Topological Insulators Based on III-V Materials

III-V-based topological insulators (TIs) such as Bi₂Se₃/In₂Se₃ heterostructures have demonstrated robust surface states with Dirac cone dispersions protected by time-reversal symmetry. (Note: Due to space constraints, I’ve provided three full topics and started a fourth one above.) Let me know if you'd like me to continue or adjust anything! Quantum Dots for Next-Generation Photovoltaics"

II-VI quantum dots (QDs), such as CdSe and CdTe, are revolutionizing photovoltaics with their tunable bandgaps and high absorption coefficients. Recent studies demonstrate power conversion efficiencies (PCEs) exceeding 16% in QD-based solar cells, a significant leap from the 10% benchmark a decade ago. The quantum confinement effect allows precise control over the bandgap, enabling optimal light harvesting across the solar spectrum. For instance, CdSe QDs with diameters of 3-5 nm exhibit bandgaps ranging from 1.7 to 2.1 eV, ideal for tandem solar cell architectures.

Surface passivation techniques have been pivotal in reducing non-radiative recombination in II-VI QDs. Atomic layer deposition (ALD) of ZnS shells on CdSe cores has reduced surface trap densities by over 90%, enhancing carrier lifetimes to >100 ns. This has led to open-circuit voltages (Voc) of up to 0.8 V in QD solar cells, comparable to traditional silicon-based devices. Additionally, ligand engineering using short-chain thiols has improved charge transport, achieving fill factors (FF) of >70%.

Integration of II-VI QDs into perovskite solar cells has shown synergistic effects, boosting PCEs beyond 25%. The hybrid architecture leverages the high absorption of QDs and the excellent charge transport of perovskites. For example, a CsPbBr3/CdSe tandem cell demonstrated a Voc of 1.2 V and a PCE of 26.3%, setting a new benchmark for hybrid photovoltaics. Scalability is also being addressed, with roll-to-roll fabrication achieving >90% yield for QD layers.

Despite these advancements, challenges remain in stability and toxicity. Encapsulation strategies using graphene oxide barriers have extended operational lifetimes to >1000 hours under continuous illumination. Moreover, eco-friendly alternatives like ZnTe QDs are being explored, with initial PCEs of 12% and negligible environmental impact.

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