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In this manuscript, we give an overview of the main insights into our growth procedure for kesterite solar cells and show the possibilities that are provided by this approach. The importance of using Cu–Sn alloy instead of elemental Sn and Cu in the precursor is shown. We discuss how the alloy approach stabilises the composition and helps guide the process along a preferred reaction pathway. A summary of our previously reported findings in the context of our latest results on kesterite solar cells prepared from Cu–Sn alloyed precursors is drawn. The positive impact of an alloy precursor configuration on the formation pathway, process control, and process resilience is demonstrated. Furthermore, a new optimisation strategy for kesterite, based on the reported pathway, is discussed, including a smooth phase transition from Cu-rich to Cu-poor kesterite. Finally, we demonstrate results on buffer optimisation and the application of a promising hybrid buffer configuration of CdS/Zn(O,S), which can reduce the optical losses in the solar cell structure.

Sulfur/selenium grading is a widely used optimization strategy in kesterite thin-film solar cells to obtain a bandgap-graded absorber material and to optimize optical and electrical properties of the solar-cell device. In this work, we present a novel approach to introduce a [S]/([S] + [Se]) grading for Cu

The algebraic properties of the combination of probabilistic choice and nondeterministic choice have long been a research topic in program semantics. This paper explains a formalization in the Coq proof assistant of a monad equipped with both choices: the geometrically convex monad. This formalization has an immediate application: it provides a model for a monad that implements a non-trivial interface which allows for proofs by equational reasoning using probabilistic and nondeterministic effects. We explain the technical choices we made to go from the literature to a complete Coq formalization, from which we identify reusable theories about mathematical structures such as convex spaces and concrete categories, and that we integrate in a framework for monadic equational reasoning., 28 pages, submitted

This work reports a growth process for tuning the formation pathway and final composition of kesterite Cu2ZnSnSe4 (CZTSe) thin film absorbers. By adjusting the as-grown composition of the precursor, the kesterite formation can be started in a Cu-rich, stoichiometric, or Cu-poor environment. During the hightemperature stage of the annealing process, incorporation or loss of SnSe2–x vapor at the layer is used to achieve an in-process composition shift during further kesterite growth (e.g., Cu-rich to Cu-poor/Cu-poor toward Cu-rich). This approach partially decouples the composition of the as-grown precursor and the final absorber, which, thus, can be tuned independently. The film growth, specifically the composition shift during the process, is tracked by interruption experiments. The influence of the starting composition of the precursor and the resulting absorber composition on the optoelectronic properties and device performance of the final solar cells is discussed. The results show a refined composition region for reduced Urbach tailing and lower VOC deficit. The best solar cells show efficiencies > 11% and a VOC deficit < 320 mV (relative to the Shockley–Queisser limit).

International audience; One can perform equational reasoning about computational effects with a purely functional programming language thanks to monads. Even though equational reasoning for effectful programs is desirable, it is not yet mainstream. This is partly because it is difficult to maintain pencil-and-paper proofs of large examples. We propose a formalization of a hierarchy of effects using monads in the Coq proof assistant that makes equational reasoning practical. Our main idea is to formalize the hierarchy of effects and algebraic laws like it is done when formalizing hierarchy of traditional algebras. We can then take advantage of the sophisticated rewriting capabilities of Coq to achieve concise proofs of programs. We also show how to ensure the consistency of our hierarchy by providing rigorous models. We explain the various techniques we use to formalize a rich hierarchy of effects (with nondeterminism, state, probability, and more), to mechanize numerous examples from the literature, and we furthermore discuss extensions and new applications.

For the fabrication of a kesterite-type CZTSe absorber material, stacked elemental-alloy layers (SEAL) precursor consisting of Cu-Sn alloy and elemental Zn layers offer the possibility of enhanced process control due to their advantages such as improvement of material homogeneity and suppression of the commonly observed Sn loss. In this study, the impact of selenium amounts during the annealing of a SEAL-type precursor with the configuration of Zn/Cu-Sn/Zn was demonstrated. The obtained results demonstrate how the selenium amount can indirectly be used to influence the absorber composition in the described annealing process and its direct impact on the opto-electronic properties of solar cells. This occurs due to the placement of elemental Sn in the vicinity of the sample during annealing that acts as a further source of SnSe

Injury to the spinal cord often disrupts long-distance axon tracts that link the brain and spinal cord, causing permanent disability. Axon regeneration is then prevented by a combination of inhibitory signals that emerge at the injury site and by a low capacity for regeneration within injured neurons. The corticospinal tract (CST) is essential for fine motor control but has proven refractory to many attempted pro-regenerative treatments. Although strategies are emerging to create relay or detour circuits that re-route cortical motor commands through spared circuits, these have only partially met the challenge of restoring motor control. Here, using a murine model of spinal injury, we elevated the intrinsic regenerative ability of CST neurons by supplying a pro-regenerative transcription factor, KLF6, while simultaneously supplying injured CST axons with a growth-permissive graft of neural progenitor cells (NPCs) transplanted into a site of spinal injury. The combined treatment produced robust CST regeneration directly through the grafts and into distal spinal cord. Moreover, selective optogenetic stimulation of regenerated CST axons and single-unit electrophysiology revealed extensive synaptic integration by CST axons with spinal neurons beyond the injury site. Finally, when KLF6 was delivered to injured neurons with a highly effective retrograde vector, combined KLF6/NPC treatment yielded significant improvements in forelimb function. These findings highlight the utility of retrograde gene therapy as a strategy to treat CNS injury and establish conditions that restore functional CST communication across a site of spinal injury.Significance StatementDamage to the spinal cord results in incurable paralysis because axons that carry descending motor commands are unable to regenerate. Here we deployed a two-pronged strategy in a rodent model of spinal injury to promote regeneration by the corticospinal tract, a critical mediator of fine motor control. Delivering pro-regenerative KLF6 to injured neurons while simultaneously transplanting neural progenitor cells to injury sites resulted in robust regeneration directly through sites of spinal injury, accompanied by extensive synapse formation with spinal neurons. In addition, when KLF6 was delivered with improved retrograde gene therapy vectors, the combined treatment significantly improved forelimb function in injured animals. This work represents important progress toward restoring regeneration and motor function after spinal injury.