Quantum-dot-sensitized solar cell (QDSSC) has been considered as an alternative to new generation photovoltaics, but it still presents very low power conversion efficiency. Besides the continuous effort on improving photoanodes and electrolytes, the focused investigation on charge transfer at interfaces and the rational design for counter electrodes (CEs) are recently receiving much attention. Herein, core-shell nanowire arrays with tin-doped indium oxide (ITO) nanowire core and Cu2S nanocrystal shell (ITO@Cu2S) were dedicatedly designed and fabricated as new efficient CEs for QDSSCs in order to improve charge collection and transport and to avoid the intrinsic issue of copper dissolution in popular and most efficient Cu/Cu2S CEs. The high-quality tunnel junctions formed between n-type ITO nanowires and p-type Cu2S nanocrystals led to the considerable decrease in sheet resistance and charge transfer resistance and thus facilitated the electron transport during the operation of QDSSCs. The three-dimensional structure of nanowire arrays provided high surface area for more active catalytic sites and easy accessibility for an electrolyte. As a result, the power conversion efficiency of QDSSCs with the designed ITO@Cu2S CEs increased by 84.5 and 33.5% compared to that with planar Au and Cu2S CEs, respectively.
Single-crystalline
Ni-rich cathodes with high capacity have drawn
much attention for mitigating cycling and safety crisis of their polycrystalline
analogues. However, planar gliding and intragranular cracking tend
to occur in single crystals with cycling, which undermine cathode
integrity and therefore cause capacity degradation. Herein, we intensively
investigate the origin and evolution of the gliding phenomenon in
single-crystalline Ni-rich cathodes. Discrete or continuous gliding
forms are revealed with new surface exposure including the gliding
plane (003) and reconstructed (−108) under surface energy drive.
It is also demonstrated that the gliding process is the in-plane migration
of transition metal ions, and reducing oxygen vacancies will increase
the migration energy barrier by which gliding and microcracking can
be restrained. The designed cathode with less oxygen deficiency exhibits
outstanding cycling performance with an 80.8% capacity retention after
1000 cycles in pouch cells. Our findings provide an insight into the
relationship between defect control and chemomechanical properties
of single-crystalline Ni-rich cathodes.
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