Organic narrowband near-infrared photodetectors based on intermolecular charge-transfer absorption

TLDR

Blending organic electron donors and acceptors creates intermolecular charge‑transfer states that introduce additional optical transitions below their optical gaps, which are crucial in organic photovoltaic devices but often remain undetected due to their weak nature. The study aims to enhance the external quantum efficiency of charge‑transfer absorption in organic photodetectors using an optical microcavity. An optical microcavity is employed to boost the external quantum efficiency in the charge‑transfer absorption region by over 40 times, achieving values above 20 %. The device achieves narrowband detection with spectral widths down to 36 nm and resonance wavelengths from 810 to 1,550 nm, far below the donor and acceptor optical gaps, and its broad tunability via simple cavity thickness variation makes it a flexible, potentially transparent, low‑cost spectroscopic near‑infrared photodetector.

Abstract

Abstract Blending organic electron donors and acceptors yields intermolecular charge-transfer states with additional optical transitions below their optical gaps. In organic photovoltaic devices, such states play a crucial role and limit the operating voltage. Due to its extremely weak nature, direct intermolecular charge-transfer absorption often remains undetected and unused for photocurrent generation. Here, we use an optical microcavity to increase the typically negligible external quantum efficiency in the spectral region of charge-transfer absorption by more than 40 times, yielding values over 20%. We demonstrate narrowband detection with spectral widths down to 36 nm and resonance wavelengths between 810 and 1,550 nm, far below the optical gap of both donor and acceptor. The broad spectral tunability via a simple variation of the cavity thickness makes this innovative, flexible and potentially visibly transparent device principle highly suitable for integrated low-cost spectroscopic near-infrared photodetection.