Highly Selective Ultrafast Circularly Polarized Photodiodes Based on π-Conjugated Polymers

Chiral π-conjugated molecular systems that are intrinsically sensitive to the handedness of circularly polarized (CP) light potentially allow for miniaturized, low-cost CP detection devices. Such devices promise to transform several technologies, including biosensing, quantum optics and communication of data encrypted by exploiting the spin angular momentum of light. Here we realize a simple, bilayer organic photodiode (CP OPD) comprising an achiral π-conjugated polymer–chiral additive blend as the electron donor layer and an achiral C₆₀ electron acceptor layer. These devices exhibit considerable photocurrent dissymmetry g_ph, with absolute values as high as 0.85 and dark currents as low as 10 pA. Impressively, they showcase a linear dynamic range of 80 dB, and rise and fall times of 50 and 270 ns respectively, which significantly outperforms all previously reported CP selective photodetectors. Mechanistically, we show that the g_ph is sensitive to the thickness of both the chiral donor and achiral acceptor layers and that a trade-off exists between the external quantum efficiency (EQE) and g_ph. The fast-switching speeds of these devices, coupled with their large dynamic range and highly selective response to CP light, opens up the possibility of their direct application in CP sensing and optical communication.