Three-Dimensional, Chemically Bonded Polypyrrole/Bacterial Cellulose/Graphene Composites for High-Performance Supercapacitors

Flexible energy storage systems have recently attracted great interest for portable electronic devices. The functionalization of graphene provides vast platform in tailoring its nanostructure and properties for energy storage via facile processing. Here, we first demonstrate the development of chemically bonded graphene oxide and bacterial cellulose hybrid composite coated with polypyrrole for robust and high-efficiency supercapacitor electrodes. The as-prepared composites exhibited a highest electrical conductivity (1320 S m^–1) and the largest volumetric capacitance (278 F cm^–3) ever shown by carbon-based electrodes, along with 95.2% retention of 556 F g^–1 gravimetric capacitance over 5000 recycling tests in asymmetric supercapacitors. Impressively, the hybrid electrode contributed a 492 F g^–1 gravimetric capacitance and 93.5% retention over 2000 recycling in symmetric supercapacitors. The nanostructure and composition of the composites were found to play a crucial role for the performance of these three-dimensional, chemically bonded hybrid composite electrodes

Improved Efficiency of Bulk Heterojunction Polymer Solar Cells by Doping Low-Bandgap Small Molecules

We present performance improved ternary bulk heterojunction polymer solar cells by doping a small molecule, 2,4-bis­[4-(<i>N,N</i>-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIB-SQ), into the common binary blend of poly­(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM). The optimized power conversion efficiency (PCE) of P3HT:PC₇₁BM-based cells was improved from 3.05% to 3.72% by doping 1.2 wt % DIB-SQ as the second electron donor, which corresponds to ∼22% PCE enhancement. The main contributions of doping DIB-SQ material on the improved performance of PSCs can be summarized as (i) harvesting more photons in the low-energy range, (ii) increased exciton dissociation, energy transfer, and charge carrier transport in the ternary blend films. The energy transfer process from P3HT to DIB-SQ is demonstrated by time-resolved transient photoluminescence spectra through monitoring the lifetime of 700 nm emission from neat P3HT, DIB-SQ and blended P3HT:DIB-SQ solutions. The lifetime of 700 nm emission is increased from 0.9 ns for neat P3HT solution, to 4.9 ns for neat DIB-SQ solution, to 6.2 ns for P3HT:DIB-SQ blend solution

Comprehensive Study on Ultra-Wide Band Gap La₂O₃/ε-Ga₂O₃ p–n Heterojunction Self-Powered Deep-UV Photodiodes for Flame Sensing

Solar-blind UV photodetectors have outstanding reliability and sensitivity in flame detection without interference from other signals and response quickly. Herein, we fabricated a solar-blind UV photodetector based on a La2O3/ε-Ga2O3 p–n heterojunction with a typical type-II band alignment. Benefiting from the photovoltaic effect formed by the space charge region across the junction interface, the photodetector exhibited a self-powered photocurrent of 1.4 nA at zero bias. Besides, this photodetector demonstrated excellent photo-to-dark current ratio of 2.68 × 104 under 254 nm UV light illumination and at a bias of 5 V, and a high specific detectivity of 2.31 × 1011 Jones and large responsivity of 1.67 mA/W were achieved. Importantly, the La2O3/ε-Ga2O3 heterojunction photodetector can rapidly respond to flames in milliseconds without any applied biases. Based on the performances described above, this novel La2O3/ε-Ga2O3 heterojunction is expected to be a candidate for future energy-efficient fire detection

Simultaneous Improvement in Short Circuit Current, Open Circuit Voltage, and Fill Factor of Polymer Solar Cells through Ternary Strategy

We present a smart strategy to simultaneously increase the short circuit current (<i>J</i>_sc), the open circuit voltage (<i>V</i>_oc), and the fill factor (FF) of polymer solar cells (PSCs). A two-dimensional conjugated small molecule photovoltaic material (SMPV1), as the second electron donor, was doped into the blend system of poly­(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl (PC₇₁BM) to form ternary PSCs. The ternary PSCs with 5 wt % SMPV1 doping ratio in donors achieve 4.06% champion power conversion efficiency (PCE), corresponding to about 21.2% enhancement compared with the 3.35% PCE of P3HT:PC₇₁BM-based PSCs. The underlying mechanism on performance improvement of ternary PSCs can be summarized as (i) harvesting more photons in the longer wavelength region to increase <i>J</i>_sc; (ii) obtaining the lower mixed highest occupied molecular orbital (HOMO) energy level by incorporating SMPV1 to increase <i>V</i>_oc; (iii) forming the better charge carrier transport channels through the cascade energy level structure and optimizing phase separation of donor/acceptor materials to increase <i>J</i>_sc and FF

Rectifying Characteristics and Semiconductor–Metal Transition Induced by Interfacial Potential in the Mn₃CuN/n-Si Intermetallic Heterojunction

The Mn₃CuN/n-Si heterojunction device is first designed in the antiperovskite compound, and excellent rectifying characteristics are obtained. The rectification ratio (RR) reaches as large as 38.9 at 10 V, and the open-circuit voltage <i>V</i>_oc of 1.13 V is observed under temperature of 410 K. The rectifying behaviors can be well described by the Shockley equation, indicating the existence of a Schottky diode. Simultaneously, a particular semiconductor–metal transition (SMT) behavior at 250 K is also observed in the Mn₃CuN/n-Si heterojunction. The interfacial band bending induced inversion layer, which is clarified by the interfacial schematic band diagrams, is believed to be responsible for the SMT and rectifying effects. This study can develop a new class of materials for heterojunction, rectifying devices, and SMT behaviors