Jeffrey M. Mativetsky

To reduce the harm of electronic waste, there is impetus to expand the use of biodegradable substrates, biocompatible materials, and battery-free devices. In this study, a piezoelectric paper composite is produced by integrating polyvinylidene fluoride-trifluoroethylene [P-(VDF-TrFE)] with the conducting polymer poly-(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) and wood fiber paper. It is shown that the combined effect of PEDOT:PSS and paper leads to an enhanced out-of-plane piezoelectric coefficient in P-(VDF-TrFE), without the need for electric poling. The enhanced piezoelectric performance arises from a synergistic templating effect of PEDOT:PSS and paper that induces a sharp increase in the population of edge-on β phase P-(VDF-TrFE) crystallites. The templating effect relies on supramolecular interactions between PSS and paper that lead to PEDOT enrichment and a linear PEDOT conformation at the interface with P-(VDF-TrFE). Computational modeling reveals that linear PEDOT promotes β phase PVDF growth over the α phase due to a greater availability of hydrogen bonds. The synergistic templating of P-(VDF-TrFE) on PEDOT:PSS-coated paper opens avenues for tuning the properties of piezoelectric paper.

Mask-integrated respiratory sensors are promising for noninvasive monitoring of respiratory health outside of clinical settings, for example, to support at-home patient monitoring and telemedicine. Studies have shown the feasibility of attaching flexible and off-the-shelf sensors to face masks; however, the potential benefits of incorporating sensor materials directly onto the breathable microfibrous mesh of face masks have hardly been explored. In this work, we integrate respiratory sensors on flat polyethylene terephthalate substrates and microfibrous polypropylene face masks using an ionic liquid gel (ILG) to detect changes in local humidity during breathing. Under a DC voltage, the ILG sensors exhibit a superlinear dependence of current on humidity, resulting in enhanced sensitivity at the high humidity levels found in exhaled breath. By varying the composition of the ILG, we find an inverse relationship between the sensing signal strength and sensing kinetics, offering insights into the sensing mechanisms. Freestanding ILG films are found to be resilient under mechanical strain with humidity sensing still possible at 120% strain. Devices that are scalably integrated onto face masks produce sensors that are four times less sensitive to extreme bending at an angle of 150°. Preliminary artificial intelligence (AI) analysis of breathing patterns identifies coughs that are interspersed with regular breathing with 91% accuracy, showing the potential of AI-supported wearable masks for autonomous symptom tracking.

The nanoscale interpenetrating electron donor–acceptor network in organic bulk heterojunction (BHJ) solar cells results in efficient charge photogeneration but creates complex 3D pathways for charge transport. At present, little is known about the extent to which out‐of‐plane charge flow relies on lateral electrical connectivity. In this work, a procedure, based on conductive atomic force microscopy, is introduced to quantify lateral current spreading during out‐of‐plane charge transport. Using the developed approach, the dependence of lateral spreading on BHJ phase separation, composition, and molecule type (small molecule vs polymer) is studied. In the small‐molecule BHJ, 7,7′‐(4,4‐bis(2‐ethylhexyl)‐4H‐silolo[3,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(6‐fluoro‐4‐(5′‐hexyl‐[2,2′‐bithiophen]‐5‐yl)benzo[c]‐[1,2,5]thiadiazole):(6,6)‐Phenyl‐C₇₁‐butyric acid methyl ester (p‐DTS(FBTTh₂)₂:PC₇₁BM), an increase is observed in lateral hole current spreading as the population of donor crystallites, bearing an edge‐on molecular orientation, is increased. When integrated into BHJs, the polymer donor poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) leads to greater lateral hole current spreading and more spatially uniform charge transport than the small‐molecule donor, owing to in‐plane charge transport along the polymer backbone. Through the newly introduced electrical characterization scheme, these experiments bring to light the role of lateral electrical connectivity in assisting charge navigation across BHJs.

This study reveals that a mixture of face-on and edge-on molecular orientations can be favorable for out-of-plane charge transport in solution processed bulk heterojunction organic solar cell active layers.

Although hybrid organic–inorganic halide perovskite solar cells have achieved extraordinary improvements over the past few years, questions remain about the role of grain boundaries. This article reports on the nanoscale point‐by‐point current–voltage mapping of photovoltaic characteristics in inverted methylammonium lead triiodide perovskite solar cells. These measurements reveal an increased open‐circuit voltage and shunt resistance, along with a suppressed short‐circuit photocurrent at grain boundaries and nearby regions. Support from nanoscale ionic strain and surface potential mapping suggests that local ion accumulation and downward band bending can facilitate charge separation, but hinder charge collection at grain boundaries.

Combined light and voltage stimulus triggers localized cation migration, nonlinear lattice deformation, and nanoscale structural rearrangement in perovskite films providing insight into perovskite optoelectronic device instability.