In this work, high-performance four-terminal solution-processed tandem solar cells were fabricated by using dyesensitized solar cells (DSSCs) as top-cells and lead sulfide (PbS) colloidal quantum dot solar cells (CQDSCs) as bottom-cells. For dye-sensitized top-cells, three different dye combinations were used while the titanium dioxide (TiO 2 ) scattering layer was removed to maximize the transmission. For the PbS bottom-cells, quantum dots with different sizes were compared. Over 12% power conversion efficiency has been achieved by using the XL dye mixture and 890 nm PbS QDs, which shows a significant efficiency enhancement when compared to single DSSC or CQDSC subcells.

Indenofluorene‐extended tetrathiafulvalenes (IF‐TTFs) comprise a class of π‐conjugated sensitizers that exhibit strong absorptions in the visible region and two reversible one‐electron oxidations. Herein we present the synthesis and optical as well as redox properties of novel IF‐TTF donor‐acceptor scaffolds that were integrated in dye‐sensitized solar cells (DSCs) via anchoring of a carboxylic acid end‐group on the scaffolds to TiO2. Synthetically, the scaffolds were constructed by Sonogashira coupling reactions between an iodo‐functionalized IF‐TTF and an acceptor moeity containing a terminal alkyne. These very first IF‐TTF based candidates for DSCs exhibited high performances, in particular a dye incorporating a benzothiadiazole acceptor moiety, showing a conversion efficiency of 6.4 %. This result signals that IF‐TTF derivatives present a promising class of compounds for further structural modifications. Such modifications will benefit from the readiness of the iodo‐funcitonalized IF‐TTF building block to undergo Pd‐catalyzed coupling reactions.

No abstract

Over the past decade, perovskite solar cells have travelled an amazing way towards high efficiency. However, a major roadblock remaining is the operational stability, while achieving technological maturity and proving real-world stability is crucial to gain trust among investors. In that sense, it is of high interest to be able to predict the operational lifetime, which needs to be in the range of years or decades, within an experimentally reasonable timeframe. Yet, peculiarities of perovskite solar cells’ ageing behaviour lead to severe difficulties in translating the results of indoor tests to their outdoor counterpart. In particular, transient processes cause diverse results among different ageing tests.Here, for the first time, we show a complete set of constant illumination indoor testing, cycled illumination indoor testing and real-world outdoor testing on equal in-house devices. Exemplarily, we compare two different types of perovskite solar cells, in which only the hole-transport layer is varied. Despite this small change, the devices show distinctly different transient behaviour. In either case, the commonly used constant illumination experiments fail to predict the outdoor behaviour of the cell. Yet, we observe a good correlation between the cycled illumination test and the outdoor behaviour of one of the two solar cells, while this is not the case for the other system. This result highlights the urge for further research on how to perform meaningful accelerated indoor tests to predict the outdoor lifetime of perovskite solar cells.