Oxd 7

A blend of the high-molecular weight polymer poly(9-vinylcarbazole) (PVK, M_w = 1.1 × 10⁶ g mol⁻¹, 193.24 g mol⁻¹ per repeat unit, Sigma-Aldrich) and the small molecule 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene (OXD-7, 478.58 g mol⁻¹, Lumtec) in a 1:1 mass ratio was the host. Three different compounds were investigated for the guest: (i) 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN, 788.89 g mol⁻¹, Lumtec)^{22 (link)}, (ii) 2-[4-(diphenylamino) phenyl]-10,10-dioxide-9H-thioxanthen-9-one (TXO-TPA, 487.57 g mol⁻¹, Lumtec)^{28 (link)}, and (iii) 7,10-Bis(4-(diphenylamino)phenyl)-2,3-dicyanopyrazinophenanthrene (TPA-DCPP, 766.89 g mol⁻¹, Lumtec)^{51 (link)}. The electrolyte was tetrahexylammonium tetrafluoroborate (THABF₄, 217.07 g mol⁻¹, Sigma-Aldrich). All materials were used as received.
The master inks were prepared by separately dissolving the above materials in chlorobenzene in a concentration of 20 g L⁻¹ by stirring on a magnetic hot plate at 323 K for > 4 h. The active-material inks were prepared by blending the master inks in a desired mass ratio, followed by stirring on a magnetic hot plate at 323 K for > 4 h. In total, more than 45 different active-material compositions were investigated.

The chemical structure of the host materials poly(9-vinycarbazole) (PVK, Sigma-Aldrich) and 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene (OXD-7, Lumtec) are presented in the inset of Fig. 2a, b. Other investigated host compounds include the commercially available materials Triplet Host 123 (TH123, Merck) and Triplet Host 105 (TH105, Merck). A wide range of commercially available guest compounds were investigated, including tris[2-(5-substituent-phenyl)-pyridinato]iridium(III) (Ir(R-ppy)₃, Merck, see Fig. 2d), tris[2-(p-tolyl)pyridine]iridium(III) (Ir(mppy)₃, Lumtec), and tris[2-(4-n-hexylphenyl)quinoline]iridium(III) (Hex-Ir(piq)₃, Lumtec); see insets in Supplementary Fig. 4a and b. The investigated electrolytes are tetrahexylammonium tetrafluoroborate (THABF₄, Sigma-Aldrich, see Fig. 2e) and LiCF₃SO₃ (Sigma-Aldrich) dissolved in hydroxyl-capped trimethylolpropane ethoxylate (TMPE-OH, M_w = 450 g mol⁻¹, Sigma-Aldrich). All of the materials were used as received. The master solutions were prepared by dissolving the constituent material in chlorobenzene at a concentration of 15 mg ml⁻¹ (PVK), 30 mg ml⁻¹ (OXD-7), 20 mg ml⁻¹ (PVK:OXD-7), 20 mg ml⁻¹ (TH123:TH105), 10 mg ml⁻¹ (THABF₄), and 10 mg ml⁻¹ (TMPE-OH:LiCF₃SO₃). The master solutions were stirred on a magnetic hot plate at 343 K for at least 5 h before further processing.

Master inks were prepared by separately dissolving the solutes poly(9-vinycarbazole) (PVK, M_w 1.1 × 10⁶ g mol⁻¹, Sigma-Aldrich), 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene (OXD-7, Lumtec), tris[2-(5-substituent-phenyl)-pyridinato]iridium(III) (Ir(R-ppy)₃, Merck) and tetrahexylammonium tetrafluoroborate (THABF₄, Sigma-Aldrich) in either chlorobenzene (anhydrous, Sigma-Aldrich), ethoxybenzene (Sigma-Aldrich) or anisole (anhydrous, Sigma-Aldrich) under stirring on a hot plate kept at 70 °C for 5 h. The master inks were blended together in a mass ratio of PVK:OXD-7:Ir(R-ppy)₃:THABF₄ = 32.3:32.3:29.0:6.4 and a total solute concentration as described below for each solvent. The resulting active-material ink was stirred on the hot plate at 70 °C for at least 1 h before further processing. The ink preparation was performed in a N₂-filled glovebox ([O₂], [H₂O] < 1 ppm).