A light-emitting polymer developed at ETH Zurich can serve as its own photoresist, allowing fluorescent features as narrow as 110 nanometres while surviving the chemistry needed to add other colours. The result, published in Nature on September 16, links the fine patterning used for silicon chips with organic emitters that have usually required a separate, coarser process. [1]
An organic light-emitting diode, or OLED, produces light in a thin organic layer when current passes through it. A photoresist is the light-sensitive material that lets a manufacturer expose a pattern, wash away selected areas and build the next layer in alignment. Conventional OLED emitters are easily damaged by the solvents and developers in that sequence. Fine metal masks and inkjet printing avoid direct photolithography, but the paper identifies their resolution and overlay accuracy as barriers to dense integration with silicon electronics. [1]
The new material combines both jobs in one star-shaped polymer. A delayed-fluorescence emitter sits at the centre, a host shell protects it, and crosslinkable groups occupy the outer ends. The researchers spin-coated the polymer, removed residual solvent, exposed selected regions to 365-nanometre ultraviolet light or an electron beam, and rinsed the film with toluene. Exposure joins neighbouring outer groups into an insoluble network, so the unexposed material washes away while the emissive core remains active. [1] [2]
The two exposure methods established different scales. Ultraviolet patterning produced line-and-space features of 4 and 2 micrometres in a 36-nanometre film, then supported three consecutive red, green and blue patterning cycles. Electron-beam lithography produced 110- and 160-nanometre line-and-space pitches and a two-colour fluorescent image with individual features down to 200 nanometres. These are fluorescent test patterns rather than electrically driven 110-nanometre display pixels. [1] [3]
For an electrically driven device, the ultraviolet-patterned green material reached a peak external quantum efficiency of 13.3%, meaning that about 13 photons emerged for every 100 charges supplied at the best operating point. The paper compares that internal result with earlier directly patternable organic emitters that remained below 2%. The team also formed red, green and blue 30-micrometre pixels through three lithography cycles and lit the resulting 'ETH' array at 6 volts. This laboratory device is not a comparison with a commercial microdisplay production line. [1] [3]
Lifetime is the immediate constraint. After reducing residual copper and changing transport layers, the crosslinked green device took 146 minutes to fall to half its starting brightness at 2.4 milliamperes per square centimetre; the authors say continuous long-term operation is currently limited to 10 milliamperes per square centimetre or less. The work therefore establishes a credible route to directly patterned multicolour organic emitters, not a manufacturing-ready panel. The next decisive evidence is independent fabrication on larger backplanes, with alignment yield, pixel uniformity and operating lifetime measured together. [1] [2]