Water‐Soluble Lacunary Polyoxometalates with Excellent Electron Mobilities and Hole Blocking Capabilities for High Efficiency Fluorescent and Phosphorescent Organic Light Emitting Diodes

Abstract

High performance solution‐processed fluorescent and phosphorescent organic light emitting diodes (OLEDs) are achieved by water solution processing of lacunary polyoxometalates used as novel electron injection/transport materials with excellent electron mobilities and hole blocking capabilities. Green fluorescent OLEDs using poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐(1,4‐benzo‐{2,1′,3}‐thiadiazole)] (F8BT) as the emissive layer and our polyoxometalates as electron transport/hole blocking layers give a luminous efficiency up to 6.7 lm W−1 and a current efficiency up to 14.0 cd A−1 which remained nearly stable for about 500 h of operation. In addition, blue phosphorescent OLEDs (PHOLEDs) using poly(9‐vinylcarbazole) (PVK):1,3‐bis[2‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazo‐5‐yl]benzene (OXD‐7) as a host and 10.0 wt% FIrpic as the blue dopant in the emissive layer and a polyoxometalate as electron transport material give 12.5 lm W−1 and 30.0 cd A−1 power and luminous efficiency, respectively, which are among the best performance values observed to date for all‐solution processed blue PHOLEDs. The lacunary polyoxometalates exhibit unique properties such as low electron affinity and high ionization energy (of about 3.0 and 7.5 eV, respectively) which render them as efficient electron injection/hole blocking layers and, most importantly, exceptionally high electron mobility of up to 10−2 cm2 V−1 s−1.

Efficient Solution-Processed Blue and Yellow Phosphorescent Organic Light-emitting Diodes Using Binary Blend Hosts

“…Here, we fabricated three solution-processed blue PhOLEDs with different host-guest system, which are a single host of mCP, and two binary hosts of mCP:PVK and mCP:DpAn-5BzAc, following the structure of ITO/PEDOT: PSS (40 nm)/host: 10 wt.% FIrpic [18,19] (20 nm)/TmPyPB (40 nm)/Liq (1 nm)/Al (100 nm). The mCP was selected as host in PhOLEDs for their relatively high triplet energy (ET).…”

Low Work Function Lacunary Polyoxometalates as Electron Transport Interlayers for Inverted Polymer Solar Cells of Improved Efficiency and Stability

“…[31][32][33][34][35][36][37] In addition, our group recently demonstrated the successful application of lacunary Keggin POMs, in particular the potassium sodium 11-tungstenphosphate (α-K7-xNaxPW11O39•14H2O, termed as B1-W) and the potassium sodium 11-molybdophosphate (α-K7-xNaxPMo11O39•14H2O, termed as B1-Mo), as electron injection materials in fluorescent and phosphorescent organic light emitting diodes (OLEDs). 38 These lacunary POMs exhibit a significant negative charge (equal to -7) due to the absence of one M(W,Mo)O6 octahedron from their structure and were found to exhibit exceptionally high electron mobility, up to 10 -2 cm 2 V -1 s -1 , which improved the OLED performance. 38 In this work, the lacunary POMs under study, as well as the newly introduced potassium 9-tungstenphosphate (α-K9PW9O34•16H2O, termed as B2-W), the structure of which exhibits three WO6-octahedrals less, promoting a higher negative charge (equal to -9), are inserted as effective interlayers between the TiO2 electron extraction layer and the photoactive film in PSC inverted architectures.…”

Impact of boron and indium doping on the structural, electronic and optical properties of SnO2

“…Tetragonal SnO 2 is a wide bandgap semiconductor which typically shows n-type conductivity due to the oxygen vacancies that are created during the crystallization process [1][2][3][4] . SnO 2 is commonly used for glazes [1] , polishing powder [2] , photovoltaics [3] , ανδ gas sensors [4] . Recently, SnO 2 has been demonstrated as a cathode material in Li-ion batteries [5] .…”