Modulation doping of absorbent cotton derived carbon dots for quantum dot-sensitized solar cells.

In order to improve the power conversion efficiency (PCE) of quantum dot-sensitized solar cells (QDSC), a series of absorbent cotton derived carbon quantum dots (CQDs) with different dopants (namely carbamide, thiourea, and 1,3-diaminopropane) have been successfully synthesized by a one-pot hydrothermal method. The average particle sizes of the three doped CQDs are 1.7 nm, 5.6 nm, and 1.4 nm respectively, smaller than that of the undoped ones (24.2 nm). The morphological and structural characteristics of the four CQDs have been studied in detail. In addition, the three doped CQDs exhibit better optical properties compared with the undoped ones in the UV-vis and PL spectra. Then CQD-based QDSC are experimentally fabricated, showing that the short current density (Jsc) and open circuit voltage (Voc) of the QDSC are distinctly improved owing to the dopants. Especially the QDSC with the 1,3-diaminopropane doped CQD achieves the highest PCE (0.527%), 299% larger than that without dopant (0.176%). In order to highlight a reasonable mechanism, the UV-vis diffuse reflectance spectrum of CQD sensitized TiO2 and the calculated energy band structures of various CQDs are investigated. It's found from the above analysis that the addition of carbamide, thiourea, and 1,3-diaminopropane is beneficial to obtain CQDs of smaller size, and with a smaller band gap and more nitrogenous or sulphureous functional groups, which enhance the light absorption performance and photo-excitation properties. The above factors are helpful to improve the Jsc of QDSC. Nitrogen, acting as a donor to the CQDs, will assist the sensitized photoanode with a higher Fermi level, resulting in a larger Voc of the QSDC. Finally this study builds the relation among the microstructure of the CQDs, three characteristics of the CQDs (namely the spectra, energy band structure and functional groups) and the photoelectric properties of the QDSC, which will provide guidance for the modulation doping of CQDs to improve the PCE of QDSC.

Nanoporous TiO2/SnO2/Poly(3,4-ethylene-dioxythiophene): Polystyrenesulfonate Composites as Efficient Counter Electrode for Dye-Sensitized Solar Cells.

A nanoporous composite film combined of conducting inorganic template (TiO2/SnO2) and conducting polymer catalyst (poly(3,4-ethylenedioxythiophene):polystyrenesulfonate, PEDOT: PSS) was developed as an alternative counter electrode for dye-sensitized solar cell (DSSC) through low-temperature process. The TiO2/SnO2 template was first fabricated by coating a homogeneous TiO2 nanoparticles blended paste containing a SnCl4 aqueous solution on the conductive substrate, followed by annealing at 150 °C. The counter electrode was then completed by spin-coating the PEDOT: PSS aqueous solution into the template and drying at 80 °C. The obtained TiO2/SnO2/ PEDOT: PSS (TSP) composite film exhibits more excellent catalytic activity for the tri-iodide reduction than the pristine PEDOT: PSS film, resulting in the significant improvements in the fill factor and efficiency of the cells. The values of the fill factor and efficiency respectively increase from 0.564 and 4.79% to 0.699 and 6.54%. Noted that the photovoltaic performances of the TSP based DSSC is very similar to those of the Pt based one. The fill factor and efficiency of the later are 0.696 and 6.48%, respectively. The outstanding properties of the TSP composite film used as the counter electrode can be ascribed to its prominent synergistic effects. In the TSP composite film, the conducting TiO2 is applied as the main skeleton material with the in-situ formed SnO2 as a binder to construct a nanoporous structure for the PEDOT: PSS coating and also to provide numerous high-speed conductive paths for the electron transportation from the substrate to the PEDOT: PSS coating, and the PEDOT: PSS adhered on the TiO2/SnO2 skeleton mainly acts as the catalyst to enlarge its surface area allowing for more active sites for the tri-iodide reduction.

Enhanced electrocatalytic performance of N-doped carbon xerogels obtained through dual nitrogen doping for the oxygen reduction reaction.

The development of high efficiency and low-cost electrocatalysts for the oxygen reduction reaction (ORR) is urgently desired for many energy storage and conversion systems. Nitrogen-doped carbon xerogels (NCXs) which have been successfully applied as effective electrocatalysts for the ORR have continued to attract attention due to their competitive price and tunable surface chemistry. A new dual N-doped NCX (NCoNC) electrocatalyst is fabricated as a carbon based catalyst though a facile impregnation of peptone in a precursor and ammonia etching pyrolysis method. XPS analysis demonstrates that the NCoNC electrocatalyst not only has a high N doping amount, but also has an optimized chemical state composition of N doping, which play an important role in improving the microstructure and catalytic performance of the catalysts. XRD and HRTEM results show that the doped metal nano-particles are coated with a double carbon layer of graphene carbon (inner layer) and amorphous carbon (outer layer) forming serrated edges that facilitate the ORR process. The as-obtained NCoNC catalyst exhibits good electrocatalytic performance and excellent stability for the ORR in both acidic and alkaline environments. In particular, in alkaline electrolyte, the decrements of both the limiting current density and the half-wave potential of the NCoNC catalyst were significantly lower than those of a commercial Pt/C catalyst during accelerated aging tests. When serving as an air electrode in Zn-air batteries, the catalyst also exhibits superior catalytic performance with a peak power density of 78.2 mW cm-2 and a stable open-circuit voltage of 1.37-1.43 V. This work presents a novel tactic to regulate the microstructure and composition of carbon-based electrocatalysts by the facile and scalable dual-effect nitrogen doping method which may be conducive to promoting and developing highly efficient and promising electrocatalysts for the ORR.