Colloidal CsPbX3 (X = Cl, Br, and I) nanocrystals have recently emerged as preferred materials for light-emitting diodes, along with opportunities for photovoltaic applications. Such applications rely on the nature of valence and conduction band edges and optical transitions across these edges. Here we elucidate how halide compositions control both of these correlated parameters of CsPbX3 nanocrystals. Cyclic voltammetry shows that the valence band maximum (VBM) shifts significantly to higher energies by 0.80 eV, from X = Cl to Br to I, whereas the shift in the conduction band minimum (CBM) is small (0.19 eV) but systematic. Halides contribute more to the VBM, but their contribution to the CBM is also not negligible. Excitonic transition probabilities for both absorption and emission of visible light decrease probably because of the increasing dielectric constant from X = Cl to Br to I. These band edge properties will help design suitable interfaces in both devices and heterostructured nanocrystals.

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Colloidal all inorganic CsPbX (X = Cl, Br, I) nanocrystals (NCs) have emerged to be an excellent material for applications in light emission, photovoltaics, and photocatalysis. Efficient interfacial transfer of photogenerated electrons and holes are essential for a good photovoltaic and photocatalytic material. Using time-resolved terahertz spectroscopy, we have measured the kinetics of photogenerated electron and hole transfer processes in CsPbBr NCs in the presence of benzoquinone and phenothiazine molecules as electron and hole acceptors, respectively. Efficient hot electron/hole transfer with a sub-300 fs time scale is the major channel of carrier transfer thus overcomes the problem related to Auger recombination. A secondary transfer of thermalized carriers also takes place with time scales of 20-50 ps for electrons and 137-166 ps for holes. This work suggests that suitable interfaces of CsPbX NCs with electron and hole transport layers would harvest hot carriers, increasing the photovoltaic and photocatalytic efficiencies.

Cyclic voltammetry has been used to investigate the interaction between reduced graphene oxide (r-GO) and CdTe quantum dots (Q-CdTe). For that, the composite of Q-CdTe with r-GO (r-GO-CdTe) was prepared by carrying out the reduction of graphene oxide and the synthesis of Q-CdTe simultaneously, in a single bath. r-GO-CdTe was characterized by UV–visible, steady state fluorescence, time-resolved fluorescence, X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM). Cyclic voltammetry was employed to determine the quasi-particle gap and band edge parameters of Q-CdTe and r-GO-CdTe. The blue shifts in the quasi-particle gap of r-GO-CdTe have been attributed to the strong interaction of graphene with CdTe. These interactions were further verified by time-resolved fluorescence and Raman spectroscopy which suggested strong electronic coupling between Q-dots and graphene.