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Influence of RbF post deposition treatment on heterojunction and grain boundaries in high efficient (21.1%) Cu(In,Ga)Se2 solar cells
摘要： Post deposition treatments (PDT) by alkali fluorides applied to chalcopyrite-based absorbers have produced record efficiencies in thin-film solar devices in the past few years and recently the efficiency of 22.6 % was achieved with Cu(In,Ga)Se2 (CIGS) using rubidium fluoride (RbF) PDT. However, the effects of RbF-PDT towards changes in its interfacial and grain boundary (GB) properties are still not fully understood. In this work, cells with efficiency higher than 21% are investigated by combination of atom probe tomography (APT) and transmission electron microscopy (TEM) to show how changes in GB and interface chemistry may facilitate high efficiencies. APT studies, carried out at the interface between CIGS absorber and solution-grown CdS buffer layer, show In enrichment and Cu depletion along with traces of Rb. Our APT studies reveal higher amounts of Rb (1.5 at. %) and lower amounts of Na and K (<0.5 at. %) at GBs as compared with previous studies (on non-PDT samples) thus indicating substitution of Na and K by Rb. However, concentration of all alkali elements inside the grain bulk is below detection limit of APT. The concentration of Rb at the GBs in CIGS is measured depth-dependent using both APT and TEM, which consistently shows the increase in Rb towards the Mo back contact. In addition, a pronounced Cu depletion is observed at the GBs which might enhance hole-barrier properties of the GBs, thus improving charge carrier collection and hence the overall efficiency of the device. Thus, understanding effects of RbF-PDT at the atomic scale provides new insights concerning the further improvement of CIGS absorber and interfaces.
关键词： Cu(In,Ga)Se2,Thin-film solar cell,heterojunction,atom probe tomography,post deposition treatments,transmission electron microscopy
更新于2025-11-21 11:20:48
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Cu(In,Ga)Se2 monograin powders with different Ga content for solar cells
摘要： Monograin layer (MGL) solar cell technology based on CuIn1-xGaxSe2 (CIGSe) monograin powder crystals is a promising approach for the future low-cost production of flexible solar panels. In this study, CuIn1-xGaxSe2 monograin powders (0 ≤ x ≤ 1) were prepared from binary compounds in the liquid phase of potassium iodide as flux material in evacuated quartz ampoules at 720 °C. The crystal structure and the lattice parameters of the CIGSe monograin powder crystals were determined by using X-ray diffraction analysis. A linear decrease of the lattice parameters with increasing Ga concentration was detected. The photoluminescence (PL) spectra of the CIGSe crystals were dominated by the edge emission band that shifted towards higher energies with increasing Ga content. Moreover, additional deep PL band (below 1.0 eV) appeared for Ga contents above x = 0.21 showing higher relative intensity with increasing Ga content. The effective bandgap energy of the CIGSe monograin powder materials ranged from 1.0 eV to 1.68 eV as the [Ga]/([In] + [Ga]) ratio increased from 0 to 1.0. An efficiency of 12.8% (active area) was obtained with the MGL solar cell based on CuIn1-xGaxSe2 monograin powder with Ga content of x = 0.21.
关键词： Cu(In,Ga)Se2,Solar cell,Crystalline powder,Crystal growth
更新于2025-11-21 10:59:37
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Device simulation of Cu(In,Ga)Se2 solar cells by means of voltage dependent admittance spectroscopy
摘要： The simulation of solar cell devices is important for the understanding of defect physics and loss mechanisms in real solar cells. On the other hand, voltage dependent admittance spectroscopy delivers essential information for establishing a baseline simulation model of Cu(In,Ga)Se2 (CIGSe) solar cells. Here we give an explanation for the weak temperature dependence of the N1-signal, the latter being not compatible with a bulk defect or with a simple hole barrier at the Mo back contact. Furthermore, we find a Ed,IF – EV ≈ 0.3 eV deep recombination-active acceptor state at the absorber/buffer interface made of air-light exposed CIGSe absorbers. This gives us the ability to explain the reduction of power conversion efficiency of solar cells made from air-light exposed absorbers. From the voltage dependent capacitance step of this interface defect we can deduce the formerly unknown position of the Fermi level at the hetero junction in equilibrium which is close to mid-gap. Simulation of dark J-V curves allows a refinement of the parameter of this absorber/buffer interface defect, resulting in a defect density of Nd,IF ≈ 3.5·1011 cm-2 as well as capture cross sections of σn ≈ 4·10-16 cm2 for electrons and σp ≈ 3·10-11 cm2 for holes.
