Organic Photodiodes with Thermally Reliable Dark Current and Excellent Detectivity Enabled by Low Donor Concentration.

Reducing the dark current ( J d ) under reverse bias while maintaining a high external quantum efficiency (EQE) is essential for the practical application of organic photodiodes (OPDs). However, the high J d of OPDs is generally difficult to reduce because its origin in organic photodiodes is still not well understood and is strongly temperature dependent. To address the issues related to high J d in typical OPDs, we investigate fullerene-based OPDs with various donor concentrations. It is surprising that OPDs with a low donor concentration in the active layer can achieve a very low J d of 1.68 × 10 -7 mA cm -2 at a reverse bias of -2 V, which is almost temperature-independent owing to the low polymer content. More importantly, the fullerene-based OPDs with a low donor concentration of 5 wt % can still achieve an external quantum efficiency (EQE) as high as 40%, resulting in a promisingly high detectivity of above 10 13 Jones at 300-800 nm compared to the OPDs with a standard donor/acceptor ratio. The presented optimized OPD device can also be used for real-time heart rate detection, indicating its potential for practical photon-sensing applications.