Dual-mode photomultiplication organic photodetectors

Organic photodetectors (OPDs) are a promising alternative optical detecting technology to conventional wafer-based inorganic counterparts, because the optical and electric properties of the organic semiconductor materials can be tailored accordingly. They offer additional advantages such as having a solution-processable fabrication process, which also leads to significant cost benefits, thereby creating next-generation solution- processable, flexible and low-cost photodetectors. In general, the spectral responses of the photodetectors are determined by the absorption of the active materials and optical profile in the devices. Single-mode OPDs optimized for photodetection at the specific spectral ranges have been reported. Realizing dual-mode OPDs with high detectivity in two bands are very attractive for different applications. However, the reports on spectral tunable OPDs are rather rare. It is a great challenge to achieve a high performance OPD with dual-mode photo-responses in two distinct bands.

In this application, we propose to develop a novel dual-mode photomultiplication OPD with a unique tunable photodetection capability, particularly over the near-infrared (NIR) and visible light wavelength ranges, that can be operated by adjusting the polarity of the biases. A dual-mode OPD comprises a tri-layer visible light absorber/optical spacer/NIR absorber configuration. In the presence of NIR light, photocurrent can be produced in the NIR absorbing layer, due to the trap-assisted charge injection at the NIR absorber/cathode interface under a reverse bias. In the presence of the visible light, photocurrent can be produced in the visible light absorbing layer, enabled by the trap- assisted charge injection at the anode/visible light absorber interface under a forward bias. A bias-switchable spectral response dual-mode photomultiplication OPD offers an attractive option for a plethora of applications in environmental pollution, bio, medical, agricultural, automotive and security monitoring, detection and imaging in two distinct bands.