关键词： device simulation,Cu(In,Ga)Se2,admittance spectroscopy,defect physics,solar cells
更新于2025-11-14 17:28:48
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Impact of KF-post deposition treatment on Cu(In,Ga)Se2 surface and Cu(In,Ga)Se2/CdS interface sulfurization
摘要： Partial sulfurization of Cu(In,Ga)Se2 (CIGSe) absorbers contributes to enhance photovoltaic performance of chalcopyrite based solar cells. Alternatively, KF post-deposition treatment (KF-PDT) performed under Se atmosphere has recently been used to improve the efficiency of CIGSe thin film based solar cells. In this work, we study the potential sulfurization of KF-treated CIGSe during the chemical bath deposition of the CdS buffer layer. Therefore, buried interfaces between KF-PDT CIGSe under Se or S atmosphere and CdS are investigated with the help of non-destructive and depth sensitive X-ray emission spectroscopy. No CIGSe sulfurization is detected at the absorber/CdS interface when KF treatment is performed under selenium atmosphere. In contrast, when KF treatment is done under sulfur atmosphere, partial sulfurization of CIGSe is detected at the CIGSe/CdS interface. We show through X-ray photoemission spectroscopy that the CIGSe sulfurization occurs during the KF-PDT performed under sulfur atmosphere. We also demonstrate that alkali favors greatly CIGSe surface sulfurization when the chalchopyrite is exposed to sulfur atmosphere.
关键词： Cu(In,Ga)Se2,XES,KF-PDT,XPS,Interface,Sulfurization
更新于2025-09-23 15:23:52
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Voltage-Induced Charge Redistribution in Cu(In,Ga)Se <sub/>2</sub> Devices Studied With High-Speed Capacitance–Voltage Profiling
摘要： Devices made from Cu(In,Ga)Se2 (CIGS) solar cell material have been evaluated with high-speed capacitance–voltage pro?ling after stepwise voltage changes. The changes primarily affect near-interface charge at deep acceptors within the CIGS absorber layer and generate temperature-dependent capacitance changes observed in deep-level transient spectroscopy measurements. SCAPS device modeling indicates that the deep acceptor concentration is up to the two orders of magnitude higher than the shallow doping level. High deep acceptor concentrations are found in all materials studied here. The large deep defect levels are high enough to limit minority carrier lifetime and cell ef?ciency.
关键词： CuInx Ga1 ?x Se2 (CIGS),capacitance methods,solar cells
更新于2025-09-23 15:23:52
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Control of Structural and Electrical Properties of Indium Tin Oxide (ITO)/Cu(In,Ga)Se <sub/>2</sub> Interface for Transparent Back-Contact Applications
摘要： Development of transparent-conducting oxide (TCO) back contact for Cu(In,Ga)Se2 (CIGS) absorber is crucial for bifacial CIGS photovoltaics. However, GaOx formation at the TCO/CIGS interface has hampered the photocarrier extraction. Here, by controlling the Na doping scheme, we show that the hole transporting properties at the indium?tin oxide (ITO)/CIGS back contact can be substantially improved, regardless of the GaOx formation. Na incorporation from the glass substrate during the GaOx forming phase created defective states at the interface, which allowed efficient hole extraction from CIGS, while post Na treatment after GaOx formation did not play such a role. Furthermore, we discovered that an almost GaOx-free interface could be made by reducing the underlying ITO film thickness, which revealed that ITO/CIGS junction is inherently Schottky. In the GaOx-free condition, post-Na treatment could eliminate the Schottky barrier and create ohmic junction due to generation of conducting paths at the interface, which is supported by our photoluminescence analysis.
关键词： Schottky barrier,indium-tin oxide,photovoltaics,Na doping,Ga)Se2,ohmic contact,GaOx,transparent-conducting oxide,Cu(In
更新于2025-09-23 15:22:29
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Post Deposition Treatments of (Ag,Cu)(In,Ga)Se <sub/>2</sub> Thin Films for Solar Cells
摘要： Different alkali alternatives for post-deposition of ACIGS were tested, both conventional fluoride salts and in the form of metals. XPS analysis of surfaces treated with K or KF as well as Rb or RbF have been performed, before (only for K and Rb) and after an ammonia etch. In addition to a strong suppression of Cu and Ag near the surface, we observe a difference in the re-distribution of Ga in the surface region after the etch depending on pdt element. Our results are consistent with the formation of K-In-Se and Rb-In-Se compounds for both metal alkalis and alkali fluorides. We find a similar beneficial effect on cell performance for the best cells with the metals as with the fluoride salts.
