Photomultiplication Behavior of Chlorophyll-Based Photodetector under Biased Voltage.

In this study, we fabricated a photodetector (PD) with two types of chlorophyll derivatives, namely, zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (ZnChl) and methyl 13 1 -deoxo-13 1 -dicyanomethylene-pyropheophorbide-a (H 2 Chl'), via a two-step drop-coating process. In the absorption range of ZnChl/H 2 Chl' films, the maximum external quantum efficiency of ZnChl/H 2 Chl'-based devices reached 1363% at -8 V and 1345% at 2.5 V, exhibiting the photomultiplication (PM) phenomenon. The PM phenomenon of ZnChl/H 2 Chl'-based devices is attributed to hole tunneling injection from the external circuit assisted by electron accumulation in the ZnChl and H 2 Chl' under light illumination. Through the investigation of the responsivity ( R ) of ZnChl/H 2 Chl'-based devices, it has been found that achieving a high R is easier under forward bias compared with reverse bias (7706 mA/W at -8 V and 7629 mA/W at 2.5 V). The organic PDs based on ZnChl/H 2 Chl' exhibit PM behavior, offering a promising approach to improve the device's responsivity.