Printable Zinc-Ion Hybrid Micro-Capacitors for Flexible Self-Powered Integrated Units

Highlights This work is a new guide for the design of on-chip energy integrated systems toward the goal of developing highly safe, economic, and long-life smart wearable electronics. The biomass kelp-carbon based on unique 3D micro-/nanostructure combined with multivalent ion storage contributes to high capacity of the Zn-ion hybrid capacitor. The flexible solar-charging self-powered system with printed Zn-ion hybrid micro-capacitor as energy storage module exhibits fast photoelectric conversion/storage rate, good mechanical robustness, and cyclic stability. Electronic supplementary material The online version of this article (10.1007/s40820-020-00546-7) contains supplementary material, which is available to authorized users.


S1.2 OSC fabrication
The structure of the flexible OSC is PET/ITO/ZnO/PBDB-T-2F:IT-4F/MoO3/Ag. Isopropanol and acetone were used to clean the substrates. The electron transport layer ZnO was spun on the ITO/PET at 3500 rpm for 60 s and annealed at 130 °C for 15 min. Then, the PBDB-T-2F:IT-4F films were prepared on the top of ZnO by spin coating from a chlorobenzene solution (containing 0.5 vol% of 1,8-diiodooctane) with PBDB-T-2F:IT-4F (10 mg/mL: 10 mg/mL) at 1500 rpm for 60 s, and then annealed at 100 °C for 10 min in a glove box filled with nitrogen. Finally, MoO3 (7 nm) and Ag (100 nm) were thermally evaporated on the active layer.

S1.3 Characterizations
SEM (Nova NanoSEM 450, FEI Corporation, Netherlands) equipped with EDS and TEM (Tecnai G2 F30, FEI Corporation, Netherlands) were used to observe the micro-morphologies of samples and analyze the element compositions. The microstructure of kelp-carbon was characterized by Raman spectroscopy using a LabRAM HR800 spectrometer (HORIBA Jobin Yv on Corporation, France) with a Nd:YAG laser at a wavelength of 532 nm. XRD (X'Pert PRO, PANalytical B.V., Netherlands) was used to analyze the crystal structure of materials and electrodes. The element composition of the kelp-carbon was identified by XPS collected on an AXIS Ultra DLD-600W spectrometer (Kratos Corporation, Japan) with a monochromatic Al Kɑ X-ray source. N2 adsorption/desorption measurements were carried out at 77 K using an ASAP 2020 surface area and porosity analyzer (Micromeritics Instrument Corporation, USA). Before testing, the samples were degassed at 350 °C overnight. CV tests were performed in the voltage range between 0.1 and 1.7 V at scan rates from 5 to 200 mV s -1 using a Gamry Interface 1000 electrochemical workstation. EIS measurements were executed in the frequency range from 10 -3 to 10 5 Hz at open circuit potential with an AC amplitude of 5 mV. GCD tests were carried out on Arbin BT 2000 Battery Testing System in the voltage window of 0.1 to 1.7 V at current densities from 0.1 to 10 A g -1 . The cycle stability tests were performed at 2 A g -1 .

S1.4 Calculations
The specific capacity (Cm, mAh g -1 ) for the ZHCs can be calculated from discharge curve by Eq. (S1): where I (mA), t (h) represent the current and time of discharge process, and m (g) stands for the mass of cathode material.
Energy density (E, Wh kg -1 ) and power density (P, W kg -1 ) for the ZHCs were calculated by Eqs. (S2) and (S3), respectively: where U (V) and t (h) stand for the discharge voltage after ohmic drop and discharge time.
The areal capacity (CA, mAh cm -2 ) of the micro-ZHCs can be calculated from GCD curves via Eq. (S4): where I (mA) and t (h) represent the current and time of discharge process, and A (cm 2 ) stand for the total area of cathode and anode.
The energy density EA (mWh cm -2 ) and power density PA (mW cm -2 ) were obtained from the Eqs. (S5) and (S6), respectively: where U (V) and t (h) stand for the discharge voltage after ohmic drop and discharge time.
The overall efficiency of energy conversion and storage (ηoverall) can be calculated according to Eq. (S7): where E, P, S, and t are the discharge energy after solar-charging (Wh), the light intensity (W m -2 ), the effective area of solar cell (m 2 ), and the duration of solar-charging (h), respectively. The conductivity of the hydrogel electrolyte was evaluated by the electrochemical impedance spectroscopy using a Gamry Interface 1000 electrochemical workstation in the frequency range of 10 -3 to 10 5 Hz at an AC amplitude of 5 mV. In the measurement, the hydrogel electrolyte was sandwiched between two stainless steel sheets, and the conductivity σ (mS cm -1 ) was calculated by Eq. (S8),

S2 Supplementary Figures and Tables
where L (cm) is the distance between the two stainless steel sheets, Rb (Ω) is the bulk resistance (intercept at Z´ axis), and S is the contact area (cm 2 ) between electrolyte and stainless steel sheets. The total conductivity (σ) of the hydrogel electrolyte is calculated to be 12.2 mS cm -1 . Electronic conductivity of the hydrogel electrolyte was determined by the direct current (DC) polarization method under an applied DC voltage of 10 mV, which is on the order of 10 -5 S cm -1 , thus the electronic conductivity can be ignored, and the ionic conductivity of the hydrogel electrolyte can be determined to be 12.2 mS cm -1 .  =21.2%

Fig. S16
Cycling stability of the integrated unit at a solar-charging intensity of 4.14 mW cm -2 and discharge current density of 2 mA cm -2 The areal performance of micro-ZHC is calculated based on the total area of the cathode and anode; the volumetric performance of micro-ZHC is calculated based on the total volume of the cathode and anode.