Light Detection in Open‐Circuit Voltage Mode of Organic Photodetectors

Organic photodetectors (OPDs) are promising candidates for next‐generation light sensors as they combine unique material properties with high‐level performance in converting photons into electrical signals. However, low‐level light detection with OPD is often limited by device dark current. Here, the open‐circuit voltage ( V oc ) regime of OPDs is shown to be efficient for detecting low light signals (<100 µW cm −2 ). It is established that the light‐dependence of V oc exhibits two distinct regimes as function of irradiance: linear and logarithmic. Whereas the observed logarithmic regime is well understood in organic photovoltaic cells (OPVs), it is shown experimentally and theoretically that the linear regime is due to the non‐infinite shunt resistance of the OPD device. Overall, OPDs composed of rubrene and fullerene show photovoltage light sensitivity across nine orders of magnitude with a detection limit as low as 400 pW cm −2 . A photovoltage responsivity of 1.75 V m 2 W −1 demonstrates highly efficient performance without the necessity to supress high dark current. This approach opens up new possibilities for resolving low light signals and provides simplified design rules for OPDs.