Abstract
Despite the efficiencies above 20% achieved with (Ag,Cu)(In,Ga)Se
2
(ACIGS) solar cells, further efficiency improvements are necessary. One possibility is the implementation of a ...postdeposition treatment (PDT) process. The aim of this study is therefore to investigate the effect of rubidium‐fluoride (RbF)‐PDT on the performance and physical properties of the ACIGS absorber. For this purpose, the RbF source temperature of the PDT process of ACIGS films with Ag/(Ag+Cu) (AAC) ratios of 5% from a multistage co‐evaporation inline process was systematically varied. It was shown that the efficiency of the devices is reduced by the PDT process, unlike observed for Cu(In,Ga)Se
2
(CIGS) absorber, and is strongly influenced by the amount of rubidium. The behavior can be attributed to a strong reduction of the doping, which results from a changed doping mechanism. Furthermore, evidence for the formation of an additional layer was found. In addition, deep level transient spectroscopy (DLTS) measurements were performed on the samples showing a strong signal at low temperatures. This minority trap signal is strongly influenced by the amount of Rb and shows a systematically changing energetic position towards the middle of the band gap and an increasing density. Based on pulse variation measurements, the associated defect could be identified as an extended defect, indicating a location of the defect at grain boundaries.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor ...is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI
PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI
as another composition, which shows higher efficiency of 23.5% compared to 20.9% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The thin‐film photovoltaic technology based on Cu(In,Ga)Se
2
(CIGS) has reached high conversion efficiencies exceeding 23%. The gallium gradient in the bulk and the amount of alkali metals in and ...between CIGS grains strongly affect the cell performance and therefore need to be accurately measured and quantified. ToF‐SIMS is well suited for this task, but the spatial resolution is strongly influenced by the measurement parameters, especially at the required micrometer and nanometer scales. Such highly resolved measurements on CIGS surfaces are challenging. For instance, small copper aggregations occur in SEM images recorded after a focused ion beam (FIB) cut and change the energy‐dispersive spectroscopy (EDS) results. SIMS systems that use an argon ion source generate Cu lamellas, which also influence the measurement. Both effects result from preferential sputtering. Cooling with liquid nitrogen can minimize this negative effect for both techniques. Recent developments in SIMS systems provide more options to avoid these effects. New sources, like the Bi liquid metal gun and cluster guns, are available. However, a systematic investigation on the effect of the ion sources on the sputter craters and the resulting measurement of CIGS absorber is necessary to choose an adequate setup. Thus, we performed a comparison of four different ion sources (argon ion gun, oxygen gun, cesium metal gun, and oxygen cluster gun) and measured CIGS depth profiles at three temperatures −120°C, −50°C, and room temperature (RT). We investigate the influence of these conditions not only on the resulting SIMS depth profile and quantification but also on the morphology of the sputter crater.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The thin‐film photovoltaic technology based on Cu(In,Ga)Se2 (CIGS) has reached high conversion efficiencies exceeding 23%. The gallium gradient in the bulk and the amount of alkali metals in and ...between CIGS grains strongly affect the cell performance and therefore need to be accurately measured and quantified. ToF‐SIMS is well suited for this task, but the spatial resolution is strongly influenced by the measurement parameters, especially at the required micrometer and nanometer scales. Such highly resolved measurements on CIGS surfaces are challenging. For instance, small copper aggregations occur in SEM images recorded after a focused ion beam (FIB) cut and change the energy‐dispersive spectroscopy (EDS) results. SIMS systems that use an argon ion source generate Cu lamellas, which also influence the measurement. Both effects result from preferential sputtering. Cooling with liquid nitrogen can minimize this negative effect for both techniques. Recent developments in SIMS systems provide more options to avoid these effects. New sources, like the Bi liquid metal gun and cluster guns, are available. However, a systematic investigation on the effect of the ion sources on the sputter craters and the resulting measurement of CIGS absorber is necessary to choose an adequate setup. Thus, we performed a comparison of four different ion sources (argon ion gun, oxygen gun, cesium metal gun, and oxygen cluster gun) and measured CIGS depth profiles at three temperatures −120°C, −50°C, and room temperature (RT). We investigate the influence of these conditions not only on the resulting SIMS depth profile and quantification but also on the morphology of the sputter crater.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•Solution deposition of Zn(O,S) buffer layers in presence of hydroxylamine and sodium persulfate.•Increase of Zn(O,S) growth rate and reduction of material consumption.•Application of Zn(O,S) as ...buffer layer on in-line deposited Cu(In,Ga)Se2.•Cell efficiencies close to 19% comparable to reference cells with CdS buffer.•Reaction kinetics more likely affected by N-hydroxyguanidine intermediates.
