All-inorganic cesium lead halide (CsPbX3, X = Br(-), I(-)) perovskites could potentially provide comparable photovoltaic performance with enhanced stability compared to organic-inorganic lead halide species. However, small-bandgap cubic CsPbI3 has been difficult to study due to challenges forming CsPbI3 in the cubic phase. Here, a low-temperature procedure to form cubic CsPbI3 has been developed through a halide exchange reaction using films of sintered CsPbBr3 nanocrystals. The reaction was found to be strongly dependent upon temperature, featuring an Arrhenius relationship. Additionally, film thickness played a significant role in determining internal film structure at intermediate reaction times. Thin films (50 nm) showed only a small distribution of CsPbBrxI3-x species, while thicker films (350 nm) exhibited much broader distributions. Furthermore, internal film structure was ordered, featuring a compositional gradient within film. Transient absorption spectroscopy showed the influence of halide exchange on the excited state of the material. In thicker films, charge carriers were rapidly transferred to iodide-rich regions near the film surface within the first several picoseconds after excitation. This ultrafast vectorial charge-transfer process illustrates the potential of utilizing compositional gradients to direct charge flow in perovskite-based photovoltaics.

All inorganic cesium lead bromide (CsPbBr3) perovskite is a more stable alternative to methylammonium lead bromide (MAPbBr3) for designing high open-circuit voltage solar cells and display devices. Poor solubility of CsBr in organic solvents makes typical solution deposition methods difficult to adapt for constructing CsPbBr3 devices. Our layer-by-layer methodology, which makes use of CsPbBr3 quantum dot (QD) deposition followed by annealing, provides a convenient way to cast stable films of desired thickness. The transformation from QDs into bulk during thermal annealing arises from the resumption of nanoparticle growth and not from sintering as generally assumed. Additionally, a large loss of organic material during the annealing process is mainly from 1-octadecene left during the QD synthesis. Utilizing this deposition approach for perovskite photovoltaics is examined using typical planar architecture devices. Devices optimized to both QD spin-casting concentration and overall CsPbBr3 thickness produce champion devices that reach power conversion efficiencies of 5.5% with a V oc value of 1.4 V. The layered QD deposition demonstrates a controlled perovskite film architecture for developing efficient, high open-circuit photovoltaic devices.

Multipole strength distributions for isoscalar L ≤ 2 transitions in 28 Si have been extracted using 386-MeV inelastic α scattering at extremely forward angles, including 0• . Observed strength distributions are in good agreement with microscopic calculations for an oblate-deformed ground-state. In particular, a large peak at an excitation energy of 17.7 MeV in the isoscalar giant monopole resonance (ISGMR) strength is consistent with the calculations.

The isoscalar giant monopole resonance (ISGMR) strength distribution in 24 Mg has been determined from background-free inelastic scattering of 386-MeV α particles at extreme forward angles, including 0 • .

Energy transfer coupled with electron transfer is a convenient approach to mimic photosynthesis in light energy conversion. Better understanding of mechanistic details of energy transfer processes is important to enhance the performance of dye or quantum dot-sensitized solar cells. Energy transfer through both long-range dipole-based Förster resonance energy transfer (FRET) and short-range Dexter energy transfer (DET) mechanisms have been identified to occur between CdSe quantum dots (QDs) linked to a red-infrared-absorbing squaraine dye through a short thiol functional group (SQSH). Solutions of SQSH linked to CdSe were investigated through steady-state and time-resolved spectroscopy experiments to explore both mechanisms. Photoluminescence studies revealed that smaller QDs had higher energy transfer efficiencies than predicted by FRET, and femtosecond transient absorption experiments revealed faster energy transfer rates in smaller donor QD sizes. These findings supported a DET process dominating at small donor sizes. The presence of both processes illustrates multiple strategies for utilizing energy transfer in light-harvesting assemblies and the required considerations in device design to maximize energy transfer gains through either mechanism.