关键词： KF,Rb,RbF,ACIGS,K,alkali post deposition treatment,(Ag,Cu)(In,Ga)Se2
更新于2025-09-23 15:21:01
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Improvement of Cu(In,Ga)Se <sub/>2</sub> solar cell performance by thiourea treatment
摘要： We investigated the effects of a thiourea treatment performed to the absorber of Cu(In,Ga)Se2 (CIGS) solar cells. The thiourea treatment successfully improved the open-circuit voltage, fill factor, and conversion efficiency of the solar cells. Reduced ideality factor and reverse saturation current density demonstrated that the suppression of carrier recombination contributed to the improvement in solar cell performance. Increased intensity in cross-sectional electron-beam-induced current measurements confirmed the improved film quality with the thiourea treatment. Additionally, an enhanced carrier density observed with the treatment suggests the passivation of donor-type defects. These results indicate that the thiourea treatment is promising to improve the absorber quality and enhance the performance of CIGS solar cells.
关键词： thiourea treatment,solar cell,Cu(In,Ga)Se2,carrier recombination,film quality
更新于2025-09-23 15:21:01
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Challenges and opportunities for efficiency boost of next generation Cu(In,Ga)Se <sub/>2</sub> solar cells: prospect for a paradigm shift
摘要： Cu(In,Ga)Se2 photovoltaic technology has notably progressed over the past years. Power conversion efficiencies above 23% were reached in spite of the absorber polycrystalline nature. Although efficiencies are still far from the practical limits, the material quality is approaching that of III-V compounds that yield the most efficient solar cells. High carrier lifetime, low open circuit voltage deficit and external radiative efficiency in single-digit percentage range, suggest the next efficiency boost may arise from the implementation of alternative device architectures. In this perspective paper, we describe the current challenges and pathways to enhance the power conversion efficiency of Cu(In,Ga)Se2 solar cells. Specifically, we suggest the use of non-graded absorbers, integration of charge selective contacts and maximization of photon recycling. We examine these concepts by a semi-empirical device modelling approach, and show that these strategies can lead to efficiencies of 29% under the AM1.5 global spectrum. An analysis whether or not current state-of-the-art Cu(In,Ga)Se2 solar cells already benefit from photon recycling is also presented.
关键词： Cu(In,Ga)Se2,charge selective contacts,photon recycling,power conversion efficiency,solar cells
更新于2025-09-23 15:21:01
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Characterization of Lattice Parameters Gradient of Cu(In1-xGax)Se2 Absorbing Layer in Thin-Film Solar Cell by Glancing Incidence X-Ray Diffraction Technique
摘要： In or Ga gradients in the Cu(In1-xGax)Se2 (CIGS) absorbing layer lead to change the lattice parameters of the absorbing layer, giving rise to the bandgap grading in the absorbing layer which is directly associated with the degree of absorbing ability of the CIGS solar cell. We tried to characterize the depth profile of the lattice parameters of the CIGS absorbing layer using a glancing incidence X-ray diffraction (GIXRD) technique, and then allows to determine the In or Ga gradients in the CIGS absorbing layer, and to investigate the bandgap grading of the CIGS absorbing layer. When the glancing incident angle increased from 0.50 to 5.00°, the a and c lattice parameters of the CIGS absorbing layer gradually decreased from 5.7776(3) to 5.6905(2) ?, and 11.3917(3) to 11.2114(2) ?, respectively. The depth profile of the lattice parameters as a function of the incident angle was consistent with vertical variation in the composition of In or Ga with depth in the absorbing layer. The variation of the lattice parameters was due to the difference between the ionic radius of In and Ga co-occupying at the same crystallographic site. According to the results of the depth profile of the refined parameters using GIXRD data, the bandgap of the CIGS absorber layer was graded over a range of 1.222 to 1.532 eV. This approach nondestructively guess the bandgap depth profile through the refinement of the lattice parameters using GIXRD data on the assumption that the changes of the lattice parameters or unit-cell volume follow a good approximation to Vegard’s law.
关键词： Vegard’s law,Cu(In1-xGax)Se2 absorbing layer,Depth profile,Bandgap grading,Glancing incidence X-ray diffraction technique
更新于2025-09-23 15:21:01