Researchers from Shanghai University, Jiangsu University of Science and Technology, Chinese Academy of Sciences, Tongji University, Jilin University, Southern University of Science and Technology, University of Nottingham and Okinawa Institute of Science and Technology have developed efficient and stable perovskite light-emitting diodes (PeLEDs) with saturated blue emission, by building hydrogen-bonding networks both inside the perovskite layer and at its interface using a pair of isomeric molecules.
Over the past decade PeLEDs have grown brighter and cheaper to make, and compositional tuning has taken them across the visible spectrum, with red and green devices now matching - and in places beating - rival LED materials. Blue electroluminescence, however, has lagged badly behind, and that gap alone has kept full-color perovskite displays out of reach. The reason is structural - blue emission requires a wider bandgap, which in turn demands a higher operating voltage from the device. In a material held together by ionic bonds, that extra electrical stress aggravates the instability of the perovskite's octahedral framework, and the lattice degrades quickly. The result, until now, has been blue devices that are both dimmer and shorter-lived than their red and green counterparts.
The team's approach was to reinforce the crystal from the outside and the inside at once, using two isomers - molecules built from identical atoms arranged differently in space.
The first, O-benzylhydroxylamine hydrochloride (OBCl), was placed between the hole transport layer and the emitter. There it acts as a hydrogen-bonding donor, binding to the perovskite's inorganic framework and improving its structural stability. Its large dipole moment does a second job at the same time, lowering the hole energy barrier and easing charge injection into the emitter.
The second isomer, N-benzylhydroxylamine hydrochloride (NBCl), was mixed directly into the perovskite. Its role is to supply both acceptor and donor sites, allowing it to hydrogen-bond with the OB+ molecules at the interface and with the perovskite itself.
That dual capability is the heart of the design. Molecules used in earlier perovskite work could only donate a hydrogen atom to a bond; OBCl and NBCl can donate or accept one. The result is a denser, more interconnected web of hydrogen bonds running through the bulk and across the interface, rather than a set of isolated contacts.
There is a structural benefit as well. The OB+ interfacial molecules induce a preferential orientation in the perovskite film, and the isomeric hydrogen bonding reinforces that alignment - which improves carrier mobility and adds a further increment of material stability on top of the direct bonding effect.
The resulting devices reached external quantum efficiencies of 16.8% at 463 nm and 22.0% at 468 nm, which the team reports as state-of-the-art performance among pure- and deep-blue PeLEDs. Device stability improved significantly alongside the efficiency gains.
The team is clear about how far that stability still has to go. The devices currently operate for only a few hundred minutes - better than previous deep-blue designs, but short of what a commercial display would require. The advance is real on both efficiency and color quality; the operational lifetime remains the open problem.
Looking ahead, the researchers suggest the hydrogen-bonding strategy could also be applied to other perovskite devices including solar cells and sensors.
