Direct comparison between perovskite-structured hybrid organic-inorganic methylammonium lead bromide (MAPbBr3) and all-inorganic cesium lead bromide (CsPbBr3), allows identifying possible fundamental differences in their structural, thermal and electronic characteristics. Both materials possess a similar direct optical band gap, but CsPbBr3 demonstrates a higher thermal stability than MAPbBr3. In order to compare device properties, we fabricated solar cells, with similarly synthesized MAPbBr3 or CsPbBr3, over mesoporous titania scaffolds. Both cell types demonstrated comparable photovoltaic performances under AM1.5 illumination, reaching power conversion efficiencies of ∼6% with a poly aryl amine-based derivative as hole transport material. Further analysis shows that Cs-based devices are as efficient as, and more stable than methylammonium-based ones, after aging (storing the cells for 2 weeks in a dry (relative humidity 15-20%) air atmosphere in the dark) for 2 weeks, under constant illumination (at maximum power), and under electron beam irradiation.

Cesium lead bromide (CsPbBr 3) was recently introduced as a potentially high performance thin-film halide perovskite (HaP) material for optoelectronics, including photovoltaics, significantly more stable than MAPbBr 3 (MA=CH 3 NH 3 +). Because of the importance of single crystals to study relevant material properties per se, crystals grown under conditions comparable to those used for preparing thin films, i.e. low-temperature solution-based growth, are needed. We show here two simple ways: anti-solvent-vapor saturation or heating a solution containing retrograde soluble CsPbBr 3 , to grow single crystals of CsPbBr 3 from a precursorsolution, treated with acetonitrile (MeCN) or methanol (MeOH). The precursor solutions are stable for at least several months. Millimeter-sized crystals are grown without crystal-seeding and can provide a 100% yield of CsPbBr 3 perovskite crystals, avoiding a CsBr-rich (or PbBr 2rich) composition, which is often present alongside the perovskite phase. Further growth has been demonstrated to be possible with crystal-seeding. The crystals are characterized in several ways, including first results of charge carrier lifetime (30 ns) and an upper-limit of the Urbach energy (19 meV). As the crystals are grown from a polar solvent (DMSO), which is similar to those used to grow hybrid organic-inorganic HaP crystals, this may allow growing mixed (organic and inorganic) monovalent cation HaP crystals.

Solar cells based on “halide perovskites” (HaPs) have demonstrated unprecedented high power conversion efficiencies in recent years. However, the well-known toxicity of lead (Pb), which is used in the most studied cells, may affect its widespread use. We explored an all-inorganic lead-free perovskite option, cesium tin bromide (CsSnBr3), for optoelectronic applications. CsSnBr3-based solar cells exhibited photoconversion efficiencies (PCEs) of 2.1%, with a short-circuit current (J SC) of ∼9 mA cm–2, an open circuit potential (V OC) of 0.41 V, and a fill factor (FF) of 58% under 1 sun (100 mW cm–2) illumination, which, even though meager compared to the Pb analogue-based cells, are among the best reported until now. As reported earlier, addition of tin fluoride (SnF2) was found to be beneficial for obtaining good device performance, possibly due to reduction of the background carrier density by neutralizing traps, possibly via filling of cation vacancies. The roles of SnF2 on the properties of the CsSnBr3 were investigated using ultraviolet photoemission spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analysis.

Lead-based halide perovskites (APbX3) are fascinating optoelectronic materials. Because of toxicity issues of Pb, Sn-based halide perovskites are studied, although less so, as an alternative. Adding SnF2 often improves the properties of Sn halide perovskite-based devices. This effect is usually ascribed to suppression of Sn2+ → Sn4+ oxidation and/or decreased Sn vacancy concentration. These effects will change the doping, sometimes in opposite directions. Here we review the effect of addition of SnF2 during the formation of ASnX3 layers as observed by different groups, both to the properties of the layers themselves and to photovoltaic cells made from these layers. SnF2 can affect many different properties of the ASnX3 perovskites, including film morphology, doping, control over formation of unwanted crystal phases, material stability to various factors, and energy level positions. It also improves (in general) the performance of photovoltaic cells made with these layers. Besides focusing on all these issues, we also describe possible doping scenarios for the perovskites, including some that do not appear to have been considered before and conclude that the doping mechanism depends strongly on whether the oxidation of Sn2+ to Sn4+ occurs during the materials preparation or after the film is formed, and if oxygen is involved.

A novel, inexpensive biofunctionalization approach is adopted to develop a multimodal and theranostic nanoagent, which combines cancer-targeted magnetic resonance/optical imaging and pH-sensitive drug release into one system. This multifunctional nanosystem, based on an ultrasmall superparamagnetic iron oxide (USPIO) nanocore, is modified with a hydrophilic, biocompatible, and biodegradable coating of N-phosphonomethyl iminodiacetic acid (PMIDA). Using appropriate spacers, functional molecules, such as rhodamine B isothiocyanate, folic acid, and methotrexate, are coupled to the amine-derivatized USPIO-PMIDA support with the aim of endowing simultaneous targeting, imaging, and intracellular drug-delivering capability. For the first time, phosphonic acid chemistry is successfully exploited to develop a stealth, multifunctional nanoprobe that can selectively target, detect, and kill cancer cells overexpressing the folate receptor, while allowing real-time monitoring of tumor response to drug treatment through dual-modal fluorescence and magnetic resonance imaging.