Cu(In,Ga)Se2-based solar cells achieve highest efficiencies up to 23.4% by using solution-grown Zn(O,S) as the buffer layer. State-of-the-art procedures for Zn(O,S) deposition based on the ammonia-thiourea approach are still characterized by a low growth rate and a high material consumption of reactants. One of the approaches to improve the Zn(O,S) deposition rate is the implementation of compounds leading to a much faster thiourea decomposition and thus to a higher availability of sulfide anions. In this work, we test the impact of oxidative and reductive additives, namely sodium peroxydisulfate Na2S2O8 and hydroxylamine NH2OH, respectively. The Zn(O,S) growth rate could be significantly increased and the consumption of reactants drastically reduced without compromising the performance of fabricated solar cell devices. The composition of the layers was quantified by time-of-flight secondary ion mass spectrometry measurements and the S/(S+O) molar ratio was found to vary between 0.65 and 0.85 depending on the thiourea and additive concentration. For cell preparation, in-line co-evaporated Cu(In,Ga)Se2 with RbF post-deposition treatment was used and conversion efficiencies up to 19%, comparable to reference cells with a CdS buffer, could be realized. We discuss the reaction mechanism and conclude for both additives that the resulting sulfide concentration increase evolves via formation of N-hydroxyguanidine intermediates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
All‐inorganic perovskites have emerged as promising photovoltaic materials due to their superior thermal stability compared to their heat‐sensitive hybrid organic–inorganic counterparts. In ...particular, CsPbI2Br shows the highest potential for developing thermally‐stable perovskite solar cells (PSCs) among all‐inorganic compositions. However, controlling the crystallinity and morphology of all‐inorganic compositions is a significant challenge. Here, a simple, thermal gradient‐ and antisolvent‐free method is reported to control the crystallization of CsPbI2Br films. Optical in situ characterization is used to investigate the dynamic film formation during spin‐coating and annealing to understand and optimize the evolving film properties. This leads to high‐quality perovskite films with micrometer‐scale grain sizes with a noteworthy performance of 17% (≈16% stabilized), fill factor (FF) of 80.5%, and open‐circuit voltage (VOC) of 1.27 V. Moreover, excellent phase and thermal stability are demonstrated even after extreme thermal stressing at 300 °C.
