Semiconductors group

Abstract:

Dataset supporting research article" "Delayed Electron-Hole Recombination in a Pseudo-Direct Semiconductor"

Abstract:

Abstract Controlling excitation transport is central to the operation of light-harvesting and light-emitting devices based on nanocrystal films. Exciton diffusion is typically described as hopping through a homogeneous medium; however, even highly monodisperse nanocrystal ensembles exhibit energetic disorder arising from size variation. We demonstrate that such disorder couples exciton diffusivity in real space to energetic relaxation within the density of states. Using spectrally and temporally resolved photoluminescence reabsorption spectroscopy of CsPbBr3 nanocrystal films, we separately track exciton diffusion and energetic relaxation across a range of temperatures and nanocrystal sizes. We find that at low temperature, excitons preferentially migrate downhill toward larger, lower-energy nanocrystals, causing a transient collapse of exciton diffusivity that is particularly pronounced for smaller nanocrystals exhibiting higher energetic disorder. At room temperature, these effects are effectively countered by thermally activated uphill transfer, restoring normal diffusion. Nanocrystal solids thus offer tunable transport properties governed by the interplay between disorder and thermal energy.

Abstract:

Reliable predictions of long-term stability are essential as halide perovskite solar cells approach widespread commercial deployment. However, extrapolation from aging tests requires knowledge of material degradation dynamics, which remain unclear for halide perovskites. Here, we reveal the structural and optoelectronic evolution of formamidinium-caesium lead-halide perovskite films under heat and/or light using in situ X-ray diffraction and photoluminescence. Heat and light combined induce much faster degradation than either stressor alone, with 1 sun illumination degrading material 53 times faster at 85 °C than room temperature. For all compositions investigated the degradation rate is highly nonlinear in time and follows a sigmoidal decay, suggestive of interface-driven dynamics. Degradation proceeds in three steps: halide segregation (for mixed-halide perovskites), A-site cation diffusion triggered by heterogeneity and strain, and finally iodine and formamidinium loss. Our findings provide a quantitative framework for lifetime predictions and highlight the necessity of combined heat and light ageing tests.

Abstract:

We investigate the impact of employing fullerene self-assembled monolayers (SAMs) in conjunction with SnO2 electron-transport layers (ETLs) in negative–intrinsic–positive (n–i–p) perovskite solar cells. We compare the efficacy of the fullerene-SAM surface-binding group—carboxylic or phosphonic acid—on the passivation, charge transport, and energetics of the modified-SnO2 surface. Planar n–i–p perovskite solar cells with these SAM-modified SnO2 exhibit significantly reduced hysteresis, and the steady-state maximum power point tracked efficiencies (η MPP) of the devices improved from an average of 18.6–20.0% comparing devices with neat SnO2 to the C60-PA SAM inclusion, respectively. While C60-PA SAM improved the initial solar cell efficiency, this benefit was not maintained during light exposure at elevated temperatures as the fullerene SAM weakened adhesion at the perovskite/metal oxide interface in the aged devices. These results highlight the importance of improving the mechanical robustness of perovskite/charge-transport layer interfaces under operational aging conditions.

Abstract:

Electrophoretic deposition (EPD) offers a scalable, solution-processable and binder-free route for assembling functional electrode films, yet its applicability across chemically diverse materials remains largely unexplored. In this study, we present a facile EPD platform for the rapid fabrication of electrodes and photoelectrodes from more than 20 functional materials, including carbon nanostructures, polymeric semiconductors, metal oxides, chalcogenides, nitrides, porous metal-organic frameworks, covalent organic frameworks and hybrid composites. Optimised deposition recipes are established for each material by controlling suspension chemistry, charging agents, applied voltage and deposition time. For photoactive materials, the photocurrent response is used as a practical descriptor to evaluate film quality and guide loading optimisation. Structural characterisation by scanning electron microscopy and transmission electron microscopy confirms uniform coatings, controlled morphologies, and intimate contact between deposited materials and conductive substrates. The versatility of the method is further validated by conformal deposition on both indium tin oxide (ITO) and porous carbon paper substrates, highlighting its compatibility with diverse electrode architectures. We also clarify the role of iodine and citric acid as charging agents for stabilising suspensions and ensuring reproducible deposition. Overall, this work demonstrates EPD as a versatile and scalable approach for integrating a wide range of functional materials into binder-free electrodes for photoelectrochemical and catalytic applications.