Perovskite synthesis out in the open: Although methods have been developed that create the photoactive black perovskite phase of formamidinium lead iodide (α-FAPbI ₃ ), these routes are temperature and humidity sensitive and less compatible with large-scale solar cell production. Hui et al. report an alternative route in which vertically aligned lead iodide thin films are grown from the ionic liquid methylamine formate. Nanoscale channels in the films lower the barrier to permeation of formamidinium iodide and enable transformation to α-FAPbI ₃ , even at high humidity and room temperature. Solar cells made with these films have power conversion efficiencies as high as 24.1% that display high stability. Science , this issue p. 1359

Simultaneously achieving high efficiency and low efficiency roll-off remains a big challenge for OLEDs based on thermally activated delayed fluorescence (TADF) emitters. To address this issue, we elaborately designed and synthesized a series of new emitters with both TADF and aggregation-induced emission (AIE) properties by introducing 9,9-dimethyl-9,10-dihydroacridine (DMAC) or 10H-phenoxazine (PXZ) as donor units into a quinoxaline framework. By tuning the electron-donating capability of the donor as well as the amount of donor unit, the photophysical properties of the TADF-AIE emitters can be systematically regulated, with emissions ranging from green to red. We demonstrated efficient doped OLEDs with a maximum EQE of 22.4%, a maximum current efficiency (CE_max) of 80.3 cd A⁻¹ and a maximum power efficiency (PE_max) of 64.1 lm W⁻¹ for the green device, and an EQE_max of 14.1%, a CE_max of 36.1 cd A⁻¹ and a PE_max of 28.1 lm W⁻¹ for the orange device. Remarkably, these orange devices rendered small roll-offs of 1.4% and 21.3% respectively at a luminance of 100 and 1000 cd m⁻². Attributed to the unique TADF and AIE features, the non-doped devices perform outstandingly with an EQE_max of 12.0%, a CE_max of 41.2 cd A⁻¹ and a PE_max of 45.4 lm W⁻¹.

The exploitation of blue to orange emissive thermally activated delayed fluorescence (TADF) materials has been conducted comprehensively, while the equally important red TADF materials have been studied at a relatively slow pace. Three D–A–D structured fluorescent molecules, N⁴,N⁴,N⁷,N⁷-tetraphenylbenzo[c][1,2,5]thiadiazole-4,7-diamine (BTZ–DPA), 4,7-bis(9H-carbazol-9-yl)benzo[c][1,2,5]thiadiazole (BTZ–CZ) and 4,7-bis(9,9-dimethylacridin-10(9H)-yl) benzo[c][1,2,5]thiadiazole (BTZ–DMAC) were designed and synthesized by rationally employing 2,1,3-benzothiadiazole as an acceptor. The introduction of 2,1,3-benzothiadiazole not only presents an efficient input for the design of red TADF emitters, but also provides benefits for the resulting high-efficiency organic light-emitting diodes (OLEDs) which show a maximum external quantum efficiency of 8.8% at a luminance of 1.06 cd m⁻² with the emission peak at 636 nm.

A new orange-red thermally activated delayed fluorescence (TADF) emitter is designed and synthesized by incorporating a fluorine-substituted quinoxaline as an electron-acceptor and a phenoxazine as an electron-donor. The rational molecular design enables small singlet–triplet energy splitting (ΔE_ST) and high fluorescence radiative rate (k^S _r) for long-wavelength TADF emitters. The organic light emitting diodes (OLEDs) employing the new TADF emitter achieve maximum external quantum efficiencies (EQEs) of 13.9% and 9.0% for the vacuum- and solution-processed OLEDs, respectively.