In traditional optoelectronic approaches, control over spin, charge, and light requires the use of both electrical and magnetic fields. In a spin-polarized light-emitting diode (spin-LED), charges are injected, and circularly polarized light is emitted from spin-polarized carrier pairs. Typically, the injection of carriers occurs with the application of an electric field, whereas spin polarization can be achieved using an applied magnetic field or polarized ferromagnetic contacts. We used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrate a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts. The CISS layer consists of oriented, self-assembled small chiral molecules within a layered organic-inorganic metal-halide hybrid semiconductor framework. The spin-LED achieves ±2.6% circularly polarized electroluminescence at room temperature.

Incorporating chiral organic molecules into organic/inorganic hybrid 2D metal-halide perovskites results in a novel family of chiral hybrid semiconductors with unique spin-dependent properties. The embedded chiral organic moieties induce a chiroptical response from the inorganic metal–halide sublattice. However, the structural interplay between the chiral organic molecules and the inorganic sublattice, as well as their synergic effect on the resulting electronic band structure need to be explored in a broader material scope. Here we present three new layered tin iodide perovskites templated by chiral (R/S-)­methylbenzylammonium (R/S-MBA), i.e., (R-/S-MBA)2SnI4, and their racemic phase (rac-MBA)2SnI4. These MBA2SnI4 compounds exhibit the largest level of octahedral bond distortion compared to any other reported layered tin iodide perovskite. The incorporation of chiral MBA cations leads to circularly polarized absorption from the inorganic Sn–I sublattice, displaying chiroptical activity in the 300–500 nm wavelength range. The bandgap and chiroptical activity are modulated by alloying Sn with Pb, in the series of (MBA)2Pb1–x Sn x I4. Finally, we show that vertical charge transport through oriented (R-/S-MBA)2SnI4 thin films is highly spin-dependent, arising from a chiral-induced spin selectivity (CISS) effect. We demonstrate a spin-polarization in the current–voltage characteristics as high as 94%. Our work shows the tremendous potential of these chiral hybrid semiconductors for controlling both spin and charge degrees of freedom.

This work shows a bimolecular additive engineering approach to prepare highly efficient wide-band-gap perovskite solar cells. The coupling of PEA + and SCN À provides a synergistic effect that overcomes growth challenges with either additive individually and improves perovskite quality with enhanced crystallinity, reduced defect density, and improved carrier mobility and lifetime. When coupling a semitransparent wide-band-gap perovskite top cell with a low-band-gap CIGS bottom cell, we achieve a 25.9%-efficient polycrystalline perovskite/CIGS 4-terminal thinfilm tandem solar cell.

Colloidal metal halide perovskite nanocrystals (NCs) with chiral ligands are outstanding candidates as a circularly polarized luminescence (CPL) light source due to many advantages such as high photoluminescence quantum efficiency, large spin–orbit coupling, and extensive tunability via composition and choice of organic ligands. However, achieving pronounced and controllable polarized light emission remains challenging. Here, we develop strategies to achieve high CPL responses from colloidal formamidinium lead bromide (FAPbBr3) NCs at room temperature using chiral surface ligands. First, we show that replacing a portion of typical ligands (oleylamine) with short chiral ligands ((R)-2-octylamine) during FAPbBr3 NC synthesis results in small and monodisperse NCs that yield high CPL with average luminescence dissymmetry g-factor, g lum = 6.8 × 10–2. To the best of our knowledge, this is the highest among reported perovskite materials at room temperature to date and represents around 10-fold improvement over the previously reported colloidal CsPbCl x Br y I3‑x‑y NCs. In order to incorporate NCs into any optoelectronic or spintronic application, the NCs necessitate purification, which removes a substantial amount of the chiral ligands and extinguishes the CPL signals. To circumvent this issue, we also developed a postsynthetic ligand treatment using a different chiral ligand, (R-/S-)­methylbenzylammonium bromide, which also induces a CPL with an average g lum = ±1.18 × 10–2. This postsynthetic method is also amenable for long-range charge transport since methylbenzylammonium is quite compact in relation to other surface ligands. Our demonstrations of high CPL and g lum from both as-synthesized and purified perovskite NCs at room temperature suggest a route to demonstrate colloidal NC-based spintronics.

1411wileyonlinelibrary.com current-voltage ( I-V ) characteristics in planar perovskite PV structures, where the reverse scanning (from open circuit voltage ( V oc ) to short circuit current( J sc )) current is superior to the forward scanning (from J sc to V oc ) current. [6][7][8][9][10] Three mechanisms have been proposed [ 6 ] to explain the hysteresis behavior of perovskite PV cells: charge trapping at the interface between perovskite and its neighboring charge transport layers, ferroelectric response of perovskites, and migration of interstitial or vacancy defects in perovskites. In earlier studies, ineffi cient electron extraction (i.e., electron trapping) at the perovskite/compact TiO 2 (c-TiO 2 ) interface [ 11 ] was considered as the origin of the I-V hysteresis. It was shown that by replacing c-TiO 2 with mesoporous TiO 2 [ 6,12 ] or by modifying the c-TiO 2 surface with a C 60 self-assemble monolayer, [ 13 ] the hysteresis can be reduced. On the other hand, it was noted that in the hysteretic devices the response time of photocurrent upon voltage change is in the range of seconds or longer, while trapping/detrapping of charges should happen at much faster timescales. [ 9 ] Ferroelectric polarization may occur in the perovskite devices, but this mechanism alone cannot explain the variation of hysteresis upon interface modifi cation [ 13 ] and the absence of hysteresis in some planar PV structures, such as indium tin oxide (ITO) /poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/ perovskite/phenyl-C61-butyric acid methyl ester (PCBM)/ C 60 /2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/Al. [ 14 ] Recently, migration of ionic defects (e.g., Ii i or V i MA ) has been associated with the hysteresis behavior. [ 9,[15][16][17][18][19][20][21][22][23] Huang and coworkers demonstrated a giant switchable photovoltaic effect in both ITO/PEDOT:PSS/MAPbI 3 /gold (Au) [ 15 ] and lateral Au/ MAPbI 3 /Au [ 17 ] structures and explained the phenomenon by migration of methylammonium ions (MA + ) based on photothermal induced resonance measurement results. [ 17 ] Yang et al. investigated specifi cally the ionic conductivity of lead iodidebased perovskites by employing electrochemical cells, [ 18 ] and they found that the ion conduction is largely contributed by iodide ions (I − ). Eames et al. estimated the active energy of I − migration in MAPbI 3 to be 0.6 eV through chronophotoamperometry measurement of a fl ourine-doped tin oxide (FTO)/cTiO 2 /MAPbI 3 /spiro-OMeTAD/Au structure; [ 19 ]