In organic photodiodes (OPDs) light is absorbed by excitons, which dissociate to generate photocurrent. Here, we demonstrate a novel type of OPD in which light is absorbed by polaritons, hybrid light-matter states. We demonstrate polariton OPDs operating in the ultra-strong coupling regime at visible and infrared wavelengths. These devices can be engineered to show narrow responsivity with a very weak angle-dependence. More importantly, they can be tuned to operate in a spectral range outside that of the bare exciton absorption. Remarkably, we show that the responsivity of a polariton OPD can be pushed to near infrared wavelengths, where few organic absorbers are available, with external quantum efficiencies exceeding those of a control OPD.

Through various triplet‐harvesting approaches, fluorescent organic light‐emitting diodes (OLEDs) that emit in the visible spectrum can now be fabricated with efficiencies rivaling those of their phosphorescent counterparts. However, achieving high efficiencies in the near‐infrared (NIR) is considerably more challenging. This is in part due to the low quantum yield of most fluorescent NIR emitters and inefficient triplet exciton harvesting in such devices. Here, fluorescent NIR OLEDs with an external quantum efficiency of 5.4% and a peak emission wavelength of 790 nm are demonstrated. The OLEDs are fabricated by combining a deep‐red host that undergoes thermally assisted delayed fluorescence with a near‐infrared cyanine dye that emits with high efficiency. The devices show nearly pure NIR emission with a NIR cut‐on wavelength of 749 nm and >90% emitted power at wavelengths above 750 nm. It is also shown that the host polarity strongly affects the device performance.

Metal halide perovskites are being increasingly explored for use in lightemitting diodes (LEDs), with achievements in efficiency and brightness charted across the spectrum. One path to further boosting the fraction of useful photons generated by injected electrical charges will be to tailor the emission patterns of devices. Here we investigate directional emission from layered metal halide perovskites. We quantify the proportion of inplane versus out-of-plane transition dipole components for a suite of layered perovskites. We find that certain perovskite single crystals have highly anisotropic emissions and up to 90% of their transition dipole in-plane. For thin films, emission anisotropy increases as the nominal layer thickness decreases and is generally greater with butylammonium cations than with phenethylammonium cations. Numerical simulations reveal that anisotropic emission from layered perovskites in thin-film LEDs may lead to external quantum efficiencies of 45%, an absolute gain of 13% over equivalent films with isotropic emitters.

Due to its high transparency and low sheet resistance, indium tin oxide (ITO) has been the material of choice for transparent anodes in organic light-emitting diodes (OLEDs). Indium tin oxide, however, is a source of outcoupling loss due to waveguiding and reduced mechanical stability on flexible/stretchable substrates due to its brittle nature. We demonstrate that highly efficient ITO-free OLEDs can be achieved using high quality silver electrodes and horizontally aligned dipole emitters to avoid plasmonic losses. Using an ultrathin Ag/MPTMS anode and a partially aligned phosphorescent emitter, we demonstrate OLEDs with 30% EQE, luminous efficiency exceeding 130 lm/W, and low leakage current. In addition, we demonstrate OLEDs with an optimized structure showing a 36.1% outcoupling efficiency. Theoretical calculations show that our approach can yield up to 48.4% outcoupling efficiency for perfect horizontal alignment, which exceeds the maximum achievable with ITO. The combination of a silver anode and a horizontal phosphorescent emitter is promising for the future design of ultra-efficient flexible OLEDs.