Spin injection sans magnetism: Light-emitting diodes (LEDs) that emit circularly polarized light (spin-LEDs) have potential applications in in three-dimensional displays, bioencoding, and tomography. The requisite spin polarization of the charge carriers is usually achieved with ferromagnetic contacts and applied magnetic fields, but Kim et al. report on a room-temperature spin-LED that relies instead on a chiral-induced spin selectivity organic layer. This layer selectively injected spin-polarized holes into metal halide perovskite nanocrystals, where they radiatively recombined with unpolarized electrons with an efficiency of 2.6%. Science , this issue p. 1129

Chiral molecules in Pb-halide 2D-layered films achieve up to 86% spin-polarized transport, enabling novel spintronic applications.

In thermally activated delayed-fluorescence (TADF) materials, the fluorescence efficiency is enhanced through reverse intersystem crossing (RISC) from triplet to singlet excitons. The performance of organic light-emitting devices (OLEDs) based on TADF materials highly depends on the thermal conversion efficiency of the lowest triplet exciton $T_1$ into the lowest singlet exciton $S_1$, which relates to the energy difference $\mathrm{\Delta }{E}_{S_1-T_1}$. Here we investigate the RISC process in two TADF compounds with vastly different $\mathrm{\Delta }{E}_{S_1-T_1}$ using magneto-optical spectroscopies that include magnetophotoinduced absorption (MPA) in films and magnetoelectroluminescence (MEL) in OLEDs. The photoinduced absorption spectrum of the fast RISC material clearly shows that both singlet and triplet excitons coexist under steady-state conditions. Since the MPA response of the singlet and triplet excitons are similar and have the same polarity, we conclude that the magnetic field does not influence the RISC process in the studied compounds. We also find that the MEL response in OLEDs based on these compounds originates from the injected polaron pair species before they decay into $S_1$ and $T_1$ excitonic states in the emissive TADF layer.