Transition of Working Modes in Organic Photodetectors: Tuning the Electrode Work Function for Photodiode‐to‐Photoconductor Switching

Abstract

The two categories of organic photodetectors (OPDs) can be distinguished as the photodiode mode and the photoconductor mode. The role of the contact between the electrode and active layer in determining the specific type of photodetector is of utmost importance. In this study, the transition of working modes between the photodiode type and the photoconductor type in OPDs is demonstrated. Specifically, OPDs based on the indium tin oxide/Cs2CO3/P3HT: PC61BM/Al (or Au) structure are fabricated. In the corresponding characterization results, distinct working modes are showcased. For the device with the Au electrode, under reverse bias, the photo‐generated charges can efficiently transport to their respective electrodes and subsequently be collected. This behavior aligns with the photodiode type. Conversely, in the device with the Al electrode, the photo‐generated charges accumulate near the interface between the Cs2CO3 layer and the active layer. Subsequently, under reverse bias, tunneling charge injection occurs, resulting in the photoconductor type with an external quantum efficiency exceeding 100%. Both the photodiode and photoconductor devices exhibit a high signal‐to‐noise ratio ranging from 104 to 105 and fast response on the order of microseconds at −0.5 V. In these findings, the possibility of obtaining desirable working‐mode OPDs by manipulating the electrode work function is suggested.