Benzophenones as Generic Host Materials for Phosphorescent Organic Light-Emitting Diodes

Despite the fact that benzophenone has traditionally served as a prototype molecular system for establishing triplet state chemistry, materials based on molecular systems containing the benzophenone moiety as an integral part have not been exploited as generic host materials in phosphorescent organic light-emitting diodes (PhOLEDs). We have designed and synthesized three novel host materials, i.e., BP2–BP4, which contain benzophenone as the active triplet sensitizing molecular component. It is shown that their high band gap (3.91–3.93 eV) as well as triplet energies (2.95–2.97 eV) permit their applicability as universal host materials for blue, green, yellow, and red phosphors. While they serve reasonably well for all types of dopants, excellent performance characteristics observed for yellow and green devices are indeed the hallmark of benzophenone-based host materials. For example, maximum external quantum efficiencies of the order of 19.2% and 17.0% were obtained from the devices fabricated with yellow and green phosphors using BP2 as the host material. White light emission, albeit with rather poor efficiencies, has been demonstrated as a proof-of-concept by fabrication of co-doped and stacked devices with blue and yellow phosphors using BP2 as the host material

Amorphous Host Materials Based on Tröger’s Base Scaffold for Application in Phosphorescent Organic Light-Emitting Diodes

Tröger’s bases (<b>TB</b>s) functionalized with carbazoles (<b>TB-Cz</b>s) and phosphine oxides (<b>TB-PO</b>s) were designed and synthesized as host materials for application in phosphorescent organic light-emitting diodes. The <b>TB</b> scaffold is shown to impart thermal stability with high <i>T</i>_g values (171–211 °C) as well as high triplet energies in the range of 2.9–3.0 eV. With a limited experimentation of the devices, it is shown that the <b>TB</b>s doped with a green phosphor, namely, Ir­(ppy)₃, permit impressive external efficiencies on the order of ca. 16% with a high brightness of ca. 3000–4000 cd/m². Better device performance results are demonstrated by a small structural manipulation of the <b>TB</b> scaffold involving substitution of methyl groups in the core scaffold

Nitrogen-Free Bifunctional Bianthryl Leads to Stable White-Light Emission in Bilayer and Multilayer OLED Devices

White organic light-emitting diodes (WOLEDs) are at the center stage of OLED research today because of their advantages in replacing the high energy-consuming lighting technologies in vogue for a long time. New materials that emit white light in simple devices are much sought after. We have developed two novel electroluminescent materials, referred to as <b>BABZF</b> and <b>BATOMe</b>, based on a twisted bianthryl core, which are brilliantly fluorescent, thermally highly stable with high <i>T</i>_d and <i>T</i>_g, and exhibit reversible redox property. Although inherently blue emissive, <b>BABZF</b> leads to white-light emission (CIE ≈ 0.28, 0.33) with a moderate power efficiency of 2.24 lm/W and a very high luminance of 15 600 cd/m² in the fabricated multilayer nondoped OLED device. This device exhibited excellent color stability over a range of applied potential. Remarkably, similar white-light emission was captured even from a double-layer device, attesting to the innate hole-transporting ability of <b>BABZF</b> despite it being non-nitrogenous, that is, lacking any traditional hole-transporting di-/triarylamino group(s). Similar studies with <b>BATOMe</b> led to inferior device performance results, thereby underscoring the importance of dibenzofuryl groups in <b>BABZF</b>. Experimental as well as theoretical studies suggest the possibility of emission from multiple species involving <b>BABZF</b> and its exciplex and electroplex in the devices. The serendipitously observed white-light emission from a double-layer device fabricated with an unconventional hole-transporting material (HTM) opens up new avenues to create new non-nitrogenous HTMs that may lead to more efficient white-light emission in simple double-layer devices

Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting

Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current–voltage (<i>I</i>–<i>V</i>) characteristics as an indicator to qualify the <i>I</i>–<i>V</i> sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications