Solar Cells Based on CdTe Films and Investigation of Their Photoelectrical Properties

This study presents the results of investigating thin-film CdS/CdTe-based solar cells obtained on glass substrates with In2O3(Sn) and SnO2 frontal electrodes. On the surface of frontal electrodes (In2O3(Sn)/SnO2), 100-nm thick cadmium sulfide films were deposited by vacuum thermal evaporation at a substrate temperature of 200°C, then application of 4–5-μm thick cadmium telluride films by chemical molecular beam deposition at a substrate temperature of 600°C. The obtained heterosystems were subjected to “chloride” treatment, which is a standard technological operation for the fabrication of efficient solar cells based on CdS/CdTe. Photoelectrical characteristics of the resulting solar cells were studied. An increase in the efficiency of thin-film solar cells after heat treatment was shown.

Toward Phase Stability: Dion–Jacobson Layered Perovskite for Solar Cells

Three-dimensional halide-based perovskites have emerged as promising semiconducting light harvesters for thin-film solar cell fabrication; however, their intrinsic instability under humidity restri...

CZTSSe solar cell efficiency improvement using a new band-gap grading model in absorber layer

Earth abundant copper–zinc–tin–chalcogenide is an attractive class of materials for the fabrication of high efficiency, low cost, and sustainable thin-film solar cells. A CZTSSe solar cell was modeled and the effects of absorber layer band-gap grading were investigated. Regarding the tunable bandgap of kesterite absorber layers which is between 0.95 eV for CZTSe and 1.5 eV for CZTS, several grading models were simulated in SCAPS. First, using a set of comprehensive absorption data for CZTS and CZTSe, the basic bandgap was selected to be 1.15 eV due to experimental aspects, and then, five grading models namely back/front linear, back/front exponential, and inside graded were explored. The investigation of simulation results showed that the recombination rate improvement in back and front regions along with current density enhancement is achievable by these graded band-gap profiles. Finally, the modified inside graded model was reached to a power conversion efficiency of 15.6% which leaded to a considerable output performance.

High Quality CdS/CdTe P-N Junction Diode With a Noncontinuous Resistive SnO2 Buffer Layer

In order to reduce light absorption of the n-type CdS window layer in high efficiency CdTe thin film solar cells, the window layer should be as thin as possible but enough thickness should be left to keep function of the p-n junction. However, many random shunting/shorting micropaths are unavoidably formed at the CdS/CdTe interface due to the CdS consumption up by the reaction/interdiffusion, or due to a noncontinuous coverage of CdS on transparent-conducting-oxide (TCO) thin films. These shunting/shorting paths are the main cause for the low open-circuit voltage and low efficiency of CdTe thin film solar cells. In this study, we propose to employ a noncontinuous highly resistive tin oxide (SnO2) layer between the TCO and the CdS window layer as an electronic shunting blocking layer. The experimental results demonstrated that the insertion of a noncontinuous SnO 2, which had a thickness of less than 10 nm, led to an enhancement in efficiency by 20% and an increase in open-circuit voltage ( $V_{{\rm{oc}}}$ ) by 14% compared to the one without SnO2. This study demonstrated an important design strategy for thin film solar cell fabrication to effectively reduce microshunting/shorting paths and to improve fabrication reproducibility of devices as well.

Chemistry and Dynamics of Ge in Kesterite: Toward Band-Gap-Graded Absorbers

The selenization of metallic Cu–Zn–Sn–Ge precursors is a promising route for the fabrication of low-cost and efficient kesterite thin-film solar cells. Nowadays, efficiencies of kesterite solar cells are still below 13%. For Cu(In,Ga)Se2 solar cells, the formation of compositional gradients along the depth of the absorber layer has been demonstrated to be a key requirement for producing thin-film solar cells with conversion efficiencies above the 22% level. No clear understanding has been reached so far about how to produce these gradients in an efficient manner for kesterite compounds, but among the possible candidates, Ge arises as one of the most promising ones. In the present work, we evaluate the potential of incorporating Ge in Cu2ZnSnSe4 to produce compositional gradients in kesterites. Synchrotron-based in situ energy-dispersive X-ray diffraction and X-ray fluorescence have been used to study the selenization of Cu–Zn–Sn–Ge metallic precursors. We propose a reaction mechanism for the incorporation...

Optical properties of thermally evaporated In2S3 thin films measured using photoacoustic spectroscopy

In2S3 is a III-VI group semiconductor with n-type conductivity and a wide band gap energy, which can be suitable as a buffer layer alternative to CdS in thin film solar cell fabrication. In the present study, In2S3 thin films were grown on glass substrates by the thermal evaporation method at a constant substrate temperature of 200°C. The deposited layers were post annealed in vacuum in the temperature range of 200–300°C for 1h. The grazing incident X-ray diffraction and scanning electron microscopy studies revealed polycrystalline nature of the layers with a good surface morphology. The optical properties of these annealed layers were investigated by using photoacoustic spectroscopy and independently by using conventional optical transmission spectroscopy. The photoacoustic spectra of In2S3 films showed a sharp fall in the photoacoustic signal at photon energies that increased from 1.95 to 2.74eV with increasing annealing temperature, which corresponds to the band gap energy of corresponding films. The band gap energy and the refractive index values calculated by using photoacoustic spectra are in good agreement with that determined from transmission spectra.

