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Perovskite solar cell (PSCs) technology has made a tremendous impact in the solar cell community due to the exceptional performance of PSCs as the power conversion efficiency (PCE) surged to a world record of 22% within the last few years. Despite this high efficiency value, the commercialization of PSCs for large area applications at affordable prices is still pending due to the low stability of the devices under ambient atmospheric conditions and the very high cost of the hole transporting materials (HTMs) used as the charge transporting layer in these devices. To cope with these challenges, the use of cheap HTMs can play a dual role in terms of lowering the overall cost of perovskite technology as well as protecting the perovskite layer to achieve a higher stability. To achieve these goals, various new organic hole transporting materials (HTMs) have been proposed. In this study, we used a unique and novel anthanthrone (ANT) dye as a conjugated core building block and an affordable moiety to synthesize a new HTM. The commercially available dye was functionalized with an extended diphenylamine (DPA) end capping group. The newly developed HTM, named DPA–ANT–DPA, was synthesized in a single step and used successfully in mesoporous perovskite solar cell devices, achieving a PCE of 11.5% under 1 Sun condition with impressive stability. The obtained device efficiency is amongst the highest as compared to that of other D–A–D molecular design and low band gap devices. This kind of low cost HTM based on an inexpensive starting precursor, anthanthrone dye, paves the way for the economical and large-scale production of stable perovskite solar cells. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are considered promising for a large range of emerging technologies ranging from advanced electronics to utilization as nanoreactors. Here we report a controlled facile synthesis of aligned carbon nanotubes with very small dimensions directly grown on steel grid substrates via two-step catalytic chemical vapor deposition (CCVD) of a molecular catalyst (ferrocene) with ethylene as the carbon source. The system is characterized by resonance Raman spectroscopy and the results show single walled carbon nanotube (SWCNT) arrays composed of 0.80 nm to 1.24 nm semiconducting CNTs, as analyzed using Kataura analysis, which is approaching the lowest diameters attainable for SWCNTs. The G+ and G− mode splitting, G− line shapes and ring breathing modes (RBMs) are analyzed to characterize the CNTs. The approach results in close packed and vertically aligned SWCNT bundles formed into hair shapes, with some contribution from multiwall CNTs (MWCNTs). IR spectroscopy is utilized to characterize the edge/defect states that have the ability to form esters and ether bonds in the as-prepared CNTs. The stepwise deposition of the catalyst followed by the carbon source gives control over the formation of small diameter single walled carbon nanotubes (SWCNTs). The utilization of molecular catalysts for narrow diameter growth directly on steel grid substrates forms a promising approach for producing cost-effective CNT substrates for a plethora of sensing and catalytic applications. [ABSTRACT FROM AUTHOR]

The formation of CH3NH3PbI3 (MAPbI3) from its precursors is probably the most significant step in the control of the quality of this semiconductor perovskite material, which is highly promising for photovoltaic applications. Here we investigated the transformation of spin coated PbI2 films to MAPbI3 using a reaction with MAI in vapor phase, referred to as vapor assisted solution process (VASP). The presence of a mesoporous TiO2 scaffold on the substrate was found to speed up reaction and led to complete conversion of PbI2, while reaction on glass substrates was slower, with some PbI2 remaining even after prolonged reaction time. Based on data from UV-visible spectroscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, the formation of an X-ray amorphous intermediate phase is proposed, which is identified by an increasing absorption from 650 to 500 nm in the absorption spectrum. This feature disappears upon long reaction times for films on planar substrates, but persists for films on mesoporous TiO2. Poor solar cell performance of planar VASP prepared devices was ascribed to PbI2 remaining in the film, forming a barrier between the perovskite layer and the compact TiO2/FTO contact. Good performance, with efficiencies up to 13.3%, was obtained for VASP prepared devices on mesoporous TiO2. [ABSTRACT FROM AUTHOR]

The interaction of acetylene with TiO2 (Evonik P25) was studied as a function of gas pressure and contact time by in situ vibrational (infrared and Raman) and electronic (UV-vis) spectroscopy and by gas chromatography-mass spectrometry analysis (GC-MS) of the reaction products. At low pressure the reaction proceeds through surface adsorption of acetylene and cyclotrimerization to benzene. At higher pressure (P > 100 mbar) the adsorption step is followed by the progressive formation of more complex oligomerization products containing an increasing number of conjugated double bonds. The final products obtained after mild heating at 373 K in acetylene excess absorb in the visible spectral region and confer to the system a strong blue color. These colored species are stable for many days in pure oxygen or air and cannot be extracted with common solvents, appearing strongly anchored to the TiO2 surface. The formation of saturated -CH3 and -CH2 groups during the oligomerization process and the spectroscopic and GC-MS results show that the colored species consist of polycyclic aromatic hydrocarbons containing a considerable number of condensed rings. Following these results, the controlled oligomerization of acetylene can represent a route for direct production of graphene-like species tightly anchored to the TiO2 surface, i.e. of composite materials of potential interest in photocatalysis or photovoltaic applications. [ABSTRACT FROM AUTHOR]