Effects of Flexible Conjugation-Break Spacers of Non-Conjugated Polymer Acceptors on Photovoltaic and Mechanical Properties of All-Polymer Solar Cells

All-polymer solar cells(all-PSCs)possess attractive merits including superior thermal stability and mechanical flexibility for large-area roll-to-roll processing.Introducing flexible conjugation-break spacers(FCBSs)into backbones of polymer donor(P_(D))or polymer acceptor(P_(A))has been demonstrated as an efficient approach to enhance both the photovoltaic(PV)and mechanical properties of the all-PSCs.However,length dependency of FCBS on certain all-PSC related properties has not been systematically explored.In this regard,we report a series of new non-conjugated P_(A)s by incorporating FCBS with various lengths(2,4,and 8 carbon atoms in thioalkyl segments).Unlike com-mon studies on so-called side-chain engineering,where longer side chains would lead to better solubility of those resulting polymers,in this work,we observe that the solubilities and the resulting photovoltaic/mechanical properties are optimized by a proper FCBS length(i.e.,C2)in P_(A) named PYTS-C2.Its all-PSC achieves a high efficiency of 11.37%,and excellent mechanical robustness with a crack onset strain of 12.39%,significantly superior to those of the other P_(A)s.These results firstly demonstrate the effects of FCBS lengths on the PV performance and mechanical properties of the all-PSCs,providing an effective strategy to fine-tune the structures of P_(A)s for highly efficient and mechanically robust PSCs.

Detection of Graphene Cracks By Electromagnetic Induction,Insensitive to Doping Level

Detection of cracks is a great concern in production and operation processes of graphene based devices to ensure uniform quality.Here,we show a detection method for graphene cracks by electromagnetic induction.The time varying magnetic field leads to induced voltage signals on graphene,and the signals are detected by a voltmeter.The measured level of induced voltage is correlated with the number of cracks in graphene positively.The correlation is attributed to the increasing inductive characteristic of defective graphene,and it is verified by electromagnetic simulation and radio frequency analysis.Furthermore,we demonstrate that the induced voltage signal is insensitive to the doping level of graphene.Our work can potentially lead to the development of a high-throughput and reliable crack inspection technique for mass production of graphene applications.

Preface: Nano/Micro Structures in Application of Computational Mechanics

Many important issues of structures,such as lattice mismatch,compatibility,orientation,evolution,phase transition,surfaces,interfaces,defects,and domain engineering,have attracted considerable interest.The corresponding mechanisms of these issues have not been fully elucidated.Computational mechanics has been widely used to investigate such complexities in nano/microstructures in recent decades.In this special issue,leading experts in their respective fields are invited to present their new insight into the theoretical calculation and modeling of nano/microstructures.Nine articles are collected.A brief introduction on each article is provided below.

Multi-directionally wrinkle-able textile OLEDs for clothing-type displays

A clothing-type wearable display can be utilized in fashion,bio-healthcare,and safety industries as well as smart textiles for the internet of things(IoTs)and wearable devices.In response to this trend,we demonstrate a textile display that can endure the active movements of a human body.It can be applied to any kind of textile,and is durable against conditions such as rain,sweat,and washing.As a key technology for realizing the multi-directional wrinkle-able textile display,we fabricated a stress-lowering textile platform with an ultrathin planarization layer replicated from the flat surface of glass.An elastomeric strain buffer for reducing mechanical stress is also inserted into the textile platform.Here,organic light-emitting diodes(OLEDs)with red,green and blue color,thin film transistors(TFTs)fabricated at a low temperature below 150℃,and a washable encapsulation layer blocking both gas and liquid were demonstrated on the textile platform.

On-skin and tele-haptic application of mechanically decoupled taxel array on dynamically moving and soft surfaces

To accurately probe the tactile information on soft skin,it is critical for the pressure sensing array to be free of noise and inter-taxel crosstalk,irrespective of the measurement condition.However,on dynamically moving and soft surfaces,which are common conditions for on-skin and robotic applications,obtaining precise measurement without compromising the sensing performance is a significant challenge due to mechanical coupling between the sensors and with the moving surface.In this work,multi-level architectural design of micro-pyramids and trapezoid-shaped mechanical barrier array was implemented to enable accurate spatiotemporal tactile sensing on soft surfaces under dynamic deformations.Trade-off relationship between limit of detection and bending insensitivity was discovered,which was overcome by employing micropores in barrier structures.Finally,in-situ pressure mapping on dynamically moving soft surfaces without signal distortion is demonstrated while human skin and/or soft robots are performing complicated tasks such as reading Braille and handling the artificial organs.