A spin‐forced (SF) method as a facile approach is proposed to control the crystallization kinetics of CsPbI2Br crystal growth, achieving a uniform, and high‐quality film. The perovskite film formation during spin‐coating and annealing is evaluated by optical in situ characterization. As a result, an efficiency of 17.0% with excellent thermal stability at 300 °C is achieved.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In order to improve the power conversion efficiency of thin-film solar cells, it is essential to identify and quantify their dominant loss mechanisms and, thus, guide experimental device ...optimization. We provide this functionality via loss analyses determined from computer-aided modeling and numerical device simulations. Since electrical and optical effects influence each other within solar cells, the consideration of an isolated parameter is often not sufficient for maximizing cell performance. Therefore, a holistic perspective, including both the effects, is developed. Its modeling is achieved by an interplay of an optical transfer-matrix method and a quasi-3-D electrical finite-element method. Optical refractive information and electrical resistivity data have been measured experimentally and put into the model in order to forecast device <inline-formula><tex-math notation="LaTeX">I\text{--}V</tex-math></inline-formula> curves. Finally, these <inline-formula><tex-math notation="LaTeX">I\text{--}V</tex-math></inline-formula> curves are used to assign and quantitatively calculate the loss mechanisms of grid shading, reflection, parasitic and incomplete absorption, local maximum power point mismatches, undergrid reverse currents, and ohmic losses. We verified our approach using thin-film CuIn<inline-formula><tex-math notation="LaTeX">_{1-x}</tex-math></inline-formula>Ga<inline-formula><tex-math notation="LaTeX">_{x}</tex-math></inline-formula>Se<inline-formula><tex-math notation="LaTeX">_{2}</tex-math></inline-formula> cells with a variable thick front contact made of aluminum-doped zinc oxide. This discussion guides laboratory work to the relevant loss mechanisms and enables to rapidly test new innovation ideas by means of numerical simulations.
One key aspect to further improve thin-film photovoltaic devices is the optimal sizing of the different layers, such as grids, transparent conducting oxides (TCOs), back contacts, and absorber ...materials, with respect to their mutual electrical influences. This article describes a novel quasi-3-D finite element method (FEM) tool on a digital twin, which is capable of simulating all electrical influences from a holistic perspective from semiconductor materials to device level. It yields a spatially resolved intradevice distribution of electrical potentials and currents, helping to understand the physical processes within solar cell devices. Experimentally inaccessible data, such as the breakdown of different loss mechanisms, can be provided. Moreover, the internal cell properties can be used for forecasting calculations of characteristic I-V curves. This process can also be reversed in a procedure called reverse engineering fitting. It allows to calculate backward from the external cell properties to the internal loss-exempt semiconductor material characteristics. Our approach is verified by semitransparent cells with a perovskite absorber, a silver rear metalization grid, and indium zinc oxide as a rear TCO. Our simulation predicts characteristic I-V curves with a coefficient of determination of well above 0.99 with respect to experimentally measured cells. The power conversion efficiency (PCE) can be forecast within a mean error of 0.18%<inline-formula><tex-math notation="LaTeX">_{\mathrm{abs}}</tex-math></inline-formula> at absolute PCEs around 13% for different TCO and grid thicknesses. The advantage of our FEM approach in contrast to a single-diode equivalent circuit model is demonstrated by considering I-V curve predictions for different cell sizes.
In this article, we discuss the leading thin-film photovoltaic (PV) technology based on the Cu(In,Ga)Se2 (CIGS) compound semiconductor. This contribution includes a general comparison with the ...conventional Si-wafer-based PV technology and discusses the basics of the CIGS technology as well as advances in world-record-level conversion efficiency, production, applications, stability, and future developments with respect to a flexible product. Once in large-scale mass production, the CIGS technology has the highest potential of all PV technologies for cost-efficient clean energy generation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
A holistic simulation of a photovoltaic system requires multiple physical levels - the optoelectronic behavior of the semiconductor devices, the conduction of the generated current, and the ...actual operating conditions, which rarely correspond to the standard testing conditions (STC) employed in product qualification. We present a holistic simulation approach for all thin-film photovoltaic module technologies that includes a transfer-matrix method, a drift-diffusion model to account for the p-n junction, and a quasi-three-dimensional finite-element Poisson solver to consider electrical transport. The evolved digital model enables bidirectional calculation from material parameters to non-STC energy yield and vice versa, as well as accurate predictions of module behavior, time-dependent top-down loss analyses and bottom-up sensitivity analyses. Simple input data like current-voltage curves and material parameters of semiconducting and transport layers enables fitting of otherwise less-defined values. The simulation is valuable for effective optimizations, but also for revealing values for difficult-to-measure parameters.
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