Snaith group

Abstract:

Hybrid organic-inorganic perovskite solar cells have recently emerged as one of the most promising low-cost photovoltaic technologies. The remarkable progress of perovskite photovoltaics is closely related to advances in interfacial engineering and development of charge selective interlayers. Herein, we present the synthesis and characterization of a fused azapolyheteroaromatic small molecule, namely anthradi-7-azaindole (ADAI), with outstanding performance as a hole-transporting layer in perovskite solar cells with inverted architecture. Its molecular arrangement, induced by hydrogen-bond-directed self-assembly, favors a suitable morphology of the perovskite layer, reducing the effects of recombination as revealed by light intensity dependence, photoluminescence, and electroluminescence studies.

Abstract:

Alternatives to lead- and tin-based perovskites for photovoltaics and optoelectronics are sought that do not suffer from the disadvantages of toxicity and low device efficiency of present-day materials. Here we report a study of the double perovskite Cs₂TeI₆, which we have synthesized in the thin film form for the first time. Exhaustive trials concluded that spin coating CsI and TeI₄ using an antisolvent method produced uniform films, confirmed as Cs₂TeI₆ by XRD with Rietveld analysis. They were stable up to 250 °C and had an optical band gap of ∼1.5 eV, absorption coefficients of ∼6 × 10⁴ cm^-1, carrier lifetimes of ∼2.6 ns (unpassivated 200 nm film), a work function of 4.95 eV, and a p-type surface conductivity. Vibrational modes probed by Raman and FTIR spectroscopy showed resonances qualitatively consistent with DFT Phonopy-calculated spectra, offering another route for phase confirmation. It was concluded that the material is a candidate for further study as a potential optoelectronic or photovoltaic material.

Abstract:

Abstract:

We present the synthesis of formamidinium lead tribromide (FAPbBr3) perovskite nanocrystals through a phosphine oxide route, where in comparison to more traditional syntheses oleylamine is replaced with trioctylphosphine oxide (TOPO). This route has previously been shown to be successful for the inorganic cesium lead tribromide perovskite nanocrystals. We examine the interactions between the precursors via nuclear magnetic resonance spectroscopy (NMR). We confirm the existence of an interaction between FA-oleate and TOPO and use this to guide the optimization of our synthesis. When the reaction is conducted at room temperature, we observe the formation of nanoparticles with high photoluminescence quantum yield (PLQY, ∼70%) at 2.39 eV (518 nm) with little ripening or size defocusing over time. Although we obtain narrow emission peaks, the crystals are irregular in shape—a testament to the impact of the FA-oleate:TOPO interaction. Despite a drop in PLQY in the washed solutions, films made maintain a high PLQY of ∼50% at 2.33 eV (532 nm), which is fortuitously the ideal wavelength for the green emission channel in displays, and we demonstrate 532 nm electroluminescence in light-emitting diodes with an EQE of 3.7%.

Abstract:

We analyze nucleation-controlled nanocrystal growth in a solution containing surface-binding molecular ligands, which can also nucleate compact layers on the crystal surfaces. We show that, if the critical nucleus size for ligands is larger and the nucleation barrier is lower than those for crystal atoms, the ligands nucleate faster than the atoms on relatively wide crystal facets but much slower, if at all, on narrow facets. Such competitive nucleation of ligands and atoms results in ligands covering predominantly wider facets, thus excluding them from the growth process, and acts as a selection mechanism for the growth of crystals with narrower facets, the so-called nanoplatelets. The theory is confirmed by Monte Carlo simulations and validated experimentally for CsPbBr3 nanoplatelets grown from solution. We find that the anisotropic crystal growth is controlled by the growth temperature and the strength of surface bonding for the passivating molecular ligands.