Predicting Noise and Detectivity Limits in Organic Infrared Photodiodes with Low Disorder
Journal
npj Flexible Electronics
Date
2020.04.29
Abstract
In order to achieve high detectivity in infrared detectors, it is critical to reduce the device noise. Yet for non-crystalline semiconductors, an essential framework is missing to understand and predict the effects of inherent disorder on the dark current. This report presents experimental and modeling studies on the noise current in exemplar organic bulk heterojunction photodiodes, with ten donor-acceptor combinations spanning wavelength of 800―1600 nm. Significant noise reduction and higher detectivity are found in devices using non-fullerene acceptors (NFA) compared to those with fullerene derivatives. Low noise in NFA blends is due to a sharp drop off in the distribution of bandtail states, as revealed by variable-temperature density-of-states measurements. Taking disorder into consideration, a general physical model is developed to explain the dependence of thermal noise on the effective bandgap and the bandtail spread. The model provides theoretical targets for the maximum detectivity and detection wavelength in infrared photodiodes with disorder.