A nitrogen-doped graphene/sulfur composite was further modified with atomic layers of TiO2and used as the cathode of lithium–sulfur batteries, exhibiting superior cycling stability, good rate capability and high coulombic efficiency.

Atomic layer deposition (ALD) was applied to deposit ZnO on graphene aerogel, and this composite was used as an anode material for lithium ion batteries. This electrode material was further modified by an ultrathin Al2O3 layer via ALD to stabilize its electrochemical stability. These two metal oxides were uniformly immobilized on graphene frameworks, and the Al2O3 coating strongly improved the electrochemical performances of ZnO-graphene aerogel composite anodes. Particularly, the composite with 10 ALD cycles of Al2O3 coating (denoted as ZnO-G-10) exhibited a high initial discharge capacity of 1513 mA h g(-1) and maintained a reversible capacity of 490 mA h g(-1) after 100 cycles at a current density of 100 mA g(-1). Furthermore, the capacity retention rate increased from 70% to 90% in comparison with its uncoated counterpart after 100 cycles. The ZnO-G-10 anode also showed good rate-capability, delivering a discharge capacity of 415 mA h g(-1) at 1000 mA g(-1). The improved electrochemical performance is attributed to the formation of an artificial solid electrolyte interphase layer, stabilizing ZnO and the electrolyte by preventing the aggregation of Zn/ZnO nanograins and the side reaction that would cause the degradation of anodes.

The recently developed planar architecture (ITO/ZnO/PbS-TBAI/PbS-EDT/Au) has greatly improved the power conversion efficiency of colloidal quantum dot photovoltaics (QDPVs). However, the performance is still far below the theoretical expectations and trap states in the PbS-TBAI film are believed to be the major origin, characterization and understanding of the traps are highly demanded to develop strategies for continued performance improvement. Here employing impedance spectroscopy we detect trap states in the planar PbS QDPVs. We determined a trap state of about 0.34 eV below the conduction band with a density of around 3.2 × 10 16 cm −3 eV −1 . Temperature dependent open-circuit voltage analysis, temperature dependent diode property analysis and temperature dependent build-in potential analysis consistently denotes an below-bandgap activation energy of about 1.17-1.20 eV.PbS colloidal quantum dots (PbS QDs) are attractive materials for next generation photovoltaic devices due to their facile solution processing, low material cost, long term air stability and possibility of tailoring their optoelectronic properties by tuning size, composition and surface chemistry 1-4 . However, PbS QDs in solution are typically surrounded by long aliphatic ligands and once they form solid film, the long ligands act as barriers for charge transfer and transport between neighboring QDs 5-7 . The ligand-exchange procedure, which is used to remove such long ligands can create many surface traps such as vacancies and dangling bonds 8,9 , these traps assist carrier recombination, and hence seriously limit the device performance 10,11 . Great efforts have been put in developing surface passivation approaches to reduce the traps, and power conversion efficiency (PCE) of PbS quantum dot photovoltaics (QDPVs) has been significantly improved (over 10%) [12][13][14][15] . Nevertheless, the achieved PCE is still far below the expected and the surface traps remains a key limiting factor for PbS QDPVs [16][17][18] .Trap states in the PbS QDPVs has been carefully investigated to understand how they limit the device performance. Here we employ Impedance Spectroscopy (IS) to obtain the information of the trap states in our fabricated device with currently most advanced architecture of ITO/ZnO/PbS-TBAI/PbS-EDT/Au (shown in Fig. 1(a)) 12,13 . In such a device the diode property is from ZnO/PbS-TBAI heterojunction, and the PbS-EDT layer acts as an electron-blocking layer between the PbS-TBAI layer and the Au anode 24 . For the ZnO/PbS-TBAI heterojunction, after suitable illumination (mainly for the UV region), the ZnO doping density is much higher than the PbS-TBAI doping density, thereby can be regarded as a N + P abrupt junction, with the depletion region locates in the PbS-TBAI film 25,26 . In our study we use AM 1.5 illumination (10 min AM 1.5 illumination) to generate a N + P ZnO/PbS-TBAI heterojunction, and then performed various measurements including current-voltage and capacitance-voltage under various temperatures to gain information in...

A reduced graphene oxide (rGO)-sulfur composite aerogel with a compact self-assembled rGO skin was further modified by an atomic layer deposition (ALD) of ZnO or MgO layer, and used as a free-standing electrode material of a lithium-sulfur (Li-S) battery. The rGO skin and ALD-oxide coating worked as natural and artificial barriers to constrain the polysulfides within the cathode region. As a result, the Li-S battery based on this electrode material exhibited superior cycling stability, good rate capability and high coulombic efficiency. Furthermore, ALD-ZnO coating was tested for performance improvement and found to be more effective than ALD-MgO coating. The ZnO modified G-S electrode with 55 wt% sulfur loading delivered a maximum discharge capacity of 998 mA h g(-1) at a current density of 0.2 C. A high capacity of 846 mA h g(-1) was achieved after charging/discharging for 100 cycles with a coulombic efficiency of over 92%. In the case of using LiNO3 as a shuttle inhibitor, this electrode showed an initial discharge capacity of 796 mA h g(-1) and a capacity retention of 81% after 250 cycles at a current density of 1 C with an average coulombic efficiency higher than 99.7%.