Novel Cerium-Based p-Dopants with Low Parasitic Absorption for Improved Organic Devices

High electrical conductivity and improved charge carrier injection enabled by molecular doping are pivotal for high-performance, energy-efficient, and stable organic optoelectronic devices. Molecular doping is a key element in device design and manufacturing of active-matrix organic light-emitting diode displays, a multi-billion dollar market. However, it is an inherent feature of state-of-the-art small molecule dopants and their charge-transfer complexes to strongly absorb in the visible and near-infrared spectral range. This parasitic effect results in absorption losses, reducing the performance in light-harvesting and light-emitting applications. Here, a novel class of vacuum-processable cerium-based p-dopants with excellent processing properties and competitive doping strength even in organic hole transport layers with low-lying valence levels is presented. A substantial reduction in parasitic absorption for layers doped by the new dopants in the visible and near-infrared range is found. The reduced polaron absorption of the dopant anions is in excellent agreement with theoretical simulations. By incorporating these dopants into near-infrared narrowband organic photodetectors, the specific detectivity can be increased by one order of magnitude compared to devices with the established dopant 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F₆-TCNNQ). The decreased parasitic absorption yields optical-microcavity-enhanced photodetectors with significantly reduced full-width at half maximum, paving the way toward more efficient and wavelength-selective infrared detectors.