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 10¹³ 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.