continuously increase with light illumination while the shortcircuit current ( J SC ) experiences a quick increase and then a decrease upon light exposure. The C -V measurements fi nd that light soaking can decrease the charge accumulation at the electrode interfaces. Essentially, the light soaking-decreased charge accumulation at electrode interface can be attributed to following two possible processes. First, the photogenerated carriers can neutralize the interfacial defects at electrode interface upon light illumination. Second, the migration of ions can change the built-in electric fi eld and then affects the charge accumulation at electrode interfaces. In particular, these two processes can largely increase the V OC by increasing interfacial potential barrier at electrode interfaces during light illumination. The time-dependent PL and frequency-dependent capacitance ( Cf ) fi nd that the bulk defects within perovskite fi lm are mainly positively charged and can be neutralized by photogenerated electrons upon light illumination. In particular, our frequency-dependent capacitance provides the fi rst direct evidence that light soaking can decrease bulk-electrical polarization within organo-metal halide perovskites. Especially, decreasing the bulk-electrical polarization causes a decrease on J SC in light soaking. However, neutralizing the defects at electrode interfaces and bulk perovskite fi lm can enhance the transport of the dissociated charge carriers to respective electrodes, increasing the FF during light illumination. Clearly, our experimental studies provide an in-depth understanding on internal coupling between electrode and bulk parameters in light soaking and hysteresis phenomena in perovskite solar cells under deviceoperating condition. Figure 1 shows the light soaking effects on device performance for perovskite solar cells. On initial light exposure the device shows a lower photovoltaic performance with V OC = 0.51 V, J SC = 18.34 mA cm −2 , FF = 53.1%, and power conversion effi ciency (PCE) = 4.97%. With continuous light exposure, device performance is signifi cantly improved over time. After ≈20 min of light soaking, the enhanced V OC = 0.83 V, J SC = 18.18 mA cm −2 , FF = 69.5% are obtained, resulting in a PCE = 10.49%. As we know, a continuous light illumination can cause heating and charge trapping in the development of light soaking and hysteresis effects. Here, our studies indicate that the light soaking and hysteresis effects come from charge trapping rather than heating. Specifi cally, we observe that the surface temperature of device can be increased from 26 to 42 °C when the cells are continuously exposed to light illumination. However, the device performance only slightly decreases, according to the J -V characteristics (inset in Figure 2 ), when the temperature increased to 42 ºC equivalent to the temperature produced by continuous light illumination. After removing the heating and cooling the device to room temperature, we can see that the device performance is again signifi cantly

Although great attention has been paid to wearable electronic devices in recent years, flexible lightweight batteries or supercapacitors with high performance are still not readily available due to the limitations of the flexible electrode inventory. In this work, highly flexible, bendable and conductive rGO-PEDOT/PSS films were prepared using a simple bar-coating method. The assembled device using rGO-PEDOT/PSS electrode could be bent and rolled up without any decrease in electrochemical performance. A relatively high areal capacitance of 448 mF cm−2 was achieved at a scan rate of 10 mV s−1 using the composite electrode with a high mass loading (8.49 mg cm−2), indicating the potential to be used in practical applications. To demonstrate this applicability, a roll-up supercapacitor device was constructed, which illustrated the operation of a green LED light for 20 seconds when fully charged.

There has been an emerging interest in stretchable power sources compatible with flexible/wearable electronics. Such power sources must be able to withstand large mechanical strains and still maintain function. Here we report a highly stretchable H3PO4-poly(vinyl alcohol) (PVA) polymer electrolyte obtained by optimizing the polymer molecular weight and its weight ratio to H3PO4 in terms of conductivity and mechanical properties. The electrolyte demonstrates a high conductivity of 3.4 x 10-3 S cm-1, and a high fracture strain at 410% elongation. It is mechanically robust with a tensile strength of 2 MPa and a Young's modulus of 1 MPa, and displays a small plastic deformation (5%) after 1000 stretching cycles at 100% strain. A stretchable supercapacitor device has been developed based on buckled polypyrrole electrodes and the polymer electrolyte. The device shows only a small capacitance loss of 5.6% at 30% strain, and can retain 81% of the initial capacitance after 1000 cycles of such stretching. ABSTRACT: There has been an emerging interest in stretchable power sources compatible with flexible/wearable electronics. Such power sources must be able to withstand large mechanical strains and still maintain function. Here we report a highly stretchable H 3 PO 4 -poly(vinyl alcohol) (PVA) polymer electrolyte obtained by optimizing the polymer molecular weight and its weight ratio to H 3 PO 4 in terms of conductivity and mechanical properties. The electrolyte demonstrates a high conductivity of 3.4×10 -3 S cm -1 , and a high fracture strain at 410% elongation. It is mechanically robust with a tensile strength of 2 MPa and a Young's modulus of 1 MPa, and displays a small plastic deformation (5%) after 1000 stretching cycles at 100% strain. A stretchable supercapacitor device has been developed based on buckled polypyrrole electrodes and the polymer electrolyte. The device shows only a small capacitance loss of 5.6% at 30%strain, and can retain 81% of the initial capacitance after 1000 cycles of such stretching.2

