Validation of a fast, simple and open-source approach to analyse passing nanoliter droplets using Bonsai visual programming language, towards high-throughput droplet-based microfluidic experiments with automated droplet interrogation in real-time.

Microfluidic-based platforms have become a hallmark for chemical and biological assays, empowering micro- and nano-reaction vessels. The fusion of microfluidic technologies (digital microfluidics, continuous-flow microfluidics, and droplet microfluidics, just to name a few) presents great potential for overcoming the inherent limitations of each approach, while also elevating their respective strengths. This work exploits the combination of digital microfluidics (DMF) and droplet microfluidics (DrMF) on a single substrate, where DMF enables droplet mixing and further acts as a controlled liquid supplier for a high-throughput nano-liter droplet generator. Droplet generation is performed at a flow-focusing region, operating on dual pressure: negative pressure applied to the aqueous phase and positive pressure applied to the oil phase. We evaluate the droplets produced with our hybrid DMF–DrMF devices in terms of droplet volume, speed, and production frequency and further compare them with standalone DrMF devices. Both types of devices enable customizable droplet production (various volumes and circulation speeds), yet hybrid DMF–DrMF devices yield more controlled droplet production while achieving throughputs that are similar to standalone DrMF devices. These hybrid devices enable the production of up to four droplets per second, which reach a maximum circulation speed close to 1540 µm/s and volumes as low as 0.5 nL.

Cu2ZnSnS4 (CZTS) is a promising kesterite semiconductor for sustainable photovoltaic applications, offering advantages such as high optical absorption, bandgap tunability, and eco-friendly, earth-abundant elements. However, while solution-processed CZTS has shown potential, key gaps remain in understanding their optoelectronic properties, particularly how sulfur (S) and selenium (Se) influence phase segregation and bandgap grading. Furthermore, the wide-bandgap CZTS suffers from a significant open-circuit voltage (VOC) deficit, limiting its efficiency. In this study, we fabricated solution-processed wide-bandgap Ag0.1(Cu0.9)2 ZnSnS4 solar cells, achieving a remarkably high VOC of 770 mV [58.5% of (VOCSQ)]. We compared the pure-sulfide wide-bandgap films, which formed a single kesterite layer, with narrow-bandgap Ag0.1(Cu0.9)2ZnSn(S,Se)4 films, which exhibited a dual-layer structure. Advanced characterization techniques, including scanning electron microscopy and scanning transmission electron microscopy, revealed Zn-rich and Sn-rich phase segregation for narrow-bandgap films, while back-side Raman spectroscopy showed depth-dependent compositional gradients. The incorporation of Se in the narrow-bandgap films led to improved carrier dynamics, reduced defect density, and enhanced device performance, with a significant increase in efficiency compared to the wide-bandgap films. These findings emphasize how S and Se tuning can modulate phase behavior, enabling the design of CZTSSe materials with tailored bandgaps and optimized optoelectronic properties for high-efficiency, environmentally sustainable solar cells.

Rear interface passivation on submicrometer Cu(In,Ga)Se₂ (CIGS) solar cells through nanopatterned dielectric layers has enabled performance gains. The combined optimization of the rear contact interface and the absorber properties enables high-efficiency ultrathin CIGS solar cells. However, the absorber quality of a standard thin 2000 nm CIGS has not been suitably maintained in absorbers with thickness values around 500 nm. Establishing an optimized Na doping, absorber crystallinity, and bandgap profile on such submicrometer CIGS solar cells has been challenging. Moreover, the Na doping may also be influenced by the rear contact architectures implemented in passivated solar cells, e.g., affecting the diffusion of Na from the soda-lime glass. Nonetheless, a proper Na supply into CIGS is critical for an optimized absorber quality. Therefore, this study evaluates the impact of the amount of Na supply controlled through a NaF precursor layer on a rear passivated ultrathin CIGS solar cell. The NaF layer thickness leading to the best performance solar cells in this study, attributed to high absorber crystallinity and low ordered vacancy compound content, is lower than that used in standard thin 2000 nm cells. It suggests that the transition to ultrathin solar cells is not straightforward, and the cell architecture influences the conditions to reach the optimum absorber properties.