Researchers at the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem, led by Dr. Joanna Dehnel and Dr. Igal Levine, have introduced a contactless technique for probing how chiral 2D perovskites respond differently to circularly polarized light, without first building the material into a complete electronic device.
Chiral perovskites exist in two mirror-image forms, much like a left and right hand, and are of growing interest for spintronics and optoelectronics because their crystal structure can couple light polarization, electrical charge and electron spin without requiring an external magnetic field. Studying that coupling has traditionally meant fabricating a full device with metal contacts, a step that can introduce defects and other artifacts that obscure the material's intrinsic electronic response. To get around this, the team developed circularly polarized time-resolved surface photovoltage (CP-TRSPV), a technique that tracks how electrical charges separate inside the material under circularly polarized illumination, without a top electrical contact. The method can follow the resulting signal over an unusually wide time window, from nanoseconds to milliseconds.
Applying CP-TRSPV to R- and S-form chiral 2D perovskites, the researchers found that each mirror-image form preferentially responded to opposite circular polarizations: the R-form responded more strongly to right-circularly polarized light, and the S-form to left-circularly polarized light. A racemic sample, with no net mirror-image preference, showed no significant difference between the two, indicating that the effect originates from the crystal's chiral structure itself.
The size of the response was notable: the team measured a photovoltage anisotropy factor (gSPV) of about -0.7 in the R-form and 0.17 in the S-form, roughly 1,000 times larger than the anisotropy seen in simple light absorption by the two forms. The results are consistent with chiral-induced spin selectivity (CISS), in which the chiral crystal structure favors electrons of one spin orientation over the other, acting as a microscopic spin filter during charge separation. The researchers note that while the underlying spin-selective process is extremely fast, the resulting difference in separated charge populations persists far longer, from nanoseconds into the millisecond range, as those charges are trapped, released or recombine.
Beyond the specific result, the authors point to CP-TRSPV as a way to accelerate the search for useful chiral materials: rather than building a complete device for every new chiral composition, researchers could first use the contactless technique to screen how strongly a material responds, in a manner the authors say could extend to high-throughput studies. Potential applications for chiral perovskites include circularly polarized light detectors and other spin-based electronic devices.