We demonstrate the usage of the Lewis-acidic copper(II)hexafluoroacetylacetonate (Cu(hfac)2) and copper(II)trifluoroacetylacetonate (Cu(tfac)2) as low-cost p-dopants for conductivity enhancement of solution processable hole transport layers based on small molecules in organic light emitting diodes (OLEDs). The materials were clearly soluble in mixtures of environmentally friendly anisole and xylene and spin-coated under ambient atmosphere. Enhancements of two and four orders of magnitude, reaching 4.0 × 10−11 S/cm with a dopant concentration of only 2 mol% Cu(hfac)2 and 1.5 × 10−9 S/cm with 5 mol% Cu(tfac)2 in 2,2′,7,7′-tetra(N,N-ditolyl)amino-9,9-spiro-bifluorene (spiro-TTB), respectively, were achieved. Red light emitting diodes were fabricated with reduced driving voltages and enhanced current and power efficiencies (8.6 lm/W with Cu(hfac)2 and 5.6 lm/W with Cu(tfac)2) compared to the OLED with undoped spiro-TTB (3.9 lm/W). The OLED with Cu(hfac)2 doped spiro-TTB showed an over 8 times improved LT50 lifetime of 70 h at a starting luminance of 5000 cd/m2. The LT50 lifetime of the reference OLED with PEDOT:PSS was only 8 h. Both non-optimized OLEDs were operated at similar driving voltage and power efficiency.
In this work, electrochemically recyclable lithium is analyzed as high energy density, large scale storage material for stranded renewable energy in a closed loop. The strongly exothermic reaction of lithium with carbon dioxide (CO2) yields thermal energy directly comparable to the combustion of coal or methane in an oxygen containing atmosphere. The thermal level of the reaction is sufficient for re-electrification in a thermal power plant compatible process.The reaction of single lithium particles, avoiding particle-particle interactions, is compared to the combustion of atomized lithium spray in a CO2 containing atmosphere. Particle temperatures of up to 4000K were found for the reaction of single lithium particles in a CO2, nitrogen (N2), oxygen (O2) and steam gas mixture. Furthermore the combustion of atomized lithium spray in both dry CO2 atmosphere and CO2/steam gas mixture was analyzed. The identified solid reaction products are lithium carbonate, lithium oxide and lithium hydroxide. The formation of carbon monoxide (CO) as gaseous reaction product is demonstrated. Carbon monoxide is a valuable by-product, which could be converted to methanol or gasoline using hydrogen.
In this work, the exothermic reaction of the chemical energy storage material for stranded renewable energy, lithium is analyzed in carbon dioxide (CO2) and air. Spectroscopic techniques were used to characterize the reaction of bulk lithium pellets of up to 1 g weight. In comparison, power plant applicable combustion of atomized lithium spray was analyzed.Electrical high voltage spark was used to overcome to activation energy of the combustion for the experiments with bulk lithium. The lithium spray was successfully ignited by pre-heating the reaction gases (air and CO2).Radiation temperature of the bulk lithium during reaction in air was calculated to 2260 K. The observed green and red emission of the lithium combustion could be demonstrated in the spectral analysis.In CO2 atmosphere the reaction products were found to be lithium carbonate with little lithium oxide. Beside, lithium carbide could be detected in the reaction product of the combustion of bulk lithium. The gaseous reaction product carbon monoxide (CO), which could be further converted with hydrogen from renewable sources to valuable methanol or gasoline, was detected online by gas analysis.
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