Two-dimensional (2D) materials have been well developed for polarization-sensitive photodetection, while new 2D members used in shortwave region (>2.5 eV) still remain scarce. The family of 2D hybrid perovskite ferroelectrics, in which the coupling of spontaneous polarization (P s ) and light benefits dissociation of photoinduced carriers, has shown great potential in this portfolio. Here, we report a new 2D hybrid perovskite ferroelectric, [CH 3 (CH 2 ) 3 NH 3 ] 2 (CH 3 NH 3 )Pb 2 Br 7 (1), which exhibits a superior P s of 3.6 μC/cm 2 and a relatively wide bandgap (∼2.55 eV). The unique 2D perovskite motif results in an intrinsic anisotropy of optical absorption (the ratio α c /α a ≈ 1.9 at 405 nm), involving its polarizationsensitive activity. As expected, the strongest photoresponses were observed along the c-axis (i.e., parallel to P s ), along with a large dichroism ratio (I ph c /I ph a ≈ 2.0) and highly sensitive detectivity up to ∼10 9 Jones. Further, crystal-device of 1 shows a fast responding rate (∼20 μs) and excellent antifatigued merits. As pioneering work, 1 is the first polarization-sensitive ferroelectric in the new branch of 2D hybrid perovskites. Such intriguing behaviors make 1 a potential candidate for the shortwave polarized-light detection, which also sheds light on new functionalities for future optoelectronic application of hybrid perovskites.

The non-π-conjugated sulfate system has long been overlooked as potential deep-UV nonlinear optical (NLO) materials. Here we report two asymmetric anhydrous sulfates, namely, NH 4 NaLi 2 (SO 4 ) 2 (Ι) and (NH 4 ) 2 Na 3 Li 9 (SO 4 ) 7 (Π), which consist of non-πconjugated [SO 4 ] 2− anions. Their single crystals can be readily grown by a facile evaporation method from water solution. Both sulfates are transparent down to the deep-UV region. Interestingly, there is a large NLO gap between I and Π, with phase-matching NLO responses of 1.1 and 0.5 times that of the benchmark KH 2 PO 4 , respectively. The first-principles studies reveal that the non-π-conjugated [SO 4 ] 2− anions are the dominate NLOactive groups, and the large NLO gap between I and Π can be ascribed to the nonbonding O 2p orbitals of different orientations in the crystallographically independent S1O 4 groups. This work provides an innovative non-πconjugated source that is distinct from the traditional πconjugated ones for deep-UV NLO materials.

Large-size crystals of organic-inorganic hybrid perovskites (e.g., CH 3 NH 3 PbX 3 , X = Cl, Br, I) have gained wide attention since their spectacular progress on optoelectronic technologies. Although presenting brilliant semiconducting properties, a serious concern of the toxicity in these lead-based hybrids has become a stumbling block that limits their wide-scale applications. Exploring lead-free hybrid perovskite is thus highly urgent for high-performance optoelectronic devices. Here, a new lead-free perovskite hybrid (TMHD)BiBr 5 (TMHD = N,N,N,N-tetramethyl-1,6-hexanediammonium) is prepared from facile solution process. Emphatically, inch-size high-quality single crystals are successfully grown, the dimensions of which reach up to 32 × 24 × 12 mm 3 . Furthermore, the planar arrays of photodetectors based on bulk lead-free (TMHD)BiBr 5 single crystals are first fabricated, which shows sizeable on/off current ratios (≈10 3 ) and rapid response speed (τ rise = 8.9 ms and τ decay = 10.2 ms). The prominent device performance of (TMHD)BiBr 5 strongly underscores the lead-free hybrid perovskite single crystals as promising material candidates for optoelectronic applications.

Multiaxial molecular ferroelectrics, in which multiple-directional switching of spontaneous polarization creates diverse properties, have shown many intriguing advantages, making them indispensable complements to conventional inorganic oxides. Despite recent blooming advances, multiaxial molecular ferroelectric with bulk photovoltaic effects still remains a huge blank. Herein, we report a biaxial lead halide ferroelectric, EA 4 Pb 3 Br 10 (1, EA = ethylammonium), which adopts the unique trilayered perovskite motif with a high Curie temperature of ∼384 K. Particularly, for 1, the distinct symmetry breaking with 4/mmmFmm2 species leads to the emergence of four equivalent polarization directions in the ferroelectric phase. Based on its biaxial nature, the bulk photovoltaic effect of 1 can be facilely tuned between such multiple directions through electric poling. As far as we know, this is the first report on biaxial hybrid perovskite ferroelectric showing directionally tunable photovoltaic activity. This work provides an avenue to control the bulk physical properties of multiaxial molecular ferroelectrics, and highlights their potential for further applications in the field of smart devices.