The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g. via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g. printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world.

Great advancements in the photovoltaic performance of polymer solar cells (PSCs) have been achieved through the synergistic effect of aromatic and heteroaromatic units incorporated into the backbone of a conjugated polymer. However, efficient donor polymers with electron-deficient nitrogen heterocycles (N-heterocycles) for PSCs have been relatively less explored in terms of number and diversity relative to thienoacene counterparts. In this report, we investigated, for the first time, pyrazine as an acceptor core for designing wide-bandgap (WBG) polymer donors poly-{2-(5-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b′]dithiophen-2-yl)-4-decylthiophen-2-yl)-5-(4-decyl-5-methylthiophen-2-yl)pyrazine} (P1) and poly-{2-(5-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b′]dithiophen-2-yl)-4-(2-ethylhexyl)thiophen-2-yl)-5-(4-(2-ethylhexyl)-5-methylthiophen-2-yl)pyrazine} (P2) having different alkyl side chains for use in non-fullerene (NF) PSCs. These polymers demonstrated deep frontier energy levels and wide bandgaps (∼2.05 eV) because of the electron-withdrawing ability of the nitrogen atoms in their pyrazine core. Additionally, they also demonstrated stronger aggregation and enhanced coplanarity because of the noncovalent interaction between the nitrogen atom of the pyrazine and adjacent thiophene units. The optimized PSCs obtained by blending P1 and P2 with an NF acceptor, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC) exhibited impressive efficiencies of 7.6 and 8.1%, respectively. The observed variation in the performance was studied by various characterization methods. The superior photovoltaic performance of the P2 : ITIC blend originated from its distinctly optimized polymer design via regulation of its alkyl side chains, which led to downshifted frontier energy levels, a face-on orientation, and an optimum morphology compared with those of the P1 : ITIC blend. Our findings advance the understanding of the influence of incorporated pyrazine on the optoelectronic properties of polymer donors, and this structure–relationship study provides valuable insights for designing highly efficient copolymers with N-heterocycles.

Research studies based on flexible organic electronic devices regarding the relationship between carrier transport and molecular stacking are actively reported. For enhancing carrier transport and mechanical strength, new types of anthracene derivatives (ANT), exhibiting parallel dominant molecular stacking characteristics, are designed and synthesized. They show parallel dominant molecular stacking properties inducing excellent carrier transport through hybridization with perpendicular materials. They are introduced as electron transport layers (ETLs) for organic solar cells (OSCs), organic light emitting diodes (OLEDs), and organic nano-generators (ONGs). Hybrid ETLs show excellent carrier transport characteristics, exhibiting minimized energy loss and suppressed carrier recombination resulting from relative resonance through partial polarization of ANT. Consequently, the power conversion efficiency (PCE) of the fabricated OSCs based on fullerene and non-fullerene systems reaches 9.6% and 11.4%, and the luminescence of OLEDs reaches up to 17 057 cd m⁻². In addition, flexible OSCs, OLEDs, and ONGs show improved output performance and mechanical strength due to excellent carrier transport. Especially, in flexible ONGs, high carrier transport can be helpful for enhancing output voltage by energy level shifting.