A multi-method approach was used for the investigation and comparison of alkali-activated slag binders (AAS), pure slag and ordinary Portland cement (OPC). X-ray fluorescence, X-ray powder diffraction, granulometry, calorimetry, thermo-gravimetric analysis and environmental scanning electron microscope investigations of the microstructure with energy dispersive X-ray analyses were used to characterise the cements and their hydrate phases. In addition, the chemical composition of the pore solution, including the different sulphur-containing ions, was analysed. The precipitation mechanisms during binder hydration in the AAS and OPC systems exhibit significant differences: in AAS the formation of the ‘outer product’ C-S-H is much faster than in OPC. The high Si concentrations in the pore solution during the early hydration of AAS are related to the fast dissolution of Na-metasilicate. The fast reaction of Na is an important factor for the voluminous precipitation of C-S-H within the interstitial space already during the first 24 h. In addition to the Na-metasilicate component, the high fineness of the slag represents a further important factor for the fast hydration of AAS. The small slag particles (< 2 μm) are completely dissolved or hydrated within the first 24 h, whereas hydration of the larger particles is much slower. The fast formation of a gel-like matrix in AAS is the product of a fast ‘through solution’ precipitation, which contrasts with the slower dissolution-precipitation mechanism of a ‘topotactic’ growth of C-S-H in OPC. The chemical and mineralogical characterisation of solid and liquid phases and their changes with time are the basis for thermodynamic modelling of the corresponding hydration process, which is presented in a second paper.

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Postdeposition treatments (PDTs) with sodium fluoride (NaF) and potassium fluoride (KF) were introduced as a way to improve the efficiency of Cu­(In,Ga)­Se2 (CIGS) based solar cells. Here, we apply postdeposition treatments with rubidium fluoride (RbF) to low-temperature coevaporated CIGS absorbers after a first PDT with NaF and compare the effects of the addition of Rb and K on the solar cell performance and material properties of the CIGS films. KF and RbF PDTs lead to similar improvements in the open-circuit voltage (V oc) and fill factor (FF), while allowing a reduction of the thickness of the cadmium sulfide (CdS) buffer layer without loss in electronic performance. KF and RbF PDTs lead to comparable modifications of the morphology and composition of the CIGS films. After the PDT, K and Rb accumulate in a nanopatterned copper-poor secondary phase at the CIGS surface, while also diffusing within the CIGS layer and strongly reducing the concentration of lighter alkali element sodium. These findings corroborate theoretical calculations published by another group, which predicted the segregation of potassium indium selenide (KInSe2) and rubidium indium selenide (RbInSe2) at CIGS surfaces under the used PDT conditions.

kesterite material with its optimal bandgap and absorption coefficient. [2] Alkali treatment of kesterite solar cells is one of the measures to reduce the high V OC -deficit and most of today's >10% efficiency kesterite devices utilize the beneficial effects of alkali elements on absorber layer morphology and optoelectronic properties. So far the most research attention has been paid to sodium, resulting in many thorough investigations which revealed grain size enhancement, passivation of grain boundaries, and an increase in net hole concentration as the major beneficial effects of sodium treatments. [3][4][5][6] Also lithium addition has shown to improve device performance by boosting the electronic quality of the CZTSSe absorber material and grain boundaries. [7] First studies on the effect of potassium addition confirmed advantageous effects on kesterite absorber growth and optoelectronic properties similar to Na. [8,9] Several studies comparing different alkali elements and their effect on solar cell properties and device performance have recently been published. [10][11][12][13] Table 1 compares the effects on device performance by extracting a ranking of the various alkali elements in each publication in the order of their capability to improve device performance. It is apparent from these rankings that no consistent experimental results have been obtained, which triggers two questions: (i) Why do the published results differ so much? (ii) Which alkali element possesses the highest potential for efficiency improvements?This paper aims to unveil the discrepancy between the recently published results comparing the effects of alkali treatments on device performance. Our hypothesis is that each alkali element requires a different absorber composition to achieve the highest PV performance and we therefore prepared a comprehensive set of samples with different alkali elements and alkali concentrations as well as various metal ratios. All samples were thoroughly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma-mass spectrometry (ICP-MS), as well as current-voltage (J-V), capacitance-voltage (C-V), time-resolved photoluminescence (TRPL), and external quantum efficiency (EQE) measurements.The methodology used for absorber synthesis is based on the solution process described elsewhere, [14] allowing for accurate alkali incorporation by simply adding alkali chlorides to the solution. [15] Figure 1a illustrates the matrix of sample compositions prepared with five different alkali elements: lithium (Li), Sodium treatment of kesterite layers is a widely used and efficient method to boost solar cell efficiency. However, first experiments employing other alkali elements cause confusion as reported results contradict each other. In this comprehensive investigation, the effects of absorber composition, alkali element, and concentration on optoelectronic properties and device performance are investigated. Experimental results show that in the r...

Super sulphated cements (SSC) are based on industrial by-products of the steel manufacture and save natural raw materials, thus decreasing the overall energy required to produce a cementitious material as well as carbon dioxide emissions. Compared to ordinary portland cement (OPC), SSC has an increased resistance to sulphate attack and a low heat of hydration. SSC is obtained from granulated blast furnace slag and activated by the addition of anhydrite and small amounts of an alkaline activator. Slags with a high amount of Ah0 3 and CaO react faster and give higher compressive strength. The target of this study was to increase the early compressive strength of a low reactive slag (LR-SSC) in order to get a comparable value as for a high reactive slag (HR-SSC).