CdTe thin film solar cell with NiO as a back contact buffer layer

In this work, p-type NiO thin film was applied as a buffer layer in the back contact for CdTe thin film solar cell fabrication. The NiO layers were prepared by electron beam evaporation. By optimizing NiO layer thickness in the back contact a CdTe solar cell with an efficiency of 12.17% and an open-circuit voltage Voc of 790mV has been fabricated. X-ray photoelectron spectroscopy study showed that NiO has a staggered band alignment with CdTe. Such an electronic band structure alignment allows smooth hole transport from CdTe to NiO and at the same time NiO acts as a surface field layer to reduce electron recombination at the back contact interface, thus leading to improved Voc. This study also demonstrates that by employing NiO as a buffer layer, much less Cu was needed for the CdTe solar cell fabrication and the cell device stability had been significantly enhanced compared to the CdTe solar cell with a conventional Cu/Au bimetal layer as the back contact.

Room temperature deposition of highly crystalline Cu-Zn-S thin films for solar cell applications using SILAR method

Cu-Zn-S having inexpensive, non-toxic, and earth-abundant constituent elements, combined with suitable optical and electrical properties is a promising candidate as an absorber material for thin film solar cell fabrication. We report the deposition of Cu-Zn-S thin films using Successive Ionic Layer Adsorption and Reaction (SILAR) method under room temperature and atmospheric conditions. Cu-Zn-S thin films are deposited over glass substrates with different Cu/(Cu+Zn) ratio in the precursor solution to investigate the band gap tunability. The as-deposited Cu-Zn-S films are characterized for determining their structural, compositional, morphological, optical and electrical properties. Also studied the stability of electrical properties for a period of six months after the deposition. All the films exhibited p-type conductivity and a relatively high absorption coefficient value between 104 to 105 cm−1 in the visible and near-IR spectral range. We observed that, under the Zn-rich growth conditions, the films formed are having a double band gap structure with lower band gap values in the range 1.6–1.7 eV, making them a suitable absorber material for solar cell fabrication. Under the Cu-rich growth conditions, band gap values reached 2.4–2.6 eV making them a suitable buffer/window layer in solar cell application. Notably, films with Cu/(Cu+Zn) ratio 0.8 showed an optical transparency of 40–70% in the visible spectrum along with an electrical conductivity of 2900 S cm−1, which is much higher than the other reported p-type transparent conducting materials.

Fabrication of Cu2SnS3 thin-film solar cells with oxide precursor by pulsed laser deposition

In this paper, Cu2SnS3 (CTS) thin film is fabricated through sulfurization of oxide precursor which is deposited by pulsed laser deposition with a mixed CuO/SnO2 target. XRD and Raman analyses indicate a pure monoclinic Cu2SnS3 phase has been obtained by sulfurization at temperature from 500 to 600 °C. A compact and smooth film with polycrystalline structure is observed through SEM result. In addition, the CTS films show excellent absorbance with the band gap around 0.91 eV estimated by UV–Vis, which is suitable for the absorption layer of solar cells. Final devices were fabricated with a SLG/Mo/CTS/CdS/i-ZnO/AZO/Al structure. Device performance is improved with the temperature increasing. The best efficiency of CTS-based solar cells is 0.69% with an open-circuit voltage of 144 mV and a short-circuit current density of 18.30 mA/cm−2.

Laser scribing of CIGS thin-film solar cell on flexible substrate

Laser scribing technology has been actively developed for thin-film solar cell fabrication taking a number of advantages over mechanical scribing. Its non-contact processing nature enables reliable and precise scribing processes. In particular, it is almost unavoidable to use laser scribing method for fabricating high-quality flexible thin-film solar cells. Despite the fundamental merits that laser scribing can offer, still a number of challenges should be addressed in order to replace the mechanical counterpart for wider range of thin-film solar cells. In this study, we explore optimal laser scribing conditions for copper–indium–gallium–selenide (CIGS) thin-film solar cells, especially based on flexible polyimide (PI) substrate in close comparison with that based on soda-lime glass substrate. Picosecond-pulsed laser of repetition rate up to 100 kHz and wavelength of 532 nm (~12 ps temporal pulse width) was mainly tested, and scribing speed in the range of 0.01–1 m/s was examined with a few different laser focal spot diameters (27, 34, and 62 μm). Main focus of this study is in understanding distinct laser scribing mechanisms for flexible substrate configurations, thereby finding out intrinsic optimal processing parameters. One of the most critical requirements is to prevent possible damage or deformation of underlying thin-film layer(s) or PI substrate. Effect of microstructures of thin films (in particular, Mo and CIGS) on the scribing behavior was also examined. In order to further improve the performance of the scribing process and reduce the laser power budget as well, mild gas injection scheme was tested.