Star-shaped fluorene-BODIPY oligomers: versatile donor-acceptor systems for luminescent solar concentrators

Energy transfer in star-shaped donor–acceptor molecules reduces self-absorption in luminescent solar concentrators.N. J. L. K. D. is supported by the Cambridge Commonwealth European and International Trust, Cambridge Australian Scholarships and Mr Charles K Allen. R. W. M. acknowledges funding from the Initiative and Networking Fund of the Helmholtz Association. S. T. E. J. is supported by the Royal society. RGDT is supported by the EPSRC. D. C. thanks the Royal Society. PJS thanks the Royal Society for a Wolfson Research Merit Award. This work as supported by the EPSRC [EP/M005143/1, EP/M014797/1, EP/L012200/1]

Photon Reabsorption in Mixed CsPbCl3_{3}:CsPbI3_{3} Perovskite Nanocrystal Films for Light-Emitting Diodes

Cesium lead halide nanocrystals, CsPbX$_{3}$ (X = Cl, Br, I), exhibit photoluminescence quantum efficiencies approaching 100% without the core-shell structures usually used in conventional semiconductor nanocrystals. These high photoluminescence efficiencies make these crystals ideal candidates for light-emitting diodes (LEDs). However, because of the large surface area to volume ratio, halogen exchange between perovskite nanocrystals of different compositions occurs rapidly, which is one of the limiting factors for white-light applications requiring a mixture of different crystal compositions to achieve a broad emission spectrum. Here, we use mixtures of chloride and iodide CsPbX$_{3}$ (X = Cl, I) perovskite nanocrystals where anion exchange is significantly reduced. We investigate samples containing mixtures of perovskite nanocrystals with different compositions and study the resulting optical and electrical interactions. We report excitation transfer from CsPbCl$_{3}$ to CsPbI$_{3}$ in solution and within a poly(methyl methacrylate) matrix via photon reabsorption, which also occurs in electrically excited crystals in bulk heterojunction LEDs.N.J.L.K.D. thanks the Cambridge Commonwealth European and International Trust, Cambridge Australian Scholarships, and Charles K. Allen for financial support. M.T. thanks the Gates Cambridge Trust, EPSRC, and the Winton Programme for the Physics of Sustainability for financial support. J.R. thanks the Cambridge Commonwealth European and International Trust, EPSRC and the Winton Programme for the Physics of Sustainability for financial support. E.P.B. thanks the EPSRC Centre for Doctoral Training: New and Sustainable Photovoltaics. R.D.L. thanks the EPSRC for funding. S.M.M. acknowledges competitive research funding from King Abdullah University of Science and Technology (KAUST). F.W.R.R. gratefully thanks financial support from CNPq Grant No. 246050/2012-8. F.W.R.R. and C.D. acknowledge funding from the ERC under Grant No. 259619 PHOTO-EM. C.D. acknowledges financial support from the EU under Grant No. 312483 ESTEEM2. F.D. is thankful for the Herchel Smith fellowship. This work was supported by the EPSRC (Grant Nos. EP/M005143/1, EP/G060738/1, and EP/G037221/1)

Optimisation of pH of cadmium chloride post-growth-treatment in processing CDS/CDTE based thin film solar cells

The role of Chlorine-based activation in the production of high quality CdS/CdTe photovoltaic have been well discussed and explored with an overlook of the effect of Cadmium chloride (CdCl2) post-growth treatment acidity on the property of the fabricated devices. This work focuses on the optimisation of CdCl2 post-growth treatment pH as it affects both the material and fabricated device properties of all-electrodeposited multilayer glass/FTO/n-CdS/n-CdTe/p-CdTe configuration. CdCl2 treatments with acidity ranging from pH1 to pH4 were explored. The properties of the ensued CdTe layer were explored using optical, morphological, compositional structural and electrical property analysis, while, the effect on fabricated multilayer glass/FTO/n-CdS/n-CdTe/p-CdTe configuration were also explored using both I-V and C-V measurements. Highest improvements in the optical, morphological, compositional and structural were observed at pH2 CdCl2 post-growth treatment with an improvement in absorption edge, grain size, crystallinity and crystallite size. Conductivity type conversions from n-CdTe to p-CdTe, increase in pin-hole density and collapse of the absorption edge were observed after pH1 CdCl2 treatment. The highest fabricated solar cell efficiency of 13% was achieved using pH2 CdCl2 treatment as compared to other pH values explored

Simple and Robust Panchromatic Light Harvesting Antenna Composites via FRET Engineering in Solid State Host Matrices

The efficient harvesting of incident solar radiation is an important technical challenge for future world energy and chemical needs. Luminescent solar concentrators (LSCs) can efficiently harvest solar energy and concentrate it towards a useful output, such as photovoltaic cells or a photocatalytic reactor. LSCs are planar waveguides doped with luminescent materials that emit light into waveguide modes concentrating it towards the edges. However, large scale LSCs have been limited by the reabsorption of emitted photons. To overcome this, research has turned towards creating artificial light-harvesting systems that spatially and spectrally concentrate light through different donor and acceptor chromophores. Usually these chromophores are covalently linked and synthetically complex. We report a simple, versatile and highly efficient light-harvesting antenna system consisting of dyes suspended in a PMMA micro-powder. These composites absorb light throughout the visible region of the solar spectrum, efficiently funnel the energy via FRET and then re-emits it in the deep red with PLQY >95%. These composites are extremely robust and easy to process and can be incorporated into a variety of host matrices for applications. This system is characterised via continuous wave and transient spectroscopy. Proof-of-concept-devices and simulations show it to be well suited for use in LSCs.R.P. and A.R acknowledge funding from the EPSRC and the Winton Program for the Physics of sustainability. R.W.M. acknowledges funding from the Initiative and Networking Fund of the Helmholtz Association. N.J.L.K.D. thanks the Ernest Oppenhimer Trust for a research fellowship. We thank Mustafa Calgar for assistance with SEM measurements

Excimer Formation in Carboxylic Acid-Functionalized Perylene Diimides Attached to Silicon Dioxide Nanoparticles

The creation of artificial light-harvesting complexes involves the ordered arrangement of chromophores in space. To guarantee efficient energy-transfer processes, organic dyes must be brought into close proximity, often leading to aggregation and the formation of excimer states. In recent years, the attachment of ligand-based chromophores to nanoparticles has also generated interest in relation to improved solar harvesting and spin-dependent electronic interactions such as singlet fission and upconversion. We explore the covalent attachment of two novel perylene-diimide (PDI) carboxylic acid ligands to silicon dioxide nanoparticles. This allows us to study electronic interactions between the ligands when attached to nanoparticles because these cannot couple to the wide band gap silicon dioxide. One of the synthesized PDI ligands has sterically hindering phenols in the bay position and undergoes minimal optical changes upon attachment, but the other forms an excimer state with a red-shifted and long-lived florescence. As such, molecular structure changes offer a method to tune weak and strong interactions between ligand layers on nanocrystal surfaces

Effect of Size on the Luminescent Efficiency of Perovskite Nanocrystals

ERC, the Ernest Oppenhimer Trust, CONACYT