Despite the rapid increase of efficiency, perovskite solar cells (PSCs) still face some challenges, one of which is the current-voltage hysteresis. Herein, it is reported that yttrium-doped tin dioxide (Y-SnO ) electron selective layer (ESL) synthesized by an in situ hydrothermal growth process at 95 °C can significantly reduce the hysteresis and improve the performance of PSCs. Comparison studies reveal two main effects of Y doping of SnO ESLs: (1) it promotes the formation of well-aligned and more homogeneous distribution of SnO nanosheet arrays (NSAs), which allows better perovskite infiltration, better contacts of perovskite with SnO nanosheets, and improves electron transfer from perovskite to ESL; (2) it enlarges the band gap and upshifts the band energy levels, resulting in better energy level alignment with perovskite and reduced charge recombination at NSA/perovskite interfaces. As a result, PSCs using Y-SnO NSA ESLs exhibit much less hysteresis and better performance compared with the cells using pristine SnO NSA ESLs. The champion cell using Y-SnO NSA ESL achieves a photovoltaic conversion efficiency of 17.29% (16.97%) when measured under reverse (forward) voltage scanning and a steady-state efficiency of 16.25%. The results suggest that low-temperature hydrothermal-synthesized Y-SnO NSA is a promising ESL for fabricating efficient and hysteresis-less PSC.

Common fabrication techniques typically require multiple and complex MEMS processing steps to create 3D electrode architectures. Here we report on the use of Additive Fabrication metal printing based on Selective Laser Melting (SLM) technology to produce 3D titanium interdigitated electrodes. This was used as a platform to deposit polypyrrole and the resultant structure was evaluated for use as a capacitive electrode. We also demonstrate a solid-state interdigitated supercapacitor using a poly(vinyl alcohol) (PVA)-H3PO4 polymer electrolyte.

With the surge of interest in miniaturized implanted medical devices (IMDs), implantable power sources with small dimensions and biocompatibility are in high demand. Implanted battery/supercapacitor devices are commonly packaged within a case that occupies a large volume, making miniaturization difficult. In this study, we demonstrate a polymer electrolyte-enabled biocompatible magnesium-air battery device with a total thickness of approximately 300 μm. It consists of a biocompatible polypyrrole-para(toluene sulfonic acid) cathode and a bioresorbable magnesium alloy anode. The biocompatible electrolyte used is made of choline nitrate (ionic liquid) embedded in a biopolymer, chitosan. This polymer electrolyte is mechanically robust and offers a high ionic conductivity of 8.9 x 10-3 S cm-1. The assembled battery delivers a maximum volumetric power density of 3.9 W L-1, which is sufficient to drive some types of IMDs, such as cardiac pacemakers or biomonitoring systems. This miniaturized, biocompatible magnesium-air battery may pave the way to a future generation of implantable power sources. Abstract:With the surge of interest in miniaturized implanted medical devices (IMDs), implantable power sources with small dimensions and biocompatibility are in high demand. Implanted battery/supercapacitor devices are commonly packaged within a case that occupies a large volume making miniaturization difficult. In this study, we demonstrate a polymer electrolyte enabled biocompatible magnesium-air battery device with a total thickness of approximately 300 µm. It consists of a biocompatible polypyrrole-para(toluene sulfonic acid) cathode and a bioresorbable magnesium alloy anode. The biocompatible electrolyte used is made of choline nitrate (ionic liquid) embedded in a biopolymer, chitosan. This polymer electrolyte is mechanically robust and offers a high ionic conductivity of 8.9×10 -3 S cm -1 . The assembled battery delivers a maximum volumetric power density of 3.9 W L -1 , which is sufficient to drive some types of IMDs such as cardiac pacemakers or bio-monitoring systems. This miniaturized, biocompatible magnesium-air battery may pave a way to the future generation of implantable power sources.

Biodegradable active implantable devices can be used to diagnose and/or treat disease and eventually disappear without surgical removal. If an "external" energy source is required for effective operation then a biocompatible and biodegradable battery would be ideal. In this study, a partially biodegradable Mg-air bioelectric battery (biobattery) is demonstrated using a silk fibroin-polypyrrole (SF-PPy) film cathode coupled with bioresorbable Mg alloy anode in phosphate buffered saline (PBS) electrolyte. PPy is chemically coated onto one side of the silk substrate. SF-PPy film shows a conductivity of ≈1.1 S cm−1 and a mild catalytic activity toward oxygen reduction. It degrades in a concentrated buffered protease XIV solution, with a weight loss of 82% after 15 d. The assembled Mg-air biobattery exhibits a discharge capacity up to 3.79 mA h cm−2 at a current of 10 μA cm−2 at room temperature, offering a specific energy density of ≈4.70 mW h cm−2. This novel partially biodegradable battery provides another step along the route to biodegradable batteries. Abstract:Biodegradable active implantable devices can be used to diagnose and/or treat disease and eventually disappear without surgical removal. If an "external" energy source is required for effective operation then a biocompatible and biodegradable battery would be ideal. In this study, a partially biodegradable Mg-air bioelectric battery (bio-battery) was demonstrated using a silk fibroin-polypyrrole (SF-PPy) film cathode coupled with bioresorbable Mg alloy anode in phosphate buffered saline (PBS) electrolyte. Polypyrrole (PPy) is chemically coated onto one side of the silk substrate. SF-PPy film shows a conductivity of ~1.1 S cm -1 and a mild catalytic activity towards oxygen reduction. It degrades in a concentrated buffered 2 protease XIV solution, with a weight loss of 82% after 15 days. The assembled Mg-air biobattery exhibit a discharge capacity up to 3.79 mA h cm -2 at a current of 10 µA cm -2 at room temperature, offering a specific energy density of ∼4.70 mW h cm -2 . This novel partially biodegradable battery provides another step along the route to biodegradable batteries.

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