In this study, Deep Level Transient Spectroscopy (DLTS) measurements have been performed on Cu(In,Ga)Se2 (CIGS) solar cells from an inline co-evaporation system. The focus of this investigation is directed on the effect of rubidium-fluoride (RbF)-post-deposition treatment (PDT) on the defects in the CIGS absorber layer. Different traps can be identified and their properties are calculated. Herein, different methods of evaluations have been used to verify the results. Specifically, one minority trap around 400 meV was found to show a significant reduction of the trap density due to the alkali treatment. In contrast, a majority trap at approximately 600 meV is unaffected.

Topology optimization is typically used for suitable design suggestions for objectives like mean compliance, mean temperature, or model analysis. Some modern modeling technics in topology optimization require a nodal based material interpolation. Therefore this article is referred to a continuous material interpolation in topology optimization. To cover a smooth and differentiable density field, we address trigonometric shape functions which are infinitely differentiable. Furthermore, we extend a so-known global criteria method with a sharpening function based on binary cross-entropy, so that sharper solutions results. The proposed material interpolation is applied to different applications such as heat transfer, elasto static, and potential flow. Furthermore, these different objectives are together optimized using a multi-objective criterion.

Broadband microwave spectroscopy can probe material properties in wide spectral and temperature ranges. The quality of such measurements crucially depends on the calibration, which also removes from the obtained spectra signatures of standing waves. Here we consider cryogenic Corbino-type reflection measurements on superconductors close to the critical temperature. We show that the non-linear sample response, which relates to sample heating, can lead to strong signatures of standing waves even in a well-calibrated Corbino spectrometer. We demonstrate our findings with microwave measurements as a function of frequency, power, and temperature and for different length of the microwave transmission line. Finally we note such non-linear effects beyond the case of superconductors by probing a VO 2 thin film at the insulator-metal transition. arXiv:1810.07784v3 [cond-mat.supr-con]

Despite the efficiencies above 20% achieved with (Ag,Cu)(In,Ga)Se2 (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)Se2 (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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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.

We show that the concept of topology optimization for metallization grid patterns of thin-film solar devices can be applied to monolithically integrated solar cells. Different irradiation intensities favor different topological grid designs as well as a different thickness of the transparent conductive oxide (TCO) layer. For standard laboratory efficiency determination, an irradiation power of $$1000\,\mathrm {W/m}^2$$ 1000 W / m 2 is generally applied. However, this power rarely occurs for real-world solar modules operating at mid-latitude locations. Therefore, contact layer thicknesses and also lateral grid patterns should be optimized for lower irradiation intensities. This results in material production savings for the grid and TCO layer of up to 50 % and simultaneously a significant gain in yield of over $$1\,\%$$ 1 % for regions with a low annual mean irradiation. Graphical Abstract