The combination of responsive microgels and Lab-on-Fiber devices represents a valuable technological tool for developing advanced optrodes, especially useful for biomedical applications. Recently, we have reported on a fabrication method, based on the dip coating technique, for creating a microgels monolayer in a controlled fashion onto the fiber tip. In the wake of these results, with a view towards industrial applications, here we carefully analyze, by means of both morphological and optical characterizations, the effect of each fabrication step (fiber dipping, rinsing, and drying) on the microgels film properties. Interestingly, we demonstrate that it is possible to significantly reduce the duration (from 960 min to 31 min) and the complexity of the fabrication procedure, without compromising the quality of the microgels film at all. Repeatability studies are carried out to confirm the validity of the optimized deposition procedure. Moreover, the new procedure is successfully applied to different kinds of substrates (patterned gold and bare optical fiber glass), demonstrating the generality of our findings. Overall, the results presented in this work offer the possibility to improve of a factor ~30 the fabrication throughput of microgels-assisted optical fiber probes, thus enabling their possible exploitation in industrial applications.

Integrating multi-responsive polymers such as microgels onto optical fiber tips, in a controlled fashion, enables unprecedented functionalities to Lab-on-fiber optrodes. The creation of a uniform microgel monolayer with a specific coverage factor is crucial for enhancing the probes responsivity to a pre-defined target parameter. Here we report a reliable fabrication strategy, based on the dip coating technique, for the controlled realization of microgel monolayer onto unconventional substrates, such as the optical fiber tip. The latter was previously covered by a plasmonic nanostructure to make it sensitive to superficial environment changes. Microgels have been prepared using specific Poly(N-isopropylacrylamide)-based monomers that enable bulky size changes in response to both temperature and pH variations. The formation of the microgel monolayer is efficiently controlled through the selection of suitable operating pH, temperature and concentration of particle dispersions used during the dipping procedure. The effect of each parameter has been evaluated, and the validity of our procedure is confirmed by means of both morphological and optical characterizations. We demonstrate that when the coverage factor exceeds 90%, the probe responsivity to microgels swelling/collapsing is significantly improved. Our study opens new paradigms for the development of engineered microgels assisted Lab-on-Fiber probes for biochemical applications.

Substoichiometric molybdenum oxide (MoO_x) has good potential as a hole-collecting layer in solar cells. In this paper, we report on the application of ultrathin evaporated MoO_x as a hole collector at the back side of two distinct photovoltaic technologies: polymeric and silicon heterojunction (SHJ). In the case of polymer solar cells, we test MoO_x as a hole transport layer in devices with inverted architecture. The higher transparency of the MoO_x film, compared to the commonly used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), allows an enhanced back reflected light into the photoactive layer, thus boosting the photogeneration, as found from the illuminated J-V and external quantum efficiency (EQE) curves. The higher fill factor (FF) of the MoO_x-based device also suggests an improved charge collection efficiency compared to the cells with PEDOT:PSS. As for SHJ solar cells, we show that MoO_x offers the means for dopant-free hole collection with both p-type and n-type Si wafers. In the present comparison over planar test structures with Ag back reflecting electrodes, we observe an efficiency gain of approximately 1% absolute against a baseline with a conventional p-type amorphous silicon hole collector. The gain is linked to the increased V_OC, which is likely due to the reduced recombination at the Si wafer.

Perovskite/silicon tandem solar cells have strong potential for high efficiency and low cost photovoltaics. In monolithic (two-terminal) configurations, one key element is the interconnection region of the two subcells, which should be designed for optimal light management and prevention of parasitic p/n junctions. We investigated monolithic perovskite/silicon-heterojunction (SHJ) tandem solar cells with a p/n nanocrystalline silicon/silicon-oxide recombination junction for improved infrared light management. This design can additionally provide for resilience to shunts and simplified cell processing. We probed modified SHJ solar cells, made from double-side polished n-type Si wafers, which included the proposed front-side p/n tunnel junction with the p-type film simultaneously functioning as selective charge transport layer for the SHJ bottom cell, trying different thicknesses for the n-type layer. Full tandem devices were then tested, by applying a planar n-i-p mixed-cation mixed-halide perovskite top cell, fabricated via low temperature solution methods to be compatible with the processed Si wafer. We demonstrate the feasibility of this tandem cell configuration over a 1 cm² area with negligible J-V hysteresis and a V_OC ~1.8 V, matching the sum of the V_OC-s contributed by the two components.

This work investigates the effect of interface traps on the impedance spectra of dopant-free silicon solar cells. The studied device consists of a crystalline silicon absorber with an a-Si:H/MoOx/ITO stack as the front passivating hole-collecting contact and an a-Si:H/LiF/Al stack as the rear passivating electron-collecting contact. Experimental measurements, including illuminated current–voltage (I–V) characteristics and impedance spectroscopy, were performed on the fabricated devices and after a soft annealing treatment. The annealed cells exhibit an increased open-circuit voltage and a larger Nyquist plot radius. To interpret these results, a numerical model was developed in a TCAD environment. Simulations reveal that traps located at the p/i interface (MoOx/i-a-Si:H) significantly affect the impedance spectra, with higher trap concentrations leading to smaller Nyquist plot circumferences. The numerical impedance curves were aligned to the experimental data, enabling extraction of the interfacial traps concentration. The results highlight the sensitivity of impedance spectroscopy to interfacial quality and confirm that the performance improvement after soft annealing is primarily due to reduced defect density at the MoOx/i-a-Si:H interface.

This work investigates the effect of interface traps on the impedance spectra of dopant-free silicon solar cells. The studied device consists of a crystalline silicon absorber with an a-Si:H/MoOx/ITO stack as the front passivating hole-collecting contact and an a-Si:H/LiF/Al stack as the rear passivating electron-collecting contact. Experimental measurements, including illuminated current–voltage (I–V) characteristics and impedance spectroscopy, were performed on the as fabricated devices and after a soft annealing treatment. The annealed cells exhibit an increased open-circuit voltage and a larger Nyquist plot radius. To interpret these results, a numerical model was developed in a TCAD environment. Simulations reveal that traps located at the p/i interface (MoOx/i-a-Si:H) significantly affect the impedance spectra, with higher trap concentrations leading to smaller Nyquist plot circumferences. The numerical impedance curves were aligned to the experimental data, enabling extraction of the interfacial traps concentration. The results highlight the sensitivity of impedance spectroscopy to interfacial quality and confirm that the performance improvement after soft annealing is primarily due to reduced defect density at the MoOx/i-a-Si:H interface.