Colloidal nanoplatelets, quasi-two-dimensional quantum wells, have recently been introduced as colloidal semiconductor materials with the narrowest known photoluminescence line width (∼10 nm). Unfortunately, these materials have not been shown to have continuously tunable emission but rather emit at discrete wavelengths that depend strictly on atomic-layer thickness. Herein, we report a new synthesis approach that overcomes this issue: by alloying CdSe colloidal nanoplatelets with CdS, we finely tune the emission spectrum while still leveraging atomic-scale thickness control. We proceed to demonstrate light-emitting diodes with sub-bandgap turn-on voltages (2.1 V for a device emitting at 2.4 eV) and the narrowest electroluminescence spectrum (FWHM ∼12.5 nm) reported for colloidal semiconductor LEDs.

Energy level alignment between host and dopant molecules plays a critical role in exciton formation and harvesting in light emission zone of organic light-emitting diodes. Understanding the mechanism for predicting energy level alignment is thus important in materials selection for fabricating high-performance organic light-emitting devices. Here we show that host-dopant energy level alignment strongly depends on film thickness and substrate work function by using X-ray and ultraviolet photoemission spectroscopy. Invariant Gaussian density of states fails to explain the experimental data. We speculate that energy disorder in molecules next to the surface dictates the alignment. Ultraviolet photoemission spectroscopy measurements of several archetypical organic semiconductors confirm our speculation. An empirical interface disorder function is derived and used to construct a functional Gaussian density of states to compute host energy levels. Host-dopant energy level alignment is then computed by applying the universal energy alignment rule and is found in excellent agreement with the experimental data.

In the field of organic photovoltaics (OPVs), outdoor stability research has lagged behind material development and device engineering. Testing protocols established at the International Summit of OPV Stability (ISOS) have stimulated some stability research, but these studies are almost exclusively limited to already-refined devices made with already-commercialized materials. If OPV materials were tested outdoors during small-scale stages, stability issues could be detected earlier in the development cycle. Chloro−(chloro) n −boron subnaphthalocyanine (Cl−Cl n BsubNc) is a material with high OPV performance but has not previously been tested outdoors. An OPV power conversion efficiency of 8.4% has been previously demonstrated for a trilayer stack containing α-sexithiophene, Cl−Cl n BsubNc, and chloro−boron subphthalocyanine (Cl−BsubPc). Building on the most advanced ISOS outdoor testing protocols (ISOS-O3), we assess the outdoor stability of small-scale bilayer and trilayer OPVs while establishing an improved stability screening method for future derivatives. The outdoor stability of Cl−Cl n BsubNc is determined to be comparable to that of Cl−BsubPc.

Organic light-emitting diodes (OLEDs) show potential as the next-generation solidstate lighting technology. A major barrier to widespread adoption at this point is the efficiency droop that occurs for OLEDs at practical brightness (∼5000 cd∕m 2 ) levels necessary for general lighting. We highlight recent progress in highly efficient OLEDs at high brightness, where improvements are made by managing excitons in these devices through rational device design. General design principles for both white and monochrome OLEDs are discussed based on recent device architectures that have been successfully implemented. We expect that an improved understanding of exciton dynamics in OLEDs in combination with innovative device design will drive future development.