Bulk Photovoltaic Effect Along the Nonpolar Axis in Organic-Inorganic Hybrid Perovskites

Giant Bulk Photovoltaic Effect in a Chiral Polar Crystal based on Helical One-dimensional Lead Halide Perovskites

Chiral polar crystals composed of one-dimensional (1D) conducting materials exhibit unique physical phenomena. The present study focused on helical 1D-structured lead halide perovskite derivatives with chiral naphthylethylamine as organic cations, (R or S-NEA)[PbI3](R-NEA=R-(+)-1-(1-naphthyl)ethylamine, S-NEA=S-(-)-1-(1-naphthyl)ethylamine). A thermally controlled crystallization method has successfully yielded crystals with a polar chiral space group of C2. The crystals show significantly intense signals of circular dichroism (CD) originating from the asymmetrical electronic transition characteristic of helical 1D structure. In addition, generation of an anomalous zero-bias photocurrent (bulk photovoltaic effect (BPVE)) was observed with an open-circuit voltage up to 15 V, which is five times larger than the band gap. This study suggests that parallel arrangements of the helical semiconducting materials are the promising way to obtain chiral polar crystal exhibiting high performance BPVE.

Emerging Nonlinear Photocurrents in Lead Halide Perovskites for Spintronics

Lead halide perovskites (LHPs) containing organic parts are emerging optoelectronic materials with a wide range of applications thanks to their high optical absorption, carrier mobility, and easy preparation methods. They possess spin-dependent properties, such as strong spin-orbit coupling (SOC), and are promising for spintronics. The Rashba effect in LHPs can be manipulated by a magnetic field and a polarized light field. Considering the surfaces and interfaces of LHPs, light polarization-dependent optoelectronics of LHPs has attracted attention, especially in terms of spin-dependent photocurrents (SDPs). Currently, there are intense efforts being made in the identification and separation of SDPs and spin-to-charge interconversion in LHP. Here, we provide a comprehensive review of second-order nonlinear photocurrents in LHP in regard to spintronics. First, a detailed background on Rashba SOC and its related effects (including the inverse Rashba-Edelstein effect) is given. Subsequently, nonlinear photo-induced effects leading to SDPs are presented. Then, SDPs due to the photo-induced inverse spin Hall effect and the circular photogalvanic effect, together with photocurrent due to the photon drag effect, are compared. This is followed by the main focus of nonlinear photocurrents in LHPs containing organic parts, starting from fundamentals related to spin-dependent optoelectronics. Finally, we conclude with a brief summary and future prospects.

Tuning ferroelectric phase transition temperature by enantiomer fraction

Tuning phase transition temperature is one of the central issues in phase transition materials. Herein, we report a case study of using enantiomer fraction engineering as a promising strategy to tune the Curie temperature (TC) and related properties of ferroelectrics. A series of metal-halide perovskite ferroelectrics (S-3AMP)x(R-3AMP)1-xPbBr4 was synthesized where 3AMP is the 3-(aminomethyl)piperidine divalent cation and enantiomer fraction x varies between 0 and 1 (0 and 1 = enantiomers; 0.5 = racemate). With the change of the enantiomer fraction, the TC, second-harmonic generation intensity, degree of circular polarization of photoluminescence, and photoluminescence intensity of the materials have been tuned. Particularly, when x = 0.70 - 1, a continuously linear tuning of the TC is achieved, showing a tunable temperature range of about 73 K. This strategy provides an effective means and insights for regulating the phase transition temperature and chiroptical properties of functional materials.