Photostability Improvement of Organic Photodiodes with ZnO Electron Transport Layer

The stable performance of organic photodiodes (OPDs) is crucial for realizing reliable photosensing and their facile integration into larger systems. However, OPDs with the commonly used ZnO electron transport layer (ETL) suffer from photoinstability, where the dark current increases by several orders of magnitude after light irradiation, thereby affecting the stability of their photodetection. Herein, the increase in the dark current after light irradiation in OPDs with ZnO ETL is suppressed to approximately twice its initial value. This suppression is achieved by improving the quality of the ZnO ETL by increasing the annealing temperature from the widely adopted 180–350 °C. In addition, irradiation with wavelengths longer than 380 nm exhibits a substantially smaller increase in the dark current after light irradiation, by a maximum of 17.6% of those with the sub‐370 nm wavelengths. Furthermore, using X‐ray photoelectron spectroscopy, a decrease in the spectral intensity related to defects in ZnO ETLs annealed at higher temperatures is observed, indicating their role in photoinstability. These findings highlight the importance of defect‐free ETL formation to realize photostable OPDs.