Response Speed of Organic Photodiodes as a Function of Incident Optical Intensity

Different approaches have been introduced to raise the response speed of bulk heterojunction-based organic photodiodes (OPDs), with the best-performing devices now having speeds in the MHz range. In most organic photodiodes, the response speed is commonly assumed to be due to transit time of charge carriers. Upon investigating fluence-dependent photoresponse of different OPDs, it is found here that bimolecular recombination dictates the response speed at higher fluence levels. Herein, four different organic blend based photodiode systems and their response speed to a range of incident optical fluences are reported. A steep variation in response speed, depending upon the blend system is observed. Using experimental and theoretical studies, the intensity-dependent response speeds are attributed to differences in the suppressed recombination factor. A high factor enables faster response times in the regime of higher light intensity. This new approach to high-speed detections has implications for the design of high-speed organic photodetectors, especially in applications where the speed of the photodetector is most important irrespective of the intensity of